29.02.2020 Fun with SharpCap and ZWO ASI120MC camera.

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If you find yourself at a loose end, indoors, on a long, rainy day you could play with an astro camera and SharpCap. You'll need the whole sky lens which comes free with some of ZWO's cameras. Though they call it a CCTV lens. Presumably for [wide angle] security purposes.

Unscrew the 1.25" nosepiece and the "all sky" lens flange screws straight into the front of the camera. [Flash image right.] Doesn't the inside of the ZWO 1.25" nosepiece look shiny? Ought it to get a quick flash of real, matt black paint?

By adjusting the front lens ring you can refocus to different distances. Screw the lens ring outwards enough and you can get closer. To act as a magnifying lens. Fingers as broad as your screen! Though you do need enough light. The Gain and Exposure can be adjusted in SharpCap to suit. Now point the camera for a closeup of what you only thought was solid print. The letter from the bank is now full of holes [and spots.] You can play with frame size, as well, in SharpCap. Handy practice to remind you not to capture "full screen" videos with vast file sizes!

Since you have a computer screen showing you the camera's output you may notice a flicker. By adjusting the exposure time you can make black bars across the image of the screen. They will move at different speeds depending on the exposure setting including harmonics. Come closer with the camera and the true texture of the screen is revealed. Lettering on the screen is now more space than solid pixels. It just shows how easy it is to fool the human eye.

The real reason for my experiments with the camera were in trying to reproduce the translucent mask which I see in H-alpha. These make the camera unusable for solar work. Was the ugly overlay an artifact of solar work? The result of using a particular software [SharpCap] on my Laptop? A cable effect? An optical effect? Or something else entirely? I certainly could see nothing amiss in the indoor images using the CCTV "all sky" lens. I had often wondered if the camera's IR filter was "fried" by the heat of my 6" f/8 refractor with its internal D-ERF.

By the way: As I fired up SharpCap today on the 29th Feb. 2020 I was offered a new version 3.2.

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28.02.2020 Nobody knows the troubles I've had..!

Friday 28th: 36-41F. A promising start with almost clear skies and bright sunshine has turned almost overcast by 10:15. Though there are some blue patches coming from the west. Then more cloud, then rain and now sunshine again.

Inside of objective dewed over. Three heat bands set going. New arrangement of PST etalon/filter stack with 2" Ø helical focuser. Direct screw into ZWO Camera by ITF/BF holding adapter. No more need for 1.25" focusing EP holder. The helical focuser does not rotate so the camera orientation remains static. Etalon tuning motor refitted and working.

ASCOM[AWR] and CduC are completely up the creek again! CduC showing 10° West instead of east for obs. site on Connect but East on Set-up. LST 12 hours out on AWR IH2 handset. February 24th? That's four days short of a set! I reset Site, date and time [RTC] on the IH2. Set Home [Park] and it is still slewing to east of the meridian from east side of mounting! Crackers!

Captured a few videos of darker marks on solar surface. Then it rained at 12.50. Now 46F in the dome 40F outside in shade. Lots of huge clouds crossing from NW. Three heater bands have reached 80F but obj. is still steamed up at 1300. Central disk of dew reducing very slowly. I need to wrap the whole OTA overnight and apply a foam dewshield.

13.10 Sunshine returns. Capturing disk videos at 320fps and 390fps. 800x600 & 640 x 480. 6 seconds and 5 seconds for 2000 frames Minimum Gain in SharpCap at 2-1.1ms. Camera temperature climbing slowly beyond 30C to reach 31C max. Falls rapidly on cloud cover.

13.17 Full cloud cover. Lunch! Cue continuous sunshine! [Sic]

14:30 Back in the obs. after heavy cloud and a shower. 

I looked up at the observatory as I returned and could clearly see a large, circular patch of dew inside the D-ERF on the 6" telescope. The three heater bands have been on for ages at 80F. The dome is at 49F with 43F outside.

Still capturing videos while I make fine adjustments to etalon and focus.

It is no wonder the views on the monitor look soft with dark shadows! Dew untouched by the heater bands. I had to remove the D-ERF and blow the back dry with the hairdrier. Half an hour later there was another large dew spot back in the center of the filter again! It's not easy to monitor a telescope pointing up in the air.

What good are the heat bands doing? Were they causing the dewing problem by raising the surrounding air temperature but leaving the [enclosed] glass behind? [i.e. Cooler.]

Saturday 29th Feb: 40F, heavy overcast with steady rain.

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27.02.2020 A few, short, sunny periods.

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Thursday 32F, overnight frost, cloud clearing to sunny periods by 12:00. 40F/44F Out/In dome.

ASCOM AWR driver misbehaving again. CduC showing positive latitude again. Synced to parking place +1° altitude in the east.

6" objective steamed up inside! Have three dew bands on warming. Soft focus with dark blob from dewing on monitor. Cloud streaming across sun's image.

Clear minute or two. 94F at focus without filters but with D-ERF.  59F with KG3 + CCD. Using outdoor thermometer sensor.

It clouded over after lunch so I only started again at about 15:00. Capturing 1000 frame solar videos. 800x600 or 640x480. The image below is my first with the new telescope. Processed in AS!3, Registax6 and PhotoFiltre7.

There seems to be some inconsistency across the image. Perhaps the "sweet spot" for which the PST etalon is well known. I have not settled on a particular etalon tuning point yet. Nor am I sure whether the internal dewing of the objective had completely cleared. I have to remove the D-ERF to see the objective behind it. With three dew bands wrapped around the immediate area it is quite a nuisance.It is probably easier to check for dewing from the tail end. That just requires removing the PST etalon & filter stack.

15:20 Retried the temperature readings despite the sun having sunk. considerably: The outside temp sensor was held against black foam for a minute or more with a sharp solar disk focused. The bright red spot on the black foam persists in my vision for a long time afterwards!

6" f/10 + D-ERF only: 120F!
D-ERF plus KG3 + CCD only 55F.

Dome air temp 43F. Outside 39F in shade.
Checked Kendrick dew band: 88F!
Astrozap: 60F at 12 o'clock on HitechAstro controller knob.

15:25 Clouded over again. Getting cold and breezy as dome turns further towards the SW wind.

Friday: 36-40F. A promising start with almost clear skies and bright sunshine has turned almost overcast by 10:15. Though there are some blue patches coming from the west. Then more cloud, then rain and now sunshine again.

