Wall to wall sunshine!

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Sunday: All day sunshine! I have spent the entire day out in the observatory. A dark area and a spot are visible in H-alpha but nothing can be seen in white light in the 7". A triple, "chimney stack" prominence is also visible in H-alpha.

I am getting a dark doughnut of increased surface detail imposed on the sun's disk. Presumably an effect of the donor PST's etalon.

The sun is so low that the shadow of the house chimney has passed across the dome. At 14.30 CET the sun is only 8° in altitude according to Stellarium. I am still getting remarkably clear views with sharp edges to the disk at any power tried so far.

The T-E binoviewers provide excellent views of the sun. Allowing me to let my eyes wander effortlessly in the search for fine detail. I only have three pairs of eyepieces so far. 32, 26 and 20mm. Even with the 32mm EPs the 2.8x T-E GPC produces a huge image. It might be useful when the sun is high in the sky but not very practical at this time of year. As I finish scribbling this after lunch I can see the shadow of the house ridge rising up the dome.

Being able to spend hours in the dome during the day is very satisfying. It is warmer than at night and better sheltered than being outside. I can see what I am doing and can safely avoid the things which catch me unawares in the dark.

The next step is to move the computer "desk" shelf to the north side of the pier. It seemed most natural on the east side but I couldn't see the computer screen from the eyepiece.  The telescopes don't usually sweep across the north side of the pier. Which makes it much safer to carry out long slews. Perhaps I can come up with an edge hinged, shelf arrangement to allow viewing from any angle. If I have the shelf on the north side I shall be looking straight into the sun. Two, drop-down, hinged shelves?

I need to add more tube rings to the 6." These will help me support the weight of the binoviewer and a pair of low power eyepieces on the end of a stiff aluminium bar/tube. A simple plate, to act as a supporting bridge on the end, should be all that is required. A bolt or stud joining the plate to the tube will allow for some adjustment.The tube rings can be moved around the main tube to bring the support directly underneath regardless of the OTA's angle. Fortunately I have a couple of older tube rings as spares. I don't want anything bulky which would hinder etalon tuning or focusing.

Monday: The 6" tube rings proved to be the wrong size. So I bolted the offset counterweights for the 6" to the tube rings of the 7" instead. I had used cord to check if the weights helped and now they could be fixed properly. They used to clank unexpectedly as they dropped with changing OTA attitude. Which was always a shock when the sound was amplified by the 8" steel tube inside a silent dome!

Tomorrow a low passes east of us with winds forecast to gust to 50mph for at least 12 hours. I hope the obs doesn't blow over! It didn't and the wind was hardly noticeable as I pottered about improving details.

Click on any image for an enlargement.

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AWR Simple handset Pt2. Sunshine!

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Friday 28th Dec 2018 44F: An unexpected hour of sunshine in the late morning had me back up in my observatory. The Sun was blank in white light but had two prominences in H-alpha at my 10 o'clock. [Western limb.]

The [new] Simple Handset paddle was excellent for centering the sun at the eyepiece. I adjusted it to hang with enough cable drop to avoid pulling directly on the OTAs. I have finally adjusted the 6" to match the field of view of the 7." This will save constant adjustment between the two to check for matching features on the Sun.

I tried various filters to bring out any surface detail and then with the binoviewers viewed 'straight through.' [No 45 elbow or star diagonal.]

Now I need a pair of 20mm eyepieces for a larger image. The pair of 26mm Meade 4000 offer a slightly smaller image than I would like. Adding GPC elements boosts the power far too much. A second Meade 4000 in 20mm makes slightly more sense than a new budget pair.

The image on the laptop screen was far too large in the Celestron Neximage5 so I soon gave up on that.  It needs a proper spring clean to get rid of all the dust on the optics and "naked" camera sensor.

The AWR drives are working well on my big mounting now. I can just leave them to run for hours after Syncing on the sun in C-Du-C. No heat is detected on any of the components except the power supply warms a little after several hours. Slews and Gotos still need watching due to the large pier. The telescope could easily collide with the pier if I don't constantly monitor the clearance.

The dome slit is very easily advanced at intervals, via the crank, to keep the view clear for the telescopes. This is quickly becoming almost routine. Anticlockwise on the crank moves the dome anticlockwise.

Much heavier cloud has arrived from the northwest so I busied myself making minor improvements. The thermometer is now on the southern wall fixed to the SW 4x4 to avoid direct sunshine through the slit. The 'outdoor' sensor is located in deep shadow, year round, where the sun's heat cannot affect the readings. The idea is to compare the two readings to show the difference in temperature and whether that affects "dome seeing" or not. If warm air flows constantly out of the observing slit then it will spoil the view through the telescopes.

This is not the same thing as poor atmospheric "seeing" but is much more localized. My observatory is well ventilated and enjoys quite a chimney effect through the open doors down on the ground floor. That said, it is midwinter, so the sun has little heat to warm the dome so far. I need a solar screen to stop myself being blinded by the sun while looking through the telescopes.

I can't remember having seen more than a 2°F difference between inside the dome and outside, in the shadows under the veranda. The entire structure is thermally light so I am hoping for almost no solar gain. Buildings of blocks or bricks tend to soak up heat and let it out slowly over time. A wooden structure should not gain remotely as much heat and should dump it quite quickly using ventilation. I could have improved matters with white paint on the dome but wanted something much less visible from a distance.

Click on any image for an enlargement.

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The AWR Simple Handset.

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With the IH2 handset anchored by two cables to the computer area I needed a way to center the image before syncing a Goto slew. I had expressed some worries over the stiffness of very cold cables to Alan Buckman at AWR. However the serial cable attached to the Simple Handset seemed nicely slender and flexible.

I hope to run the cable along the 7" OTA and hang the neat little handset [paddle] near the focuser. If permanently attached and balanced it should not alter the behaviour of the mounting regardless of where the telescope is pointed. Images will follow after lunch.

 Here you can see the handset with a central red LED to make it easy to find in the dark. Three speeds are offered to allow fine, medium and coarse adjustment [slewing] of the telescope's pointing position on the sky.

I used thin black cord and Prusik loops to attach the cable neatly to the 7" OTA. These multi-wrapped loops allow the cable to be slid through when desired but lock the cable at all other times.

The telescope didn't even notice the addition with regard to balance. Having control at the eyepiece for centering an image was the requirement and now I have it. The telescope must not be moved manually or the system will lose track of its position. It was all too tempting to give the telescope a  nudge when the IH2 was several feet away, back at the computer.

The Simple Handset cable is 3m long and joins the AWR Microstep Drivebox via a serial plug.

The buttons on the handset are nicely spaced to allow simultaneous slewing of both axes with one hand. The buttons are nicely shaped and the spring weighted for a comfortable press without pain or fatigue.

The Simple Handset supplements the much bulkier Intelligent Handset 2 but does not replace it.

Click on any image for an enlargement.

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Boxing day: Dome rotation video.

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Despite being heavily overcast I thought I'd try and take some videos of the dome turning under crank power. The idea was to capture the dome in more even light. Of course the AS15 action camera's battery was flat. Now I'll miss the brightest part of the day. I eventually managed to capture a usable video but YT has made the quality almost unrecognizable in comparison with the original as I see it at home.

The 7" f/12 refractor was pointed at Polaris for scale. The wireless, camera controlling tablet sits on the back of the car near a builder's folding stepladder. A long telescopic windowcleaner's pole is strapped to the stepladder for stability with the action camera mounted on the pole's crossbar. I hit the red button on the tablet screen and then head for the observatory to capture the moment.

