Heavily modified Mk111 for sale

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A contact has kindly shared the sale of a rather sophisticated Fullerscopes Mk111:

Scroll down until you find Fullerscopes in the item sales headings:

 http://www.presencenet.be/nucleus2.0/?catid=5
 
I think you will agree that it represents a remarkable upgrade on the original mounting.

The stand, with levelling feet,  is no doubt lighter than Fullerscopes own. It includes telescoping height adjustment for observer comfort with different instruments. The long, triangulated feet should provide good stability.

30kg load bearing capacity is claimed.

Large setting circles are provided.

A sturdy dovetail unit looks capable of firmly holding relatively large instruments.

The seller lists an 8 1/2" [220mm] RA wormwheel. While the Declination axis has an 8" [200mm] wormwheel. Both wheels are made of bronze for long life. As were the Fullerscopes originals but which were only a, relatively tiny, 3 1/2" in diameter.

These enlarged wormwheels should offer far more accurate guiding and slow motion control of heavier payloads.

Note the use of stepper motors in place of the original synchronous drive motors of the original mounting. The shafts have been increased to 28mm in place of the 25.4mm originals. The brass rings may indicate improved bearings.



The Fullerscopes head castings have been smartened up. It is  matter of taste if you prefer naked metal or different paint finishes. Fullerscopes offered the same choices.

A small turnbuckle provides fine adjustment and stability in polar altitude.

A modern hand paddle to control the mounting via the stepper motors.


The whole mounting seems to have been modified. Providing plenty of inspiration to those seeking a strong alternative to the commercial mountings available. 

Click on any image for an enlargement.

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10" f/8 Moon and Jupiter Pt.2

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While playing about with the collimation in daylight I discovered the secondary mirror was rattling and rotating in its mounting tube. So I cut a piece of soft foam to stuff behind the mirror. One less thing to worry about.

Next I removed the primary, removed the fan from behind the mirror and fitted it on the back of the cell. I then added another spring to each collimation screw and added a washer under each wing nut.  Now adjustments were firm and without backlash.

Having tilted the OTA gently upwards on the bench I inserted the Cheshire alignment tool and re-collimated from scratch. Looking from in front of the OTA past the secondary was the easiest way to get rough alignment. Finally I had everything overlapping as seen through the Cheshire.

The Moon was climbing over the hedge as I put the OTA on the MkIV mounting and connected the drive box. Now I could see two tiny craters in Plato and lots of shading in the relief of Plato's  floor. Turning on the fan only caused vibration without any improvement in seeing fine detail.

Jupiter was still soft despite being high overhead. Worse than last night.

Dinner over and now I'm going back out to try and get some handheld snaps with the Canon (short zoom) digital camera. The best of my results can be seen above. After I removed the rubber eye cap from the 20mm eyepiece my simple tubular camera adapter was much too loose. It used to fit my missing, rubber clad, 20mm no-name Plossl perfectly. I believe the eye relief was also better than the 20mm Meade 4000. This sloppiness in the adapter needs more work in daylight to ensure effortless centration of the image in the camera field. The 20mm provides 100x visually on the 10" F:8.

My guess as to the Moon's altitude was wrong yet again. It had only reached 45 degrees on the digital clinometer when I finally packed everything away.

Click on any image for an enlargement.

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10" f/8 March madness on the Moon and Jupiter.

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Clear skies and the Moon sharing the sky with Jupiter high above drove me to get the 10" F:8 out again. Clear skies with bright moonlight and no wind at all are very unusual.

I fiddled about with the collimation until I could use 200x on Plato. I was able to glimpse the central crater at all powers from 100x upwards. I even ran a long cable out to the (noisy) mirror fan from a 12V model train transformer. It made quite a racket at first but then settled down. The fan was blowing forwards around the mirror from the rear opening in the cell. I cannot say that it made any other visible difference except applying micro-tremors to the image. I tried reversing the polarity but the motor would not start. I need to look into this problem in daylight. Reversing the fan physically within the cell is not an easy task since the primary mirror has to come out.

My larger collection of Meade 4000 eyepieces seem to be anything but parfocal across the range. They have a mix of "Japan" and "China" markings so that may be the cause. As I didn't need to be dark adapted for the Moon or Jupiter I used a diode torch to select eyepieces from their new case. Which I had placed on the mounting base slab under the angle iron stand.

I have added 10mm closed cell foam to the little partition boxes to raise the eyepieces to an easier level for removal and replacement. The partitioned boxes were too small to allow any more foam to nestle the eyepieces properly. I don't think  this matters too much since they are not subjected to long journeys in the car. Thanks to the handles moulded to both top and bottom of the the case it is very unlikely to be lifted in any way which would tip out the contents onto the ground.

The range of powers has been re-ordered to make selection easier in the dark. Lower powers to the right. Higher to the left. The hinged lid is handy because it drops down automatically to protect the eyepieces from dew. Not bad for under £3 equivalent. Using a very deep, padded box, with the eye lenses facing upwards, doesn't make much sense to my fuzzy logic. I can use the comparison of length to sort them easily and quickly. The Dyno tape markings on the lid are easily read with a torch to confirm which power I am using. It is very easy to see which lens is in use from the empty partition. It would have looked tidier if there were far more partition options but beggars can't be choosers. Having used a deep, plastic storage box for my eyepieces for years I much prefer the new arrangement. All the extra space around them makes them easier to lift out and replace in the dark.

I struggled again to focus quickly and accurately with the simple Vixen focuser. Since I wanted to avoid physically exciting the OTA with my focusing efforts it required great care not to shake the desired object out of the field of view. I can now see why slow motion knobs are so popular. The rack and pinion focuser does not offer the tiny adjustments or sensitivity in focus required at higher powers.

Despite being F:8 the telescope is either in focus or it is not. There is no "refractor like" softness in best focus. The greater flexibility and leverage of such a long OTA does not aid focusing when the image has to "die down" between every touch of the focuser knob! Focusing was far easier on the Moon than Jupiter. Jupiter had four moons on one side. With two moons very close together which changed rapidly in the two hours I was out there. The moons themselves looked like kids (poor) drawings of stars. So the collimation was still way out. Jupiter defocused to into a triangle of three offset blobs! Though I could still see some detail in the belts.

The mirror cell continues to irritate with its sloppy and sticky collimation adjustments. Undoing a wing nut almost guarantees it will go slack. Trying to tighten one often feels as if it is fully tightened. The spring pressure is probably just not enough to support the weight of the primary mirror. Last night's observations were cut short by completely losing the collimation while trying to fine tune it!  

I have promised myself that I would solve the mirror cell collimation problem but haven't. I haven't fixed the flexibility of the mirror cell pot either. There is always an element of inertia to completely undo previous construction and start again with a potentially better design. As the Irish are supposedly fond of saying: "I wouldn't have started from here." 

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10" f/8 Jupiter & M42.

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Jupiter was already at a good height when I trundled the tube out to the MkIV mounting on the lawn. The problem is that every such journey throws the collimation out again. I tried inserting the Cheshire eyepiece but it isn't easy to use in the pitch dark even with a diode torch. Alignment was well out and the curved vane secondary holder and my rather clumsy mirror holder really don't help.

I have bought a dirt cheap storage case for my enlarged selection of secondhand Meade 4000 eyepieces. Simple Dymo labels on the lid show the power in the 10". I am experimenting with foam padding but unhappy with results so far. These are a mix of Japanese and Chinese made Meade lenses. 32, 26, 20, 15, 10 and 6.4mm are now present. The 2x Barlow provides intermediate