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26.02.2020 Removed 7" from mounting.

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Wednesday: 36F, heavy overcast with light showers and feeling cold. 

I decided to remove the 7" f/12 to leave the 6" H-a telescope on its own. Though I may add the 90mm f/11 Vixen for white light. 

The complete 7" is too heavy to lift out of the rings for my personal comfort. So I used the overhead pulley system. Only removing the 180mm objective once the OTA was resting nearer the obs. floor on a crate. I may  build a counterbalanced, Berry style, fork mount for this telescope. It is really too heavy for the Fullerscopes MkIV.

Following the refitting of the 6"  via its tube rings, I had to add two brass weights to the saddle. This was to help to balance a single, 5kg counterweight and to make the 6" look much less nose heavy. These weights could be returned to my original, sliding weights on rails system, to easily balance the OTA. They could then cope changes like additional dewshield, cameras, etc.

The mounting feels very capable with only the 6" aboard. No overshoot or backlash. Though I still want to hinge and spring load the motor and worm housings into the wormwheels. Still looking for suitable hinges.

The stepladder does fit nicely in front of the veranda doors, as expected. It stands safely upright behind the trapdoor whether it is raised or lowered. The ladder is easily moved aside if I want access to the veranda.

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25.02.2020 Dome concerns and new thoughts.

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Tuesday: 40F, heavy overcast, gales and rain. I shall have to tie down the dome again! Another excuse for working on the telescopes. Or not. It was noisy, draughty and cold up there!

I clamped a laser level onto the dome to see if there was any movement of the red spot on the observatory's far wall. There was, but not much. Mostly slight rotation in fiercer gusts. Little obvious lift. At least, not according to the optical leverage available over this distance. [About 10' or 3m] I decided to play safe anyway and used two ratchet straps to tie the dome down to the massive pier.

With the shutters facing the prevailing wind [SW] there was a fair bit of rubber skirt flapping just below the shutters. Perhaps I should double the skirt just there? It is a short, separate length. The more continuous skirt, on the rest of the dome, is under geometric tension from the nearest sides if it tries to lift.

Brief glimpses of the sun do not tempt me to open the dome in this wind! Normally I'd be out there like a shot! Besides, there are frequent, short showers as well.

The aluminized, foam camping mat has arrived. It looks very smart and practical for DIY dewshield use.

Talking of which: Shiny aluminium would reflect the sky and nearby trees. Suggesting, to me at least, that it would be less visible, from a distance, than a snow white dome.

Would space blankets work to hold solar heat away from the dome? The lightest survival blankets are quite inexpensive. Only one half of the dome needs protection from the sun. Could be doable, but what about the active lifetime in all weathers? The shutters are more easily covered than the trapezoidal panels. Staples?

There might even be a small increase in waterproofing if the material sheds the rain effectively. However, I can imagine it will flap wildly in the wind with being so thin. Can it be tensioned enough to stop it disintegrating? Tape rapidly become expensive, even from just taping the edges over a large area. 

Covering only the shutters has double the value. Or even triple. They would be much cooler when closed in sunshine. When open they shield the dome with their own shadows. If they are also cool from reflective materials, then they have even better value. Cool shutters mean cooler shadows from reduced radiation passing through the shutters to be absorbed by the obscured panels behind them.The panels, which are outboard of those which are shaded, are at a much greater angle to the sun. Meaning less heat absorption. Drawer slides could provide double width shutters on added crossbars. Or the shutters could be made wider to match a wider observation slit. Major work!

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24.02.2020 Undoing the harm?

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Monday too. My old 6" f/8 PST H-alpha telescope had an internal D-ERF. This made converting it to white light use, at a whim, rather difficult. 

My new H-alpha telescope has an external D-ERF. So it could be quickly converted for white light imaging with the Herschel Prism. The internal filters could be removed or simply left in place. The monochrome camera doesn't care [much] what colour it sees.

The reason for this latest rethink? The change in the mounting's behaviour with the addition of the 7" f/12 refractor. It is so long and heavy that it rather dominates the mounting. The 6" F/10 on its own was crisp and completely effortless. It required only one 5kg weight to balance and that was marginally too heavy. So that I added four brass weights to the saddle to achieve perfect balance.

The external D-ERF would need a secure location when not in use. It's removal is simple and foolproof. Three, large, nylon thumbscrews. A slight complication is the dew heater but that is hardly a major problem to solve. 

The tail end would need the PST stack removed. It would be replaced by an empty 2" extension. I could add the helical focuser to obtain extra length without effort and have focusing included. 

Another option would be to have a full aperture Solar foil filter for the 6" to replace the D-ERF. 

Food for overnight thought? I think so.

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24.02.2020 Undoing the confusion!

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Monday 24th 40F, overcast with thin high cloud. The Sun is just visible as a paler "splodge" on the cloud. No sunshine forecast until Friday.

AWR and CduC were both confused on waking up. AWR had gained four days and lost its time by nearly 12 hours!

I reset the time (RTC) and now have LST within + one hour.  I would have to set an incorrect time to achieve a better LST. AWR still thinks I am on summer time! I have reset Dec Direction too. To avoid frequent nose down slews to the sun. Crackers!

CduC now seems to have corrected its Westward observatory siting. Weird, because it showed East in Setup > Observatory but West when I Connected Telescope. Grr?

I had to open up my turned tailpiece, in the lathe, to allow the new, 2" to 2" Baader Click-lock 37mm extension to fit. Which was odd because five other 2" OD extensions fitted easily! I have shortened the screws to allow the new fitting to sink to the maximum into the tailpiece.

The image [above right] shows the bare Click-lock adapter with the filters fitted on the nose. These are lost inside the tailpiece and should protect the etalon and camera. Without the sun's clear, H-a image, I still can't confirm I have reached sharp inward focus. So must wait before shortening the main tube.

My new, 90° elbow, Mini Display port to HDMI cable has arrived. The old, straight mini DP plug stuck right out into the "corridor" beside the desk. The new cable is shown in the image [left.] That's one more problem now solved.

The image also shows the bare clearance of the 7" FT focuser over my closed laptop on the desk during a slew past the Meridian. I need to add some weight at the focuser end to be able to push it higher in the rings! At the moment, I have to dash round and remove the Lacerta 2" Herschel Wedge before a collision takes place! This amateur telescope making and astronomy hobby is a nerve racking business. There's excitement every minute!