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WARNING: Google/YouTube is now falling over itself to auto-play the next completely unrelated video when an embedded video ends. So you could get YouTube porn or a YT rabid religious atrocity video showing on a blog aimed at a family audience.

They [Google/YouTube] have actually removed the previous control box to switch off auto-play of "related videos."

All the previous online advice on changing the URL no longer works either.

This is a DELIBERATE CHANGE in Google's policy for hosting videos because THEY MAKE SO MUCH UN-TAXED PROFIT GLOBALLY FROM EMBEDDED VIDEO ADVERTISING.

I was just monitoring my latest video using headphones and high volume to check for unwanted background sounds. When I was suddenly deafened by a jet fighter video auto-playing at ridiculous volume after my own embedded video with  QUIET RURAL background ended. How can GOOGLE/YOUTUBE possibly claim this racket is related to a quiet video on a rural, astronomical observatory?

There is now so much porn on YT that children are almost bound to be subject to unwanted abuse of their innocence and senses by this DELIBERATE change of policy by GOOGLE/YOUTUBE.

Click bait fraud via salacious, music video thumbnails is now commonplace on YouTube. So that one can only assume that Google/YT greatly value this DELIBERATE fraud provided it sells their advertising. Reporting such behaviour using the tools provided goes completely unnoticed by the advertising dictatorship.

Simultaneously VIMEO are FALSELY ADVERTISING their Basic hosting service online. ONLY AFTER they have captured your full name, email address and password on their initial sales web page will you discover that Basic no longer exists! Now they want £8 equivalent per month for their minimum Pro hosting service after a month's free trial. Beware of false advertising fraud disguising itself as the innocent tooth fairy!

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Christmas Day 2018.

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Christmas Day: A bout of sunshine after 11am but it soon clouded over again. I went over to let the light in but there was soon no sun to observe.

A merry Christmas to all my readers and particularly to those who have kindly offered advice during my building projects. Being banned from CN for mentioning "alternative" solar observation instruments meant that I could not properly thank my regular team of expert advisers.

Thank you for all the time and effort you all put into sharing your expertise.  Even if I didn't always follow your advice it was invaluable in giving me options and generating new ideas. It all added to my armoury of possibilities within my own, very limited capabilities.

Working entirely alone, as a septuagenarian, with occasional help from my wife, was bound to affect the final outcome. The result, as far as I am concerned, is still very satisfying both practically and aesthetically. Moreover it has raised me above many of the local obstructions for the very first time.

My observatory and no doubt others, are all the better for your contributions to the sum of human knowledge. You made it happen by setting a very high bar for me to aim for. One I readily accepted to push myself beyond all previous, personal standards or expectations.

My observatory isn't perfect, but it provides the basis for ongoing improvements as time, funds and inspiration allow. Above all, it provides vital shelter for my equipment. While allowing almost instant access, adequate security and rapid shut down. Advantages by which all observatories should be judged. After decades of observing on open lawns I highly recommend an observatory to those who can manage to build or obtain one. 

A sincere thank you to everybody who offered me guidance. You know who you are.

Click on any image for an enlargement.

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Christmas Eve fleeting solar glimpses.

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Monday: 33-38F, fast moving cloud clearing very slowly from the west/northwest.

The sun is sneaking along the ridge of the house 12° maximum altitude and falling to 8° with only the briefest glimpses of sunshine in the 180/12 [7"] at 68x with Baader full aperture solar foil filter. No sign of any surface activity so far.

H-alpha in the 6" f/8 [120mm f/10 equivalent] is dim at 38x and 46x and showing no sign of any prominences. The eyepieces keep fogging up so I am rotating them through my jacket pockets. The dome drive crank is proving excellent at moving the dome on at intervals to follow the sun with the observation slit. Well worth the effort. I need to pack out the 6" rings to match the 7". Their optical axes do not quite coincide by about half a field of view.

The 8x50 finder is handy for initial location of the sun by its own shadow and the projected image of the sun. I just need to remember not to look though it. As it is quite inaccessible when the sun is so low there is a very low risk at present.

I must admit to really enjoying solar observation now I have the correct tools for it. I shall also enjoy imaging once the sun gets high enough to make it worthwhile. Shame I chose to start taking it seriously just as the sun enters its minimum activity.

There is still months of work to finish off the observatory and mounting properly. So I shall have plenty to do when it is cloudy.

Click on any image for an enlargement.

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Dome drive crank 6: Eventual success.

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Wednesday: Now the wheels have fallen off again. Not quite literally, but close. The Connect BB is a simple axle with two bearings and a loose sleeve trapped between them. The bearings are unsupported externally unless they are housed in a close fitting tube and trapped between the threaded end cups. I was clamping at only one end cup which is a bit unfair. 

As I was cranking the dome around the outer, unsupported, bearing became loose. There followed a search for a suitable length of tubing to house the outer bearings.Which task, as donor, eventually fell to an old Nilfisk vacuum cleaner tube. I used enough length to hide inside the 2x4 as well as to contain and support the bearing. 

The dome returned to flying around effortlessly thanks to my cranking. I had added a 5kg weight to the far end of the, now much shorter, 2x4. This proved adequate except when the weight dipped and rested on the octagon's top ring. So I need a more compact weight than the disk I used on edge. It couldn't lie flat because there just wasn't room.

Then I remembered an old, iron, 5kg, conical scale weight and fixed that to the 2x4. Much better looking and it maximized the moment.[Mass x distance from pivot.]

It kept raining on and off so I had to keep closing the shutter doors. Which meant I needed artificial light without wrapping the cable around every obstacle in its path as I cranked the dome around.

I still have a couple of problems to solve. The pivot in the 2x4 is too lose and getting worse. I can use the original needle bearing from the friction roller to fix this.

The other problem is the BB bearing housing twisting in the 2x4. Just my luck to buy a BB which is not one sealed unit. The support tube I added is already loose in the 2x4. I wrapped it tightly in electrical tape but that didn't hold for long. I shall just have to add a short length of 2x4 onto the face of the 2x4 lever to better support the tube.

Thursday: Bought a Shimano BB @ 127.5mm with a hopefully better bearing retention. It doesn't rotate with hand pressure so there may be hope. I shall retain the bearing in the stub of steel tube from the start but clamp it firmly this time.

Friday.: A wet day so I should get on with modifying the lever. Instead of which I spent the day shopping.

Saturday: Another wet day but I fitted the needle roller bearing and its sleeve to a 26mm hole bored in the 2x4. This provided the rigid pivot base I needed to keep the friction roller aligned with a tangent on the base ring. I rebuilt the crank/roller bearing using the Shimano BB. Now the drive roller worked as expected without slipping or steering the dome sideways.

I made a new friction wheel bush, from another left side crank. This time with a large flange to stop the bush from sliding  inside the wheel bore as had the original. I even made a slight taper to ensure the wheel locked itself into the bush.

Cranking is almost effortless and can move the dome from a crawl up to high speed in full circles when required. The 6.5:1 lever ratio provides over 30kg of force at the friction roller interface. The cut down plastic, bicycle pedal provides an excellent and comfortable grip as a crank handle. Being plastic it avoids having to handle a cold, metal handle.

Click on any image for an enlargement. 

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Dome drive crank 5.

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Tuesday: The friction wheel drive looks very promising despite the doubts expressed by experienced forum members. Those who failed probably did not have my wide and flat plywood, dome base ring. Nor did they, probably, use enough pressure or the same 4" wheel size and type of tyre. The tyre is so grippy on the plywood underside of the base ring, that it pulls to the side if not absolutely tangential.

The first image shows the BB locked into the 2x4 by an alloy plate. A hidden lock-ring sits behind the plate embedded in the 2x4. The bolts holding the plate ensure a lack of movement.

 The second image shows the necessary offset to achieve tangential drive.

I don't see that I have much choice than to stick to a manual drive given my very limited abilities with electronics and modern software. The crank requires very little effort to turn the dome. So it will hopefully extend my ability to continue observing into ripe old age.

The third image shows the 2x4 lever, the crank and the friction roller in place. I still need to trim back the steering wheel bracket so that I can move the BB nearer to the apex of the octagon angle. At the moment the crank strikes the extended stainless steel [shelf] bracket if it gets too close.

It is an interesting challenge to achieve the correct geometry using familiar items from some of my other pastimes. Total cost should be under £30 equivalent. All constructive time consumed is my own. Just keeping up the insurance premiums on my own, active longevity.

The fourth image shows a clamped roller pressing with a through bolt for the 2x4 pivot. The extra extension of the BB axle had allowed me to bridge the 2x4. This worked fine for a full 360° until the roller moved inwards on the BB axle. There was nothing to restrain it from moving inwards. Only outwards. Easily fixed tomorrow.

I could have chosen a bulkier crank and left a flange but couldn't get the pedal off after years of attachment. The crank came with a recycled bike from a flea market. So the thread was probably never greased before fitting.

I knew the roller needed more work but I didn't want to waste time on that. Just in case the friction roller idea didn't work at all. The 2x4 set-up still looks horribly crude to my eyes but I'll persevere until I get it working faultlessly. Then  I can make it look a bit prettier. A length of square section, scrap aluminium tube? We shall see.

Motor drives, with slaving to the telescope movements, is much favoured by those with the necessary knowledge and skill. Which I mostly lack in that direction. What with affordable, AI domestic robots just around the corner, I think I'll wait for mine to crank the dome around. At whatever rate seems most suitable at the time. I just hope it can manage the stepladder! Or I'll have to make it a chain drive down to the ground floor. Which rather defeats the purpose.

Click on any image for an enlargement.

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Dome drive crank 4.

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Monday: 32F/ 0C all day. My new and longer bottom bracket [131mm] arrived today despite being ordered mid-afternoon on Sunday. It provided much more clearance for the crank from the octagon woodwork. My first deliberately skewed hole with a hole saw meant that the crank hit the 2x4. Whoops!

So I drilled a perpendicular hole instead. This proved that the friction wheel provided the perfect gear ratio to drive the dome. However, now I could not keep the 2x4 steady enough for a long slew. I'm still 35mm short of the correct hole-saw so will have to go shopping to make any further progress.

14 miles and one 35mm hole-saw later and I began making better progress. I chamfered the back of the 2x4 to let in the BB for even more crank clearance. An aluminium plate, bolted onto the chamfer, will lock the BB securely in place.

I now need to make a firm pivot to support the 2x4 close to the friction roller from the far side alone. It cannot overlap the front of the 2x4 [as previously planned] because the crank would strike it. Surprisingly little pressure on the 2x4 lever is required to ensure sufficient grip on the roller to drive the dome steadily.

It's not a lot of fun working at 32F in semi darkness with a solidly overcast, leaden sky and short hours of what might, half jokingly, be called "daylight." Back and forth between the dome "upstairs" and the workshop at ground level. Up and down the cold, metal stepladder.
 

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Dome drive crank 3.

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Saturday:

I'm now looking at a simple lever to force the crank driven friction roller upwards against the underside of the dome base ring. On the far end of the lever will be a screwed rod [stud or all-thread.]

The leverage will amplify the upward pressure on the roller. Until the point where adhesion is guaranteed. The drawing shows the basic idea. The hand crank is not to scale.

It will need a bearing in the back of the friction roller and adequate support from both sides if heavy pressure is required. The BB axle adapter I made yesterday is just for ensuring the drive from the crank to the roller.

I shall make the lever as long as possible to maximize the leverage. Ideally it won't need a screwed rod for adjustment. A simple weight at the far end and the lopsided 'seesaw' should easily absorb variation in base ring level. Thereby maintaining enough friction between the roller and base ring for a nice, even drive without slippage.

The next step is to build a rough model from scrap timber to test whether the friction roller really will work reliably. I will also get a good idea of the force required on the crank handle to move the dome easily. Then I can decide if I need a further gear reduction. Or can safely gear up for faster slews.

The image [Left] shows the general idea as a mock-up. The batten shown is not large enough to enclose the BB cartridge. Which will require a hole with a horizontal slit and vertical clamping bolts to hold the BB firmly. Something like 2" x4" timber, set on edge should do for a first trial.

Note I have trimmed the plastic, pedal plates away to make a comfortably round, crank handle. I have "painted" over the supporting blocks in the image to make the mock-up look more like the finished design. As shown, a ratio of 12:1 or even 15:1 on the lever is easily achieved.

The friction roller and its supporting BB bearing are skewed at an angle to the batten to achieve a tangent to the roller's track on the base ring. This will not affect the lever system in any meaningful way. The pressed steel roller bracket, from which the friction roller was removed, will provide a firm pivot for the eventual lever and allow it to sit close to the friction roller. 

The image [Right] shows a plan view of the lever, roller and BB. The offset angle [12-15 degrees] is easily seen to ensure the roller lies on a tangent to the base ring.

It will be important to resist any twisting in the final mechanism. So that the crank turns in a true circle and does not hit the woodwork. There isn't much room to swing a crank due to the angles of the broad, timber, top ring of the octagon. The long lever can be sandwiched between vertical restraints to reduce twisting to a minimum.

Hopefully the closeness of the lever pivot to the roller and the restraint from the base ring on the roller, will minimize unevenness in crank resistance during manual dome "winding." The rise and fall of the far end of the lever will have to be checked during a full dome rotation to avoid collisions. The 2x4 lever can easily be trimmed to a taper, if necessary, to provide more clearance.

The last image shows a length of 2x4 propped up in roughly the correct position. It will have to move a couple of inches towards the white roller to surround the sealed, bottom bracket cartridge. The 2x4 will have to be drilled 31mm diameter at 12-15° to the face. Probably using a hole saw but I don't have one of that size. A long, vertical bolt will clamp the body of the BB cartridge into the hole through the 2x4.

I also need a left hand thread, fixed wheel sprocket, locking ring. A metal plate fixed onto the face of the 2x4 will be clamped to the near side of the BB cartridge, with the locking ring, to further secure it under load. I'm wondering if I can get a much longer axle in a sealed BB cartridge to give me more clearance for the crank. Sealed BBs are readily available in lengths up to 131mm and are quite inexpensive. Duly ordered a cheap 131mm to replace my present 118mm. This will give me another 12mm [1/2"] clearance. I am now looking at adding metal plates for both sides of the timber lever to make use of the threaded sections of the BB.

Click on any image for an enlargement.

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Dome drive crank 2.

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After flirting with the idea of a [geared] electric motor drive I have opted for a safer and simpler hand operated crank. 

I am going to use a sealed bicycle bottom bracket bearing and crank. I have several sealed bearing bottom bracket [BB] "cartridges" with square axles. The bearing housing could be housed in a simple tube. Or clamped into reinforced 3/4" plywood uprights or box sections. The donor parts are shown in the image [Right.]

I need stiffness in the bearing supports to avoid too much flexure while cranking. This requirement may be at odds with a hinged and sprung base to ensure the friction roller remains in continuous contact with the underside of the dome's base ring.

The crank, BB bearing and pedal axle are the easy bit. Fixing the 4" friction roller to the other end of the axle is more difficult.