Wow! The telescopes actually returned to Home (park) after Syncing on the blurry sun. 13.15pm Time for lunch! Over lunch the sky has darkened dramatically. Even the pale splodge is gone now.

I used a Prussic loop and 3x3 pulleys to drag the 7" tube up through the rings. It would not move with hand power alone. Better balanced now.
 
Connected the dew heater straps and wrapped them around the objective cells. With the Hitecastro 4 port controller set to "ten past" they measured 57F & 58F respectively, relative to 42F ambient in the open dome. Presumably these temperature are high enough to raise the cells and (more importantly) their lenses above the dew point when warmed right through. Though I have no desire to leave the heaters warming overnight.

I am expecting the aluminium coated, closed cell foam, camping mattress roll tomorrow. I shall make dewshields with this material. Promising reduced thermal radiation to the cold night sky overnight. While simultaneously enclosing the heater bands for greater efficiency when warming. At least, that's the theory. 

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21.02.2020 New 6" f/10 H-alpha + Cloud and rain!

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Friday: 38-42F Blue skies! An hour of early sunshine but it is clouding over now. I'm struggling to get an image with the new telescope and the camera. The view through an eyepiece is like tunnel vision. I've dismantled the stack but there is nothing unusual or out of place. Double checked the focus and etalon distance. All seems okay. I'll be trying to view between the clouds now.

The problem was reaching inward focus. With so much cloud racing across the sun I am getting only a fraction of a second of sunshine to make adjustments. With the brightness level all over the place I can't focus at the same time.

I have removed the helical focuser and fitted a shorter extension. I have also shortened the first extension at the back plate. To try and throw the focal plane further out. The etalon group can act as a weak Barlow in this respect. Luckily, I have a 2" x 2" x 37mm long, Baader Click-Lock adapter on order to act as the first extension in the back plate. Otherwise it's a matter of shortening the OTA's main tube. My shortest 2" Ø extension doesn't have a 2" thread for the protective UV/IR blocking filters. Which pushes the etalon outwards if I fit them to the AOK etalon adapter.

Meanwhile the cloud is getting denser and heading for full overcast and even a hint of rain! It is getting windy in the dome now. I might as well give up for today!

Saturday 42F, overcast, heavy rain and severe gales gusting to 60mph. I had better batten down the hatches again. Or, rather, tie down the dome. The westerly gusts were fierce as I secured the dome and mounting with ratchet straps. Prodigious quantities of rain are falling almost horizontally. I emptied my half full collection tubs and covered the mounting with a tarpaulin. Well secured with cords at every eyelet.

The parking space is covered in standing water and the drive is running like a stream! The worst I have seen it in over 20 years. Typical! I secured the observatory in time for the supposed 55+mph wind to drop to nothing and the rain to stop. Sunshine out of clear blue skies anybody?

 I ought to have the ratchet straps permanently stowed on the dome if these gales are to continue for months on end. Not sure, yet, how to store them to follow a concave surface. The pulley system uses screw hooks on the ribs to keep the thing tidy.

Hooking the straps onto eye-bolts at the top of the dome does not easily lend itself to a cleft stick. Keeping even my compact, sliding/telescoping stepladder permanently in the dome is tiresome. I suppose I could support the ladder on hooked brackets on the octagon's top ring. So the ladder stands upright and well clear of the floor. So my huge winter boots can easily negotiate the invisible obstacle when I am not looking out for it. I hardly ever use the doors to the veranda. So the ladder could go at the top of the stairs behind the trapdoor. Providing a further layer of security against the bipedal rodents.

There is the promise of some sunshine tomorrow morning. Will he be able to reach inward focus? Or will he have to re-cut the main tube first? Read tomorrow's exciting episode! 😎

Sunday: 41F. Wall to wall cloud but still no rain by 10.00. It started raining the moment I opened the dome shutters to get more light! I removed the 6" OTA in preparation for fitting the 7" beside it on new crossbars across the saddle. I am using 3/4" multi-plywood, 80mm x 345mm, for the crossbars to save wasting precious, scrap aluminium for the first trial.

The saddle had to come off the Dec axis to drill larger, 8mm, fixing holes for the cross bars and tube rings. I didn't want swarf all over the mounting, RA wormwheel and floor.

I'm going with a 10cm/4" offset for the 7" and just over 6" offset for the 6". 20kg : 12kg. It is important to balance the pair around the Declination axis. By arranging their moments to be equal there should be no asymmetric imbalance. The images show today's progress. I manged to get both OTAs mounted before I fitted the 7" objective. The extra weight would have made mounting the 7' long OTA even more difficult. 

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20.02.2020 6" f/10 H-alpha Pt.3

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I have wrapped an Astrozap, dew heating band around the iStar objective and D-ERF filter cell ready for the next imaging session. Yje three thumbscrews of te filter cell both hindered and helped  The 4-port, HitechAstro dew heater controller is now tied up beside the mounting to reduce the considerable changes in cable tension. Why no tab, screw eyes or hooks for support on these devices?

I'm using black cord to tidy up all the trailing leads. Better than zip ties. Which have to be cut off when they don't suit the occasion. Cord can be easily undone, moved, retentioned and retied as many times as desired.

I plan to make a slip-on, tubular, closed cell foam dewshield, to act as a dual-purpose insulator. This will enclose the heater band to further aid dew removal. The dew heater will not be running when I am not in the observatory. So I will be able to carefully monitor heat build up and its effects on dew removal.

Here's a good choice of camping mat material for a dewshield: The aluminium coating will slow thermal radiation to the cold night sky. While the foam will reduce convection. I like the look of the alu coating and the foam looks rough enough to block grazing reflections. The foam could even be given a quick coat of matt black paint inside if needed.

CAMPZ foam Mat black/alu | CAMPZ.dk

I can slip a thermometer probe on a lead in there. For greater accuracy than my human touch. It is not easy to push a finger inside the taught heater band once it safely tightened in place. Opening the band to check how warm it might be will only increase heat loss.

The D-ERF filter cell has three large clamping knobs. Which would make fitting a metal dewshield slightly difficult. As it would require trimming around these knobs. Besides, a metal dewshield will act as a conductor and draw more heat out of the objective cell and the lens overnight. I shall make a lightweight, insulating plug of foam to close off the dewshield overnight. The nylon threads of the clamping knobs could be trimmed a little to reduce their protrusion. Some sort of glue for the foam would be good to make a much neater job than tape or string. More on this tomorrow.