Removing the needle  bearing components left me with a 27mm bore in the cast iron roller. A more generous size in which to fit the turned down, crank stub.

This is what I did with another spare left side crank. [Image right of the cut down, crank/wheel adapter in the lathe.] Not much left of the poor old crank!

So far so good. Now I need to support the friction roller in the correct place while avoiding the crank striking the framework. It also has to be spring loaded to ensure continuous contact of the roller. The cheap, plastic pedal will be pared down to its axle casing to provide a smooth handle.

The image left shows the crank and wheel posed in the correct place. The wooden block is just a temporary support. If I removed the white wheel the friction roller would become the support and rotation device. No spring required but much greater demand on the support and roller to take its share of the dome's weight. Probably not a good idea.

Click on any image for an enlargement.

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Dome drive crank?

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Wednesday: I have plans to add a crank to a supporting wheel to drive the dome manually and relatively effortlessly. Until now I have relied on dragging the dome around by sheer strength while pulling on the plywood ribs. The dome's turning friction is rather variable due to the uneven base ring. This is aggravating my "tennis elbow."

I have already discovered that I can turn one of the white supporting wheels/rollers with my bare hands. This achieves dome rotation but it needs great care to avoid my fingers becoming trapped.

It is hardly a sensible way to turn the dome through a large angle but the effort needed seems quite low. This is because the gearing is in favour of the much smaller wheel riding against a much larger one. In this case the larger "gear" is the dome base ring. Which is roughly 3m or 10' in diameter.

The white wheels are 160mm or just over 6" = ~0.5' : 10' [dome Ø] = roughly 1:20 with a similar increase in torque. Ideal for hand cranking but it would need a very low speed, gearbox motor to drive it with electricity.

The white dome support rollers typically run on needle roller bearings for low friction and high load capacity. Which wouldn't provide any drive [at all] via a driven axle.

So I think I will modify one of my smaller 4" industrial wheels and brackets. These have rubbery [polyurethane?] treads which should provide far more grip for driving and considerably lower gearing. 4" : 120" = 1:30.

The drive wheel [base] ought to be sprung to ensure continuous contact with the rather non-flat, dome base ring.

I have propped one of these 4" industrial wheels up on a block of 2"x 4" to show the relative diameters. If I remove the sealed needle roller bearings the bore is a good size for fitting a sturdy, fixed, drive axle. I'll need to think about adding bearings to the uprights of the sprung support structure. This will need to avoid flexure while I am cranking.

My real worry is having a crank projecting into the dome area precisely at head height. I suppose I could rely on the drive crank being left in an upwards position of its circular travel. Then it might miss my head as I move around inside the dome. Cranking at head height might become irritating after too much practice. Though I have no plans to drive the dome continuously.

Where to site the wheel and crank is quite an important matter. The telescope's eyepiece end sweeps low, mostly from east to west, via north. So the drive crank wants to be on the southern side of the building. Where the telescope dewshield is usually pointing well above horizontal.

The southerly half of the dome is the least cluttered area so most suitable. It would make sense to have the crank on an inside corner of the octagon where it would protrude the least. South east makes most sense since it is nearest the computer shelf. South west would be near the top of the stepladder. So would offers a risk of a collision as I stepped onto the observatory floor from the top of the ladder.

It might prove necessary to add some gearing to lower the drive effort even more. This would also allow a lower crank situation via [perhaps] bicycle sprockets and chain. Or V-belt and pulleys. Even if the direct gear ratio is perfect, a chain or belt would allow the crank to be placed where it is most comfortable to use. Though there is always the matter of the crank whizzing round if the dome is rotated directly by hand. I shall just have to resist the temptation to do so.

Click on any image for an enlargement.

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Cloud watching.

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Wednesday: Spent a few seconds looking at the sun in several hours of waiting for clouds to clear. It has been getting worse instead of better. The sun is only about 10 degrees above the horizon so there is a very long path for cloud to intervene.

I had the Neximage5 in the 7" and then in the H-a 6" but any image on the laptop screen was only measurable in the microseconds. The Neximage5 is very unreliable and the connection keeps getting dropped. I think the mini-USB socket is poor, loose or badly soldered. It has been like this from brand new. The slightest change in the cable tension causes the camera to be lost by the imaging software. This is true of several different softwares I have tried now. 

I have ordered a Simple Handset from AWR to hang from the focuser. The distance is always too great from the laptop to center the image before registering a Sync following a Goto. The IH2 handset now has two cables dangling [now including the ASCOM serial cable to the IH2] so is too unwieldy to take to the focuser. So I have it parked just above and to the right of the laptop. I can run the Simple Handset cable along the OTA to avoid changes in balance. Allowing the Simple Handset to be hung permanently near the focuser and always ready for easy centering.

Yesterday's shopping trip took me past a charity shop. So I nipped in hoping to find a laptop carrying case/bag. I was amazingly lucky and bought a nice bag [in as new condition] for about £4 equivalent. My laptop fits snugly with plenty of padding, rubber feet, loop handle on top and an adjustable, shoulder strap. Large pockets front and back now hold the PS and the mouse mat respectively.

It had become quite a problem carrying the 15.6" laptop and its bulky PS. While walking back and forth to the observatory, in all weathers, day and night. With nowhere to put anything down safely while I locked and unlocked the doors which required both hands. I could only balance the laptop between my feet. Which was hardly practical and easily damaging to the cosmetic finish.

Now I have everything I need in one, well protected, easily carried bag. Handy for climbing [aznd descending] the steep, internal stepladder up to the dome. Rather than balancing the bare, slippery and heavy laptop under one arm. These laptop bags aren't particularly expensive on Amazon but any saving means more funds for something else. The postage alone would have been double my expense for the recycled bag.

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Observatory: Furnishing and accomodation.

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 Using the observatory usefully is now beginning to fall into logical place. The options are really surprisingly limited: Which I had not foreseen.

The telescopes are usually looking upwards from east to west via south. This sets limitations on which areas of the dome are useful and those which are [usually] not. The focuser end of the telescopes sweeps the northern half of the observatory at heights from horizontal and on downwards to the pier as the instruments point higher. At the moment the planets, Sun and Moon are all very low. This will change over time but tends to dominate how the observatory is used.

I do need to make some major changes to my equipment storage now I have a functional observatory. There being no further need to carry lots of loose stuff out to the telescope in the open. Then protect it all from frost and dew usually in the pitch dark. Followed, of course, by packing everything up again even later than I started. When literally everything is covered in dew or ice.

I've tried various storage tubs, including clear plastic, but these are rather vulnerable to knocks. They also offer no mechanical protection to the items they hold during transport. My cheapo, plastic, partitioned, eyepiece storage box is now overflowing with two extra low powers for the binoviewer.

Perhaps I should consider built-in, secure and protective plywood shelves doubling as storage boxes? Nothing wants to be permanently out in the open in case of unexpected rain though the open slit. I have already discovered that any paper left lying on the shelf soon gets damp.

On the southern side the telescopes are usually well above head height and never need to dip downwards. So the southern half of the floor becomes useful as a free area for moving around. It is a safe place to stand to look around the sky through the observation slit for new objects rising in the east. Or sinking below the trees to the west. Though neither view is very accessible due to the height of the bottom sill of the observation slit.

The western side of the observatory is dominated by the stepladder. With its projecting handrails and the large and heavy trapdoor. Or the large and dangerous hole in the floor when open! Now safely lit by a red LED bulb placed inside the hollow pier, 'dog kennel.'

The double door out to the veranda is proving awkward enough in practice not to get much use in the dark. It ideally requires the trapdoor to be down and closed for easy access. Squeezing past the handrails, while ducking down is possible with the hatch open, but difficult in bulky winter clothing.