Thursday 20th 38-44F, Heavy overcast with rain and wind. Imaging looks extremely unlikely. Though such weather can be thought of as a useful goad to making more progress on construction and set-up. It was a horrible day so I worked on other projects indoors.

Possible sunshine tomorrow. But then, they promised sunshine today and there was none.

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19.02.2020 The new 6" f/10 is mounted + first solar H-a light:

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Wednesday continued: 40-47F inside the dome. 40-46F outside in the shade.

I have shortened the collimation "push" screws slightly more to maximize the depth of the D-ERF filter cell overlap on the iStar objective lens cell.

While I had the screw removed I gently brushed the objective inner surface to remove sawdust which had settled inside the OTA. I use a makeup mop for this and wipe the brush frequently on a moist lens tissue. The objective was then carefully replaced using the screws as a guide to alignment.

Once that was achieved I carefully balanced the OTA on a small diameter rod. Then marked the tube's balance point with a magic marker. I also weighed the complete OTA with a luggage scale and found it to be almost precisely 12kg.

The Beloptik 2" UV/IR Cut filter on KG3 has arrived in the post. It has a pinkish hue on reflection but only the slightest hint of light reduction on transmission. It will be used to further protect the PST etalon from heat. The image was taken with flash.

Fitting the new OTA to the mounting took no time at all. The OTA is too light for one 5kg weight but I resisted the temptation to change anything yet.

The sun was out so I quickly re-checked the focus point and the etalon position at 200mm inside focus and had a quick look visually with a 32mm EP. A sharp limb but no detail visible at all. I couldn't adjust the etalon tuning without connecting the drive motor, power supply and the HitechAstro focuser drive box.

Reconnecting the electronics was rather more time consuming. Because I had mixed all the cables together with all the spares in a carrier bag ready for the the storm! I had to replace most of the supplied cables with longer versions to cope with the great length of my refractors.

I was teased with heavy showers and sunny periods all morning. I wanted the bright light from the observing slit to work by. Every time I opened the shutters it rained! No rain was forecast!

Once I had everything connected, Skycharts/ CduC couldn't find the ASCOM[AWR] driver! Skycharts has now completely lost the plot and wanted me to be west of Greenwich. This despite observatory settings clearly showing East!

After manually driving the telescope to the sun it provided a nicely sharp disk with fine surface detail in a 20mm EP. Though only briefly. The image shows the telescope east of the mounting and pointing south west.

Attaching the ZWO ASI174MM camera was the perfect opportunity for the sky to become completely overcast! So no chance to properly check image quality at high magnification! It is now 16:00 and it is getting cold, breezy in the dome and increasingly dark under thick cloud. With another heavy shower as a bonus! Grr!

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19.02.2020 The 6" f/10 iStar H-alpha potential:

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Wednesday 19th: Overcast but some sunshine is promised.

With most of the vital parts now present I can carefully balance the new 6" H-alpha OTA. [Telescope]

The D-ERF and its cell add 1000g right on the nose of the already heavy objective lens in its own cell. The hefty tailpiece I turned, plus the PST etalon and filter stack, will help to balance the nose-heavy arrangement. 

I am still waiting for delivery of the 2" Beloptik KG3 UV/IR filter. Though its slight weight is not going to noticeably alter the balance of the telescope. Nor is it absolutely essential at this time of year. It will earn its keep on long solar sessions when the sun is both "hotter" and higher.

While it is nice to have the 7" refractor available for white light viewing of the sun, moon and planets it is not essential. I keep wondering whether I shouldn't just mount the new 6" for the moment. So I can concentrate on it alone. While I judge its imaging potential and fix any unforeseen foibles. The heavy mounting will hardly notice it is carrying only one instrument.

The new telescope should provide improved views in H-alpha compared with my previous and very secondhand, 6" Celestron. The new iStar H-alpha specific objective lens should be superior in its intended pass band. The native f/10 objective should provide a better match with the PST etalon's needs. It removes the need for the 1.125 GPC.

The new OTA should provide a much cooler instrument. The full aperture D-ERF should considerably reduce internal heating compared to the previous internal D-ERF. The cooler [far more heavily filtered] beam should not thermally impact the PST etalon. They are know to be sensitive to temperature.

Whether a hotter beam affects the air within a solar telescope is a bit of an unknown. Baader claim a cooler OTA when their D-ERF is blocking heat from entering the OTA. Air is transparent and may not know it has a hot or cooler beam passing through it. Usually a target has to directly absorb the sun's focused heat and produce thermal air currents in the internal air.

The glass, optical components are largely transparent except when they are blocking filters. It is possible these can warm and produce plumes of agitated air. The air in the closed tube of a refractor is always considered far more stable than a reflector. Not that this limits a refractor to a closed tube design. Truss and skeleton tubes do exist in both commercial, professional and amateur solar refractors.

That's a lot of "shoulds" but why bother to build a new telescope except to improve my solar imagery? Will any improvements be immediately visible on the 25" monitor screen? Even more importantly: In the final images after processing?

The cost of a 6" commercially produced, H-alpha telescope is at least five times higher than my total expenditure so far. These manufacturers have to satisfy the cosmetic and optical expectations of those able to afford over ten thousand pounds for such a specialized instrument.

Fortunately I do not have the pressure of achieving cosmetic perfection. I only demand optical and mechanical excellence. Time will soon tell whether my own expectations were set too high. The sun has just broken through the overcast to light up the dome! Blue skies are here! See Pt.2:

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18.02.2020 The Baader D-ERF and reworked cell are back!

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Tuesday 18th: 40F, gales and heavy showers.

 Fullerscopes Telescope Mountings: 13.01.2020 160mm Baader D-ERF & T-S filter cell.

I started off by shortening the collimation "push" screws on the iStar 150mm f/10 H-a objective. This was to allow more depth on the nose of the objective cell for the D-ERF holder [cell] to clamp onto. 

The 160mm filter x 10mm thick was a close fit in the holder. It took some time to settle properly into the recess provided. Only then could I screw in the filter retention/ lock ring. Leaving only the hint of a rattle to avoid pinching the precision, optically surfaced glass.