The doors cannot be opened fully back because of the geometry of the octagon and the width of the veranda. This means they must be closed behind me to use the rest of the veranda freely. Just the price of having no plans and relying on intuition. Once on the veranda the 2' width is fine for one person to move quickly and effortlessly around the outside of the dome.

For the moment I have settled on a computer shelf hanging on the eastern side of the massive wood and plywood pier just above lap height when seated. The AWR electronics are mounted on the southern side of the pier. Well out of the way of moving telescopes and my often clumsy movements in the dark. Though I have added a second red, LED bulb overhead.

The slope of the pier sides would provide ample room for shelves placed near the top. Providing they did not risk collisions with telescopes pointing up high. Since my feet set the limitation on how close I can stand to the pier I would not be likely bump into these shelves or tiered storage areas. While shelves jutting from the octagon walls would be highly vulnerable to my colliding with them in the dark. The pier is easily massive enough not to worry about vibration while selecting eyepieces or accessories stored there.

The overhead red bulb does not spoil my dark adaptation [so far.] It provides a soft flood of deep red light to allow me to safely monitor telescope movement during slews. It also allows me to reach the eyepiece, or change to another, in relative safety. A white light provides a working light after dark if needed to make repairs of adjustments. The cable to the white light must be unplugged to avoid tangles with the dome rollers and steering wheels. 

A chain of dim, red LEDs mark the perimeter inside the dome to help me avoid collisions. I still haven't become accustomed to dome rotation. I always feels as if the octagon and floor are rotating! While the dome is staying perfectly still. Normally I stand still and pull the ribs around one at a time. This is much safer than walking backwards along with the dome until I fall over something.

The red, LED clock is flat on the wall, to my left, when seated at the computer shelf. It is just bright enough to provide some working light when it is dark enough. I wish I could turn off the double flashing colons! Perhaps some black tape would mask them if I applied it neatly.

If I was to offer advice to any would-be dome builders/owners, I would suggest the following: Make, or buy one, at least two feet larger in radius than the horizontal length of their longest telescope. That is at least four feet greater in diameter than the telescope's maximum length including a decent length of dewshield on a refractor. The diameter of the dome is critically dependent on telescope choice. So choose wisely!

I keep finding myself trapped against the dome when I want to look "straight through" the 7" without a diagonal. A diagonal is not always possible when using a binoviewer. It eats up 4" of your focal length in the much the same way as does a diagonal. Using both together would mean chopping large chunks off your telescope tube. Not many people would want to do that.

My 3m [10'] dome is proving much too cramped [at times] when I'm using the long tube on the 7" f/12 refractor. This is largely due to the low altitude of the sun at 55N. I could go back to the folded form but just prefer the conventional tube for aesthetic and practical reasons. Adding four feet or 120cm would mean a dome 4.2m or 14' in diameter. This means a very costly increase in size if you buy a commercial dome!

Unless, of course, you are willing to consider modifying one of the hemispherical, calf rearing shelters. These are of the correct size but heavy and would need a base ring, supporting walls with rotation rollers and an observation slit.

You can't just hack a huge slit out of the GRP dome without serious reinforcement at the zenith and edges of the slit. This reinforcement really ought to be bonded into the rest of the structure for adequate strength. Preferably while the complete dome is erected on a flat surface to avoid distortion when assembled. A curved steel, tubular frame, following the edges of the slit would probably be best. Had I known, what I do now, I would have overcome the weight problem in getting such a dome onto a tall but larger building, using a hired, telescopic loader.  

These domes come in three large pieces. Which helps when lifting them onto the observatory walls.  They are remarkably competitively priced compared with anything on the astronomical observatory market. Though care in modification is essential to avoid disappointment, weakness or even danger of collapse. Still a far cheaper and simpler project than starting to build such a large dome from scratch!

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Sun spotting. Not!

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The promised sunshine has been swamped by fast moving clouds. I was hoping to try my Neximage5 which hasn't seen any action for ages. Venus and Mars were bright first thing [7am] but soon lost to clouds. I wasted hours being teased by cloud for most of yesterday.

More hours wasted waiting for continuous streams of cloud to clear the sun. Had a few short glimpses. No spots visible in white light. Two prominences on the southern limb in H-a. One tall and bold and one much smaller.

I was using Meade 4000 26mm EPs in the binoviewer using direct view at 46x plus GPC enlargement = 50x. This gave me a solar image well within the field of view but still at a good scale. It was very relaxing to scan the entire surface and limb compared with a single eyepiece. It just feels very natural with effortless merging.

I was also very pleased with the results with the pair of 32mms at a native 37x plus any enlargement = 41x. Though the image was considerably smaller it was still pleasant to the eyes. Then I added the 2.8x GPC and enjoyed a huge sun still using the 32mms. Sadly it was a short-lived view because of the arrival of more cloud.

While I was being teased by endless cloud I opened iCap and had the Neximage5 recognized but the menus are microscopically small on my 4K screen! The sun hasn't shown itself since then. If I reset the screen resolution for iCap then it's all wrong on everything else! Grr!

After an hour of solid cloud I was about to pack up when there was a short clearing. Confirmed another prominence at 8 o'clock. Some nice surface texture too before it all descended back into universal grey gloom of a solid overcast.

Just at dusk the Moon popped out from behind the cloud and danced along the ridge of the house. It was so low it actually went behind the chimney. Back to the observatory to have a peek. Rather soft so I swung round to Mars at around 25° high in the SE. I could see it was oval and a hint of a marking but the planet was surrounded in a colourful halo depending on the exact focus.

I have produced a new table of magnifications with the binoviewer's additional 100mm GPL [glass path length.] The binoviewer increases the magnification by adding its own optical length to the raw focal length of the telescope. T-S claim 100mm so the 7" f/12 increases from 2160mm F/L to 2260mm. While the 6" f/8 has a focal length of 1200mm increased to 1300mm.

I need to make some major changes to my equipment storage now I have an observatory. There being no further need to carry lots of stuff out to the telescope in the open and protect it all from frost and dew. Followed, of course, by packing everything up again. I've tried various storage tubs including clear plastic but these are rather vulnerable and offer no mechanical protection to the items they hold. My eyepiece storage box is now overflowing with two extra low powers for the binoviewer. I need to think in terms of built-in, secure plywood shelf boxes. 

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Weekend woes but one bright spot.

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Saturday: Another horribly wet day but with gales. I went up to check the dome and found some leakage around the edges. Fortunately there were no drips. I thought I might find a long strip of aluminium [flashing?] to make a stand up barrier for the top ring of the octagon. It need only be fixed to the timber ring to stop driving rain from wetting the ring on the windy side. The wind drives the rain under the flexible rubber skirt. Something like 6" [15cm] high should help to reduce the draughts and rain incursion. It would be very much easier than building a truly round skirt for the dome itself. Only a few minutes work too. Such a strip could also be added to the 16 sided flashing to make a continuous, rigid skirt in place of the rubber.

Sunday: Grey overcast with occasional light showers but mild. Trying to observe a blank sun but clear views are few and teasing. I had to dismantle the H-alpha scope to tighten the back plate. Managed it during a long cloudy period. So no views lost.

I'm using a 45° elbow for comfortable views. The elbow's longer glass path,compared to the 90° diagonal allows focusing without messing about with extensions or even a focuser. The sag of the hefty, cantilevered H-a optics housings was moving the whole field of view. So I drilled and screwed all the bits together at the backplate. There was no need for the rotation I had built into the flange.