Unlike my 90mm D-ERF the 160mm seems quite symmetrical in its reflectance. With a deep red cast to anything seen through it. Both filters have a penciled arrow to ensure the correct side faces the sun. From memory, the 90mm filter looked much more reflective on one side than the other. I shall have to check this.

The rear of the filter cell is lined to avoid scratching and fits snugly onto the front of the 150mm, iStar, objective cell. With 25.5mm /1" of the objective cell safely nestled inside the filter cell. This is perfectly adequate for security. Though it could be increased further by shortening the collimation push screws by a few more millimeters. The limitation is whether the lens cell is lifted clear of the countercell by the push screws. If not, then no collimation will take place.

The rear edge of the filter cell stops up against the heads of the collimation screws. Which sets the maximum possible insertion of the objective cell.

The telescope, objective lens collimation will be carried out with the D-ERF cell removed. Allowing free access to the M4 collimation screws. Once collimation is achieved, the full aperture filter, in its cell, can be safely replaced to protect the instrument and its user.

The three, large, nylon, clamping thumbscrews provide all the security one could hope for. I was easily able to drag the entire 6" telescope along the bench. Simply by holding the clamped filter cell rim with my fingertips. Under normal circumstances the filter will never find itself "face down."

The 160mm D-ERF filter and its cell weigh almost exactly 1000g or 1kg. The finish of the cell is very satisfying and could grace any telescope without detracting from its appearance.

Different sized D-ERF filters up to 180mm/ 7" and matching cells are available to order from Teleskop-Service. Cells can be made much larger, to order, but Baader does not offer a larger filter than 180mm. Cell manufacture is dependent on purchase of a D-ERF. Though these filters are widely available form other dealers, only Teleskop-Service provide a cell making option. [As far as I know.]

Airies Instruments.Co, of the Ukraine, makes "Triband" ERFs and cells for much larger telescopes and even for SCTs. [Priced accordingly!]

The last images [left and  right] were taken with flash. While the images with the turquoise appearance of the D-ERF are taken in natural light. The colour and apparent depth of the multiple reflections from the numerous coatings are interesting. The depth is only an optical illusion. Not unlike holding two mirrors, facing each other, to see ever smaller reflections going off into infinity.

The purpose of the D-ERF is absolutely vital and will help to reduce the increased heat load, from the large aperture objective [150mm] on the PST etalon and filters. Two further [2" Ø] filters will help the cause by blocking unwanted UV/IR. The PST etalon is normally used with a relatively tiny 40mm objective. An area difference of 12674 mm^2 to 1257mm^2 in the case of a 150mm to the PST's 40mm. An area and heating increase of 14:1!

WARNING! Failing to use a D-ERF on a modified, H-alpha telescope, pointed at the sun, will cause instant blindness of the user at the eyepiece! It will probably destroy the following optical H-alpha components and any cameras fitted at the eyepiece end! 

The D-ERF is a highly specialized [and expensive] filter intended for H-alpha observation and imaging. It still requires further optical components for the telescope to function at H-alpha wavelengths. AND to greatly reduce the heating effect of the focused sun!

Without all of these vital components a telescope objective lens can do considerable damage and cause permanent and devastating personal injury! Building solar telescopes requires considerable knowledge, expense and responsibility. There are no shortcuts! Nor cheap "make-do" components. Take no chances or you will lose your sight! 

For white light, solar observation, with any telescope or binocular, an approved, full aperture solar filter or filters[s] MUST be used instead of a D-ERF.

Leave NO telescope or binoculars unattended in daylight! You cannot possibly foresee somebody unknown trying to view the sun through the telescope or binoculars. Nor do you want to be responsible for "accidentally" blinding your own family members! Warn them repeatedly of the dangers of looking at the sun! Just because it was overcast when you left the telescope "for a moment" does not mean the sun cannot make an appearance!

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15.02.2020 Stormproofing! [Again!]

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Saturday 15th: 41F. Overcast all day.  Another storm is due to hit us tomorrow [Sunday.] I shan't bother to fit the telescopes until afterwards. Meanwhile I can be checking the exact balance points of the telescopes to save fiddling later. It is often a real struggle pushing a heavy refractor up through the rings to find the exact balance point. Particularly when you can't reach the upper rings by several feet. Climbing a stepladder with over 7' of 40lbs of telescope under one arm is an extreme sport IMO. A bit like Highland Games, caber tossing, but practiced indoors in a rather confined space!

I have "storm-proofed" the dome with four ratchet straps from the zenith board down to the pier. All the electronics have gone into hiding and the mounting covered in a small tarpaulin. The shutters are facing SSW. Last week the weather forecasters said storm Ciara would blow from SW but it blew only from the south. So, this time, I am aiming for  halfway between South and Southwest.

Sunday 16th: 51F! Spring temperatures! Gales from the south with very strong gusts and showers. The trees behind the dome are rocking as the wind roars outside my rain-spattered, north facing, dormer window. I haven't been over to check the observatory. Because I don't want to frighten myself! 🙄 It can get a bit noisy in there in a gale. Besides, I don't want the wind blowing though the south facing door and inflating the dome! The worst gusts should be over this afternoon but will return again tomorrow.

Another storm survived. The wind was already dying down when I went over to check for rainwater in the sandwich, collection boxes on the base ring.  I really ought to attend to the shutters. I made them slightly too wide. Which means there is a ventilation slot of about half an inch, on either side, from top to bottom when closed. Which is fine for adding to the dom'es ventilation to avoid overheating.

Facing the shutters into the weather is causing more rain ingress than is desirable. I suppose I could try self-adhesive, foam strip. The alternative is to cut away a strip from top to bottom of the plywood, shutter covering. I'd gain an inch of shutter opening that way.

Or, arcs of plywood could be glued to the insides of the shutter rib to close the gaps. That would also help to stiffen them. Possibly making the closing of the shutters slightly easier. Holding the arcs in place while the glue dries would take some ingenuity. Though the arcs could be made wider to allow easier access to fixing screws. I'm trying to think of an easily removal sealing strip. To allow ventilation when there isn't a storm blowing!

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14.02.2020 More checks and balances:

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I re-weighed the complete OTAs today:

The 6" weighs 9.5kg without the PST stack and D-ERF fitted. The PST stack weighs 1100g.

So that's 10.6kg total + the D-ERF & holder. Probably another 1.5kg at a guess.

Plus 0.5 kg for the tube rings. Say ~13kg in total? Quite a hefty OTA for a 150mm/ 6" f/10.

EDIT: The complete H-alpha 6" OTA weighs almost exactly 12kg with D-ERF and its cell.
I intend to add a dew heater band and foam dewshield but these weigh very little.
The figures below will be changed by making the 6" equal to 12kg.

I still need to order some shorter, M4 stainless steel screws to replace the temporary screws holding the OTA together. Stainless steel fasteners are smarter and don't rust within a week of purchase. I see the nuts on the brand new Skywatcher tube rings are already rusting! They haven't even been used yet! This is unforgivable for a commercial product expected to be exposed to the weather, thermal cycling and dew. Penny pinching gone raving mad!

Meanwhile, the 7" main tube + focuser weigh 10.65kg.

The tube rings are 2kg + 1kg for the 2" solar prism.

So that's 14kg + 5kg for the 180mm objective = say ~20kg total!

Difference = 20:13. So the balance of the two OTAs [placed side by side] on crossbars, mounted on the saddle, needs some reworking since my last post on the subject. 

20kg x 4" offset    =  80 kg/inches moment. [4" = 100mm]
20kg x 3.5" offset  = 70kg/inches moment. [3.5" =89mm]
20kg x 3" offset     = 60kg/inches moment. [3" = 75mm]


80/13 = 6.1 inches  offset [6" OTA] 
70/13 = 5.4 inches  offset [6" OTA]  
60/13 = 4.6 inches offset  [6" OTA]

The C of Ms of the two OTAs can be offset from the saddle center line/declination shaft by these ratios. Depending how far apart the OTAs need to be to avoid obstructing the hinged tube rings as they are opened and closed. Placing the thumbscrews between the OTAs solves the ring/tube collision problem. At the cost of being more difficult to reach.

See images. Offsets not to scale but merely for illustration.

Counterbalancing: Both OTAs together weigh 33kg. The offsets from the PA relative to the center of mass of the counterweights is roughly 40 : 55. [1:1.375] So the CWts have the leverage advantage thanks to greater moment. 33/1.375 = 24.

Five x 5kg counterweights should balance both OTAs with enough spare to add sliding [tube balancing] weights on the OTA side. The 5kg weights are 1" thick so need only 5" of Declination shaft free. The counterweights can be adjusted along the shaft for final balance using spacers. Provided the mounting can manage 25 + 33kg = 58kg. I have had three telescopes at a time so have already proven the load capacity. Four weights could be moved to the far end of the Dec shaft if so desired.

Saturday 15th: Another storm is due to hit us tomorrow [Sunday.] I shan't bother to fit the telescopes until afterwards. Meanwhile I can be checking the exact balance points of the telescopes to save fiddling later. It is often a real struggle pushing a heavy refractor up through the rings to find the exact balance point. Particularly when you can't reach the upper rings by several feet. Climbing a stepladder with over 7' and 40lbs of telescope under one arm is an extreme sport IMO. A bit like Highland Games, caber tossing, but practiced indoors!

I have "storm-proofed" the dome with four ratchet straps from the zenith board down to the pier. All the electronics have gone into hiding and the mounting covered in a tarpaulin. The shutters are facing SSW.

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14.02.2020 6" f/10 H-a first [white & red] light. NO SUN!

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Friday: Having fitted the baffle tree and replaced the heavy tailpiece I could fit the iStar 150/10 H-alpha objective.

By sheer luck I found the focus suited the empty fittings for the PST H-alpha stack. [Image right]

The second [lower] image shows the full H-alpha stack.

The OTA was simply propped on a folding workbench with G-cramps for safety barriers against rolling off. There was some peripheral [blue] colour from zooming in Macro on my old TZ7 camera. I cropped this out of the image because it was invisible visually.

A 32mm EP provided a very pleasing views of 600 yard distant trees at 47x with little sign of false colour. Visually, it looked much brighter and sharper than this cropped, zoomed and enlarged image.

At 75x [20mm EP] the image showed some royal blue, false colour. It is a dark, overcast day. So this should be allowed for in the [through the telescope] images.

Image right: The same set-up x47 but with the Baader 35nm CCD UV/IR filter fitted. Macro zoomed TZ7 camera. A Beloptik KG3 will join it to further protect the PST etalon from the heating effects of the 6" objective.

A full aperture 160mm Baader D-ERF will sit in front of the objective lens.  Until I have the D-ERF fitted, I cannot try the telescope on the non-existent sunshine. Teleskop-Service has just rung to confirm the D-ERF filter and holder are going into the post. Delivery is now expected on Tuesday 18th Feb.

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13.02.2020 180mm refactor, FT focuser adapter and backplate.

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Thursday 13th: Spent some time "playing" with the focuser backplate of the 7" refractor. I had a threaded ring, focuser adapter made by Teleskop-Service. It works fine with the FT focuser. Though getting the clamping and friction levels correct has taken a lot of time. It relied on the thickness of the backplate for proper clamping.

I finally got rid of the springs. Which I have always used for focuser collimation on the 7". Springs simply didn't work no matter how stiff they were. They always ended up squashed flat or floppy. I just didn't have enough thickness in the backplate for threaded holes for collimation, "push" screws.

Now I have replaced the springs using nuts as spacers. These are placed on the long screws which hold the back plate onto the main tube. I added a combination of roofing washers and rubber tap washers. The latter are used as sliding friction devices for adapter ring containment. Otherwise the spacers and retaining washers can fall off, out of sight inside the backplate, without my knowing.

The focuser now turns correctly and is finally rock solid. No more shake. I should have bought an official FT adapter when I bought the focuser. But I just could not bring myself to spend so much. Besides, none of the available FT adapters really suited my needs. Another and convincing reason not to waste hundreds of £ounds equivalent. A simple flange adapter would have been good but require a whole new backplate. Instead of the saucepan base I have used since building the refractor. In reality I should have found another saucepan. One with a much sharper curve between the base and sides.

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10.02.2020 The aftermath of the storm.

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Monday 10th 43F. The aftermath: My anemometers are hardly turning this morning and the trees are quite still for most of the time. With occasional rocking to violent gusts. The wind was highly variable for the rest of the day. Alternating between noisy and powerful gusts and relative calm.