Stellarium is working properly again after a new download of Stellarium Scope! 👍

I find it too hard to find objects without a magnifying glass in Cartes-Du-Ciel despite the zoom. Even stronger reading glasses don't help. This may be due to my inexperience and having a 4k screen on my laptop. I just miss the realism and clarity of Stellarium's rendition and object identification. I don't think I'm going to see the sun for an hour or two! So I might as well find something more interesting to do than watching clouds through the observation slit.

Now I'm back indoors for lunch the sun has come out! I'm looking forwards to accurate Goto slews to the sun. It is so bright that it is often hard to align a telescope by eye. I'm using the finder by placing my hand behind it. When the sun's image is centered in its shadow then the 7" telescope is too. I just have to remember NOT to look through the finder and to fit the full aperture, Baader foil filter on the 7" before I start.

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Mounting: Drives. Ever onwards:

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Thursday: I have been dreaming of push-pull worm adjusters. Some good ideas too, as I tried lots of different layouts. OCD? Probably. Unfortunately my creativity did not extend to reality. The flange bearing housings were much too bulky to allow a straight shot at the motor housings with screws, studs or springs. Which meant considerable extension with metal profiles would be needed.

I'm now thinking more towards small cams to push the motors gently in and out relative to the wormwheels. It need not be as sophisticated as a snail cam or ellipse since the movement required is very small. An offset center pin in a circular metal object will provide fine motion simply by rotation with a spanner or hex key. Once satisfied with the depthing and mesh the clamping screws can be tightened.

I spent a couple of hours playing with C-Du-C. Doing Goto slews between Polaris and assorted planets down near the horizon. Then slewing back to Polaris to see if it could find it again without syncing on the planet. Cartes-Du-Ciel remains reliable while Stellarium Scope now refuses to open. I did get a Scope label on the eastern horizon but I could not 'mark' the map as a target for any Gotos.

Parking with AWR's IH2 handset [paddle] is now behaving itself properly. Which saves me pressing the handset button for several minutes on end. It just needed a proper calibration [Sync] before it would accept parking coordinates. I chose horizontal, pointing east, weights down, for maximum headroom in the dome and when climbing the ladder up to the dome.

I have been dreaming about worm adjustment again. If I trap an offset center, circular 'cam' in a suitable slot it can push and pull the worm and motor assembly relative to the wormwheel. If one end of the motor housing is made into a sturdy pivot then the cam becomes less sensitive. Which is a good thing since it allows finer adjustment. The slot need only be long [oval] enough to allow the cam to turn without binding.

Friday: Still refining the balance and slews but without the laptop. Managed my first Flip after deliberately driving just past the meridian. The handset beeps and warns of the potential mechanical conflict. I repeatedly re-parked the OTA automatically. This all helps to familiarize myself with the handset and OTA movements while it is light enough to see all that goes on. Not to mention avoidance of time wasting when those precious clear sky moments do come along.

OTA clearance from the top ring of the octagon is very even but only about 3" from the star diagonal as it sweeps past the straight sections. Gotos have to be watched carefully because there is always a random element in the routes taken. Sometimes these will sweep over my computer desk/shelf. I may lower the shelf to avoid any chance of contact. So close does the star diagonal pass over. It would certainly collide with anything resting on the surface.

There is always the worry of the OTA hitting my very large pier. I would certainly not trust a remote setup without constant and very clear monitoring from several angles with HD security cameras. Not going to happen. My cable to the Dec drive likes to wrap itself around the mounting so would need very careful monitoring too. Remote working is probably much safer with short OTAs on fork mountings.

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Wednesday: Refractor Collimation continued.

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Wednesday: 34-40F. Clear but with rather a lot of cloud. If that makes any sense. Venus very bright in SE with the fine crescent Moon dragging along behind and lower. Going over for a quick peek as the sky brightens. Or not. Much more cloud crossing now and the sky is too bright to make it worth the effort. So I went for my morning walk. I spotted brilliant Venus even against a light,  turquoise sky with the rising sun in my eyes.

A contact has kindly suggested using a camera and screen to aid collimation. The idea is to watch the changes in the tiny reflections from the objective lens on the nearby screen. As I turn the collimation screws at the other end of the telescope. It being such a song and dance going back and forth from one end of an 8' tube to the other with the big pier right in the middle.

A bit of online research shows that even a cheap webcam will do. If I had one. My Sony cameras stopped working after a Windows update. I could set up my tablet in a handy spot or even the laptop. More on this later when I have something useful to report. Now I'm wondering if an action camera can see through a Cheshire peephole. We shall soon see.

I couldn't get my laptop nor my tablet to recognise the Sony AS15 action camera. So I persevered with collimation without the help of a camera. The thick cross-wires proved to be a hindrance as the reflections neared the center of the lens. However, I succeeded within the limitations of my equipment. The Cheshire is very floppy in every 1.25" fitting I own. The viewing circle can be rocked well over an inch, or more, relative to the objective lens it is supposed to be aligning!

I enjoyed a brief view of the sun between clouds and saw a pair of spots close together. Which I then confirmed in H-alpha in the 6". I tried a range of eyepieces and the binoviewer in between the clouds. I can use the binoviewer without a GPC 'direct' but not in a star diagonal. 'Straight through' is perfectly comfortable in winter but not so when the sun is much higher in the sky.

The house ridge eventually put an end to the fun after suffering a "half eclipse" in the afternoon. I was very pleased at the improvements to image quality. The sun is not an easy target when so low in the sky. Stellarium says the Sun never got above 12 degrees today.

As it became dark I dragged the laptop back out to the observatory to have another go at Goto slewing. Cartes-Du-Ciel seemed very confused and soon stopped slewing over long distances altogether. I went into the AWR Factory menu and managed to reverse both motors under Ustep>RA>Dir and Dec>Dir. After that C-Du-C managed more sensible slews.  I homed in on Polaris after long slews and Synced after an Easterly horizon Sync. I probably ought to add fine, screw driven adjustments in Azimuth. No time to try Stellarium/Scope today.

There is a certain magic about a large telescope moving ponderously across the sky to find the next object automatically. Then to settle over the target with small motor movements to leave a circle over the object on the screen ready to be rewarded with a sync after its warning beep. It's all a far cry from watching a breathless David Peterborough hogging the BBC screen in black and white!

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Tuesday diary: More trials and tribulations.

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Tuesday.  After spending the entire day [yesterday] in the dome working on the mounting and telescope there was a brief clearing after dark. Mars was rising towards the meridian so I had a quick peek. Fuzzy and colourful! The 7" optics were badly misaligned. It soon clouded over again. Putting an end to my misery. Still no AWR-ASCOM Gotos from Stellarium/Scope. Goto slews on Cartes-Du-Ciel stopped working after a while producing only a beep. It thinks the telescope is pointing below the horizon. The Dec drive is reversed and causing confusion. I tried changing Dir in AWR Factory menu but Dec reversal had no effect. I'll have to read the instructions again.

This [Tuesday] morning the sky was beautifully clear and a slender crescent moon was sharing its space to the SE with a brilliant crescent Venus. After having a quick look at an almost impossibly fuzzy moon I resorted to my extended hex wrench to re-align the 7" objective. The cell's collimation screws are buried deep inside the stumpy dewshield. I needed a torch just to see them. There followed half an hour of to-ing and fro-ing from one end of the telescope to the other. 

Shining my torch into one orifice after another, I danced around the pier trying to avoid the junk on the floor from days of mechanical and electrical work and the debris lefty over from the lifting gear. I had to pull each end of the telescope down in turn  just to reach my target. It was impossible to get my head behind the open focuser so I had to resort to a 2" star diagonal. 