I spent the morning undoing all my paranoid changes in the observatory in readiness for yesterday's  storm. Not too much collected rainwater in the sandwich boxes and the observatory floor and desk were completely dry. Thanks to the shelter belt of trees to the west it was mostly, quite peaceful in the dome today.

I did some calculations to try to work out the thread used on the Beacon Hill worm drives. No standard thread reared its ugly head, but M27x3 would match the smaller wheel. While 1" BSW worked close enough for the larger. These are only guesses and may be in error if the machinist used his own pitches rather than hobbing.

I sprayed the previously hand painted, baffle tree with matt black paint. Just to fill in the bare streaks from the cheap paint brush I had used earlier on the water based paint. I did the spraying outside in the lee of the workshop. To avoid inhaling the strong, petroleum fumes without spraying into the wind.

Next I painted the plywood countercell of the new, 6" H-alpha telescope. Otherwise it might never be done. Just like the 7" cell wasn't painted until very recently. The appearance didn't really bother me too much. It just looked a bit sad, amateur and unfinished in the photographs I shared online.

Both counter-cells are now painted matt black to match their lens cells. I also sprayed the inside of the 6" main tube from both ends. Also the inner face of the heavy tailpiece I had turned in the lathe.

After that I finally sawed off the spare [unused] crank on the top dome drive sprocket. Then turned the sawn crank stub smooth and round on the lathe. Slowly and gently, to avoid the hammering of the highly eccentric work piece.

I added two timber packing blocks under the [lower] drive crank support plate to stiffen it up. It feels much better as the crank is turned instead of being a bit floppy. Having tested the result I shall make a smart, new, single, packing block from larch cut-offs. With matching holes bored for the crank plate fixing screws and the [bicycle] bottom bracket axle.

The counterbalanced, friction wheel drive has worked well beyond my expectations. With a perfect [gear] ratio between speed of dome rotation and almost effortless cranking. Instant change of direction too. With easy acceleration up to speed for a rapid change of shutter orientation. Or just crawling around as required.

The secret to success was placing the friction wheel on the short end of a long "seesaw."  With a 5kg weight on the far end to provide plenty of self-adjusting, upward pressure at the friction wheel. A fixed drive wheel would never have worked without a perfectly true base ring. While too much vertical movement would have played havoc with the chain drive. Which I added later to bring the crank down to within easy reach. While seated at my imaging, computer desk.

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9.02.2020 Storm Ciara!

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Sunday 9th 41F: So much for trusting the Danish national weather service! I deliberately rotated the dome to face SW. The DMI shows south westerly severe gales all day. When the wind has been steadily, unchanged from the south. My sensitive wind vane is spinning like a top at times but never points steadily to the SW.

The independent TV2 station shows southerly gales until 7pm when it peaks and turns SW. I am watching the dome and the rubber skirts are rippling on the angled sides of the octagon. Presumably from updraughts from the observatory walls. While the southerly skirt is flattened against the base ring. I'm glad I left the inner plastic skirts in place. They prevent most of the wind getting in under the dome. Though I wish they weren't rippled. I used recycled plastic, lawn edging. I never found any other stiff-enough material, in sufficient width and length to be useful. It has to stand up on its own even in a gale.

Top wind speed today [Sunday 9th February] from storm Ciara, according to the Danish news, was 83mph in eastern, Southern Jylland. My dome is still up there. Though I shall have to wait until tomorrow to go and empty the rain collection tubs on the base ring. About 3/4" of rain was forecast for today.

Strong winds are still expected over the next few days. The storm is over 4000 miles across. Reaching from Florida to Scandinavia. British newspapers are describing it as The Storm of the Century. Several rungs down in media importance from the best and worst Oscar dresses! Yawn.

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8.02.2020 Storm Ciara due tomorrow!

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Saturday 8th 41F. A storm, with powerful winds, is forecast for Denmark tomorrow afternoon and evening. With 60+ mph gusts promised for our area.

So I have taken the remaining telescopes off the mounting and stored them safely. The dome has been cleared and the shutters have been rotated upwind to the SW. Where the worst wind is forecast by the DMI.

The dome shutters now have eight, spaced spring clamps right up to the zenith. Two G-cramps are helping to hold them firmly shut apart from the usual, sliding door bolts at the bottom.

I have secured the top of the dome down to the massive pier using long, ratchet straps. These were hooked between heavy eye-bolts fixed through the zenith, triple thickness, dome cross-board. With the ratchet straps running down to hooks under the 18mm/ 3/4" cladding of the upper, telescope pier. 

The heavy mounting, plus 56' feet of 4x4" pier timbers, plus 3/4" cladding, plus four, buried, pyramidal, concrete, carport anchors will take quite some lifting! So I hope the dome itself will now be completely safe from lifting. It already has eight, permanent disks overlapping the base ring. The disks are mounted on the steering wheel brackets held down to the octagonal building's, 2" x 8" top ring. So the ratchet strapping is really just extra insurance.

Domes are not renowned for lifting but can burst open. They have no horizontal surfaces to cause lift. The worst thing which can happen is a dome opening up so that it can be inflated by the wind. This will be likely to blow panels off the dome leading to serious failure and damage. Hence the deliberate, upwind direction of the shutters. Rather than risking them being ripped off by downwind suction.

Somebody online had their entire dome fly off the walls when they [foolishly] opened the doors facing into the wind! I am glad my access doors face south and I can enter the dome from below. It wouldn't be half as much fun to enter from the veranda doors which face west. I only open one half of my double doors on the ground floor. The potential is there should I want both doors open but there is plenty of room to get in via one.

I have now cleared the observatory of all loose items and covered the big mounting with a giant, leaf collection bag. I don't mind if it doesn't blow remotely as hard as forecast. I haven't lost anything by being prepared. We suffered some roof damage in a "once in a century" storm about 20 years ago. So know the power of the wind. Better to be safe than sorry. I can potter around today. Ensuring everything is as safe as possible before the wind picks up.

There is nothing downwind except trees, fields and forest. We are protected, to some extent, by a shelter belt of trees to the west. Though this belt does not extend quite far enough to the SW. Which leaves us potentially exposed. Thankfully our own garden has been much better furnished with trees and bushes to the SW over the 20 intervening years. Though the boundary trees look a bit tall and spindly in their bare winter clothing. They should all help to take the edge off the worst gusts.

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6.02.2020 More D-ERF woes!

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Thursday 6th. Overcast.

The second example of 160mm D-ERF filter holder [cell] has arrived from Teleskop-Service. Unfortunately their machinists are still ignoring my exact instructions on internal dimensions.

Yet again they have made the front recess 160mm diameter instead of the required 161mm. So there would zero clearance for the 160mm glass filter!

The upside is that the rear recess has now been enlarged so that it now fits onto my iStar objective cell perfectly.

The 160mm filter holder [cell] weighs 550g. The filter cell is beautifully made and appears flawless. Note the protective lining felt and nylon screws to protect the glass filter and the telescope onto which it fits.

Once the filter glass is safely housed in its cell, when it actually fits, the total weight up front will be over 1kg. The 160mm Ø x 10mm thick D-ERF filter is a substantial lump of glass. My D-ERF is still with Teleskop-Service because they asked me to return it, with the original filter cell] to ensure they fitted each other!

Now expected to return the second holder for further correction.  Five weeks and counting, since my original order was accepted.  🙁 31.12.2019! Grr? Filter cell returned to Teleskop-Service this afternoon.

Friday 7th, 41F. Another overcast day. I tightened all the nuts on the baffle tree to make quite a rigid structure. After checking it would slide easily inside the main tube I removed it again. Then I painted all the baffles matt black with water based paint. It's a bit cool for paint but hopefully it will dry. I didn't paint the studding because that would make the nuts immovable if I ever want to dismantle the baffles.

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5.02.2020 More balancing tricks leave me baffled.

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Wednesday 5th, A frosty start with a clear, sunny morning promised. I still don't have a useful telescope set up. I don't want to struggle with mounting the 7" just for one morning's white light. It would only have to be removed again as soon as I have the 6" completed. 

EDIT: Ignore the following figures: I weighed the components of each refractor. The 7" weighs 16kg plus 5kg for the objective. While the 6" weighs 12 kg plus [say] 1kg for the D-ERF and holder but including the PST stack. The image [above right] shows a full scale mock/up using their present weights and moments. 16:12. The 6" can still be moved in enough to compensate for the extra weight of the D-ERF at 16:13kg. There is no need for the C of M of either telescope to fall outside its own diameter on the crossbars.

The weights of the pair of completed OTAs, mounted on crossbars, is close enough. Only their dewshields need some space between them to achieve sufficient offset.

I was able to purchase four 1m lengths of M4 studding. So I can finish the baffle tree tomorrow.

Still waiting for confirmation of dispatch of the D-ERF and holder ring from Teleskop-Express.


It is quite amazing how new ideas crop up when you follow a link online. Not necessarily anything to do with the original subject matter. I found a new idea for hinging and spring loading the worm housings. Not with a single pivot pin but with the whole motor and worm tilting into the wheel.

If the assembly is mounted on a flat bar the rounded edge can pivot in a rounded slot. With excellent constraint against end play [or backlash.] Previously, I was seriously considering using a heavy [probably brass] door hinge. Which would have multiple resisting surfaces against end play. The hinge would need to be very stiff to avoid twisting in use.

My box section, worm supports and motor housings can be seen to flex very slightly when I move the telescopes manually. This would be unlikely to occur during normal Goto slews but might be a hidden issue in tracking. I like the idea of spring loading the worm into its wheel. It avoids potential concentricity issues.

Having had to make bushes, to reduce the supplied wormwheel bores, to match my smaller shafts, it has always stuck in my mind. Though a single pivot pin is not ideal. Longitudinal forces or resistance would tend to wind the worm out of mesh. I think this would be less likely to occur with a linearly hinged system because the pressure is spread across the entire face of the worm.

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6" H-alpha OTA: Baffles:

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Tuesday 4th Feb. 38-41F, cool, but bright start, then dark overcast, then bright again.

The difference in scale between a 180mm [7"] and a 150mm [6"] objective and their respective cells. The 7" looks opaque due to misting over after a night in the cold observatory. Then being brought out into warmer, outside air. The same sometimes occurs when I open up the dome to sunshine after a chilly night. Hence the recent investment in dew heater bands. Clear skies for observing and imaging are far too precious to be lost to dewed optics!

I have found some scrap, aluminium roof flashing which could be used to make the baffles for the new 6". Metal baffles are always advisable for a solar telescope to avoid the risk of fire. 

I clamped two planks on the portable bench jaws with a tapered gap between them. This was to represent 150mm at the wide end and 60mm at the backplate/tailpiece. 

A quick guesstimate suggested the 115cm total length should be divided into 5 baffles at 20cm spacing. The baffles would be just under 160mm in outside diameter to fit comfortably, square-on, inside the main tube. The first baffle behind the objective lens ought not to be made too narrow. This isn't a real problem with an oversized tube. 160mm tube to a 150mm lens. There is no grazing incidence on the undersized tube just behind the lens. 

I used the tapered planks to measure the gaps between them at the marked baffle positions. 135, 115, 100, 85 and 70mm in series. The numbers were then drawn as a series of circles onto the metal sheet with compasses. With outer circles of 160mm using the same, center-punched centers to ensure concentricity between the circles. 

The outer circles were cut out first with ordinary, straight cut, tin snips. Followed by drilling a short chain of holes in each inner circle to allow smaller, curved jaw, tin snips to get a start in the metal. I then cut out the inner circles to make the baffle rings while wearing protective, rubber gloves. Quite a lot of effort is needed for the curved cuts and the grippy gloves really help here.

I smoothed the outer circles with the 12", bench, disk sander. The inner circles were smoothed with a "half round" file. Finally I flattened the baffle rings with a weighted plastic hammer using a block of wood as an anvil.

The next step is to stack and then drill all the baffles identically near the periphery. These holes are for small diameter studs [threaded rods] to hold the baffles at the correct spacing. Pairs of nuts will be run down the studding to hold each baffle in place. I find a rechargeable drill to drive the threaded rod makes quick work of this. Each pair of nuts being left loose until they are all roughly in place.

 I need to buy some studs from the nearest builder's merchants. Followed by painting the completed baffle assembly with matt black paint. The friction of the baffles inside the tube is usually enough to hold the whole baffle "tree" safely in place without any fixing.  I used exactly the same baffle construction system in the 7" f/12 refractor.[Image: Right] Thought the 6" will only need three studs thanks to the shorter overall length.

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