I would shine the torch into the eyepiece receptacle to see three tiny reflections from the surfaces of the objective lens. Nothing I tried with the cell's push pull screws made much sense. Eventually the reflection were nearer each other and nearer the center. But only by sheer luck. Repeating a precious change did not improve the original movement of the reflections. So I sneaked a peak at a now badly bleached moon as the sky brightened rapidly. My fiddling with the collimation screws had improved the image but there was still much more to do.    

I need to get more more organized and write down a [long] list of things to do and prioritize my time on improvements:

Collimate the 7" objective and focuser.

Fix the backlash in the adjustment of both worms. I still haven't fitted any screw adjustment and it shows badly on both axes. If I press too hard on the housing when tightening the bolts the motors complain.

Fix a spring latch on the main door to stop it blowing open all the time and making a vertical wind tunnel.

Fix bolts on the shutter doors to stop them blowing open and closed every few minutes. 

Align the 9x50 finder on a much taller stem. Half the field of view is filled with the big dewshield!

Fit some [gun type] sights on the 7" for rapid alignment on an object. 

Improve the white lighting for when I'm working on the instrument in the dark. Or with the shutter doors closed because of rain. 

That lot hardly scratches the surface of things still to do.

_______________________________________

I fixed the finder and re-aligned it with the 7" on a distinctive tree top at 500 yards. Then I collimated the 7" objective and checked it with the Cheshire. The focuser needed some tweaking too. I cleared the floor into tubs and boxes ready to clear it all away in daylight tomorrow.

Tried a number of combinations of EPs, spacers and the binoviewer in H-alpha on the 6". A  nice prominence and a bit of surface texture but no desirable "blemishes" from my swift scan. The blinding sun was scraping along the ridge of the house even from my raised vantage point.

Mars put in an appearance as the sky darkened. Just in time for a string of dark clouds to get in the way. Grr. I'll try again later. And did. The whole sky was now misty and indistinct.

The finder made homing in on Mars much easier this time. Then Mars repeatedly hid behind thin clouds. At full brightness and higher powers it showed an astigmatic colour wash in and out of focus. Red one side and dirty magenta the other. My collimation obviously isn't good enough yet. Given up and come back in for dinner.

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Mounting: Monday build diary. Getting close.

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Monday: Turned a new brass weight on the lathe, then drilled and tapped a 7mm hole in the side. As usual, I used an adjustable furniture foot with M8 thread as the weight clamping knob. With a cut off, plastic wall plug as the intermediate pressure pad. Much nicer than steel-to-steel, the plastic provides a graduated grip. Allowing weights to be slid gently without them flying from end to end of the rail.

With the new weight on the right angle bar, to balance the offset 6" I detached the worms for some careful balancing. The 20kg of counterweights were still slightly too much and would sink to the bottom to the north of the mounting. 

Tying on two 0.5kg [1lb] barbell weights to the far side of the 7" tube rings cured the RA imbalance. Now I just need to fit a screw in each of the spare holes of the 7" refractor's [8"] tube rings. Then I can clamp the small weights neatly and securely.

After that I did some long slews to check if any problems cropped up. They didn't, so I am definitely making progress. Hopefully I can collect all the spare tools and tidy away all the boxes of fixings and cables which have been accumulating on the floor.

Every time I drop something it vanishes through the isolation gap around the pier. To completely disappear into the gravel on the ground floor.

I used a pause in the rain to take some pictures but it hard to get far enough away. I'm using no zoom at all [wide angle.] While holding the camera above my head, with my back to the wall, just to fill the full frame with something of interest. The light is very even when the sky is overcast. There just isn't enough of it to fill the shadows without burning out the highlights.

In case anyone is curious about the long extension tubes on the tail of the 6" this is the spacing before the H-alpha filtering. The filters have to be placed at a set distance from the focus to work at the PST's original f:10. A large, Baader D-ERF rejection filter sits about half way down the 6" main tube to remove [reflect backwards] the sun's intense [and focused] heat and light from the 6" f/8 achromat. Which is working at f/10 with an aperture of 120mm. My trials and tribulations with Solar H-a was covered in the usual great length back in February.

Click on any images for an enlargement.

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Sunday build diary. Balancing tricks.

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Another horribly wet day but no sign of any leaks yet.

Yesterday's additions made the OTA too heavy for 15kg of counterweights. So I added another 5kg weight and it was too much. I am right on the limit with Dec shaft length now. Then I added a c/weight on a bar at right angles to the cradle to help balance the 6" on the other side and to add some weight to help the balance.

Still not enough to balance the RA. I shall have to add another weight to the projecting bar on the cradle. The 6" refractor is far heavier than all sliding weights put together. I still have a lump of brass bar left for a similar weight to all the rest. So I had better get back to the lathe.

Or not yet. I stacked some small barbell weights on the right angle rod to check the total weight required. Overall [RA] and the OTA balance was achieved with 4.25Kg plus the little weight.

A total lash-up but the real weights will be moved to the top of the shaft with a spacer tube below to maximize their effect on the 6". Once fitted they should not affect the RA balance. Only the symmetry of the torque around the Declination axis by counterbalancing the offset of the 6".

At the moment there is still some asymmetry in the Dec/OTA balance. Probably the extra weight of the 6". The OTA still has a preferred poise. Fine when level. Not fine when nose down or tail down. It wants to dive at the low end. I was tying off the ends of the 7" OTA with cords to the dome wheel brackets to keep things safely under control. Having a telescope of this size and weight swinging freely is very risky. The ends move very rapidly quite close to the dome and the pier! It could do quite an injury or damage itself. Better not to take the risk of being hit right out of the observation slit! If it were open.

Talk about sensitivity! With the worms withdrawn for perfect freedom, simply adjusting the focus slightly altered the OTA's balance. Just the price of a long OTA where the distance from the pivot rules the roost. With the worms engaged the friction in the clutches easily absorbs such minor problems. Thankfully, test drive slews were fine.

Another wet and windy day made opening the shutters much too risky just for photography. There were dark spots on the floor every time the shutter  doors were opened. Now I'm worried about spin-drift if it snows! I may need a snow shovel in the dome!

My wife has suggested making or finding a transparent, or glass fronted, protective case for the digital clock. She may be right. I'm not sure how low a temperature such items can stand. A case might slow temperature swings and keep the damp out. A tour of the charity shops might turn up something useful. Or at least provide some inspiration for DIY. No idea what, until I see it.

Click on any image for an enlargement. 

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Big refractor? Fair warning 3.

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A commercial dome, to house your big refractor, is going to cost an absolute fortune! Unless, of course, you have a year or two, the skill and the bottomless purse to put a wooden [or metal] dome together yourself. My 3m [10'] dome is only just big enough for my 7" F/12 with careful positioning. A 7" f/15 would be FAR TOO LONG to fit in my 10' dome. So would a 6" f/15! So be warned!

Remember that a 7" is not even a large aperture telescope. A decent, optimized, 8" Newtonian might be just as good visually most of the time. A 10" almost certainly will be. 

Don't forget to factor in the price of a team of oxen to pull your wooden dome round. Because your leaky, white elephant [sic] will be far, far heavier than you ever planned. Or desperately hoped in your wildest, most optimistic dreams. Just think of the vet's fees and winter fodder for your beasts of burden. Or electricity for the heavy duty motor to drive it.

And no, you can't cheat with a carbon fiber refractor tube. Nor any other of the "magical" modern materials. All the weight of a refractor OTA is in the objective lens. All practical telescope tubes weigh very much the same. Only the stiffness varies, depending on what you can afford. Forget PVC tubes because they WILL bend. Or will soon will if  not already bent before you get it home.

Adding a large, FeatherTouch focuser to balance your heavy objective lens might be a good idea if luck is perpetually on your side. Which means you can afford the hideous expense. I wouldn't want to carry any large and heavy refractor with that much invested in just looking though the thing. A lead weight would be considerably cheaper and far less vulnerable. Particularly when you have to lift the whole thing almost vertically, above your head and onto the mounting unaided. And then back down later in the dark. When everything is quite literally covered in thick and slippery ice! Or were you actually planning to rest your $1000+ FeatherTouch on the muddy lawn? So you can have a desperately needed rest every few steps on your way back to your cramped storage facilities? 

Optically folding a refractor with flat mirrors is very expensive, awkward, fiddly to baffle properly and as heavy, or heavier, than a long, straight tube. You probably won't be able to cover your costs when you get fed up with it.

If it isn't permanently mounted it will be a dog to keep in collimation and no easier to use than the "factory chimney" it replaced. The expensive, flat mirrors will get filthy and will dew up if you are daft enough to leave them exposed in an open framework [like mine]. Capping them securely will help when not actively in use. Just make sure nobody touches the mirrors while the telescope is in storage. Hopefully you don't do any serious woodwork in your telescope storage facility?

The best telescope [you own] is the one which gets used most frequently. From personal experience that means one which is small enough. Or one set up permanently and ready to use at a whim moment's notice.

Comparisons are odious? This is the standard dewshield of a Vixen 90mm f/11 sitting beside the 10" diameter dewshield of the 7" f/12. The 2" Vixen focuser backplate fits the 8" diameter tube of the 7" refactor.

This is a doubling of aperture from a rather modest 3.5" refractor to an equally modest 7". The huge change in scale should help to open your eyes to the reality of owning bigger refractors.

As a footnote: iStar is one of the very few businesses still making objective lenses for private customers. They now offer only "shorter" focal lengths because they get so few requests for standard [classical focal length] objective lenses. They came up with a workaround for this by using heavy flint glass to reduce colour aberrations. My own R35[%] 7" f/12 is supposed to have a correction equivalent to a lens with f/16 focal ratio.

Not having a 7" f/16 to compare the two side by side I must take their word for it. There is certainly very little false colour on the limb of the Moon. It consistently holds double the power of my 6" f/8 Celestron CR150HD. Which I could only very rarely push above 120x to perhaps 150x once a year.

It was quite a revelation to discover that my constantly poor planetary views were not poor local seeing but rather the quality of the objective lens in the Celestron. How else do you explain being able to regularly use over 300x in the iStar?

The view from the ground is very restricted in my back yard/garden because of all the mature trees and ridiculously tall hedges. None of my neighbours has ever shown the slightest interest in clipping our shared hedges. So I had to do all the thankless work. These boundary hedges are supposed to be kept under 2.5 meters but are now over 7-8m high!

Hence the raised observatory. It will only be a matter of time before the hedges win again. The unfinished dome is 20' high in this image taken from the top of the low hill to the east looking west.

 I soon became involved in the building of my observatory so I have done very little observing with either instrument. More often than not they were only half finished or under constant modification.

That said, I was able to instantly see tiny craters in Plato with my 10" F/8 mirror which were always a struggle in the 7" lens. There were not simultaneous views as seeing and [Lunar] lighting might have been the important factors.

I cannot be certain that either instrument was ever perfectly collimated. It was a real struggle lifting down these big and heavy OTAs. Down from the high [above head height mounting and putting them back up again. Not to mention the equal struggle to put them safely into and back out of storage. Which had lower [bare] ceilings joists than their own length. This is not the ideal scenario for maintaining optical consistency! BTW> I'm no wimp despite my age.

D&G used to say that f/12 was very similar to f/15 if length mattered to the buyer. They no longer produce achromatic lenses for amateur customers. Though their lenses have a consistently fine reputation. They were standard achromats so displayed exactly the same colour correction as any other lens of the same f/ratio. Purchaser bias and aging eyes are excellent filters for violet halos.

The message I am trying to get across is that bigger refractors are wonderfully impressive. They do however have limitations. There are those who claim their best views ever [usually of planets] were through a fine refractor.

Hopefully the instruments involved were well and permanently mounted. Such that they could be used often. Rather than demanding enormous willpower to lift a huge and awkward load onto a high mounting. A mounting which can manage a 15" reflector will often struggle with the long tube of a refractor of only half the aperture. Housing the large refractor is a major hurdle to satisfactory and satisfying ownership. Imagine the huge wind drag of a horizontally mounted refractor covered in a tarpaulin!

There are easily available 'props' to judge the scale and weight of any planned refractor purchase or build. Just visit a builder's merchant or big shed DIY outlet which stocks large PVC drainage pipes. Remember to add at least an inch to the objective aperture for the main tube. Otherwise it will be impossible to baffle effectively against grazing incidence just behind the lens. These drainage pipes often come in useful lengths and weights to practice your refractor lifting skills and your own fitness for purpose. Just remember: If you drop it and break it. You pay for it! 

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Big refractor? Fair warning 2.

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Unless you lie flat on a camping mat on the wet lawn you can't usually reach the eyepiece of a modern refractor. Not even with a star diagonal once the telescope tube is vertical. There is a minimum comfortable height of eyepiece for most people even if you lean over. A personal equation depending on your height, build and fitness.

This minimum eyepiece height has to be added to the lower half of the OTA hanging below the massive mounting. Lets assume a normal dining chair height for your personal comfort when viewing vertically overhead. Now measure your eye level above the ground or floor.

Don't cheat! Or it will be a rod for your own back. Now add the bottom half of your OTA's length and you have a minimum figure for pier height on which to plop your heavy mounting. Crane hire, anybody?

6" f/15 = 90/2 = 45" + eye height when seated. 7" x 15 = 105." 8 x15 = 120". That's a ten foot tall tube in old money. Half the tube is 5' + eye height [comfortably seated] is the minimum pier height for viewing overhead with a star diagonal. Your pier should be at least 8" diameter, thick wall tube if it is not to waver. A pier tube of the same diameter as the lens is usually a good idea.

And, no, you can't cheat and use a "faster" f/ratio as the lens gets bigger. In fact you really should go much longer to minimize false colour with an achromat.

It gets much worse with increasing objective diameter and not in a good way. Why do you think they made classical refractors in f/18, f/20 and much longer still? It was not the lack of some magical modern glass. It was basic optics. The science hasn't improved your chances of success over time.

Conrady and Sidgwick are your new friends to avoid certain disappointment. Green means go. Yellow means stop and think seriously before proceeding. Red means you are running a red light while delirious and blindfolded. Your planned kaleidoscope refractor will be dead on arrival and is not to be resuscitated. 👎

If larger APOs weren't so hideously expensive they might be a far more logical choice than an f/20 8".  Even though the large APO objective will be very heavy the much shorter OTA could actually save some money on premium mountings and towering piers for your kaleidoscope big refractor. Aperture counts more than length so just build or buy a handy sized reflector with a quality mirror. 

If you think a cheap, flat roofed, roll-off-roof observatory [ROR] will house your big, shiny new, classical refractor you might be in for a nasty shock. The roof height to cover your ridiculously tall pier, mounting and precious [horizontally parked] OTA might just need a steeplejack.

The roof will probably have to be a pitched but without any cross struts to reinforce your triangles. The roof structure has to safely clear the OTA when it is parked. Plywood triangles with U-shaped cutouts for the horizontal OTA might work. Though at a very high price for materials and weight compared with a conventional timber construction.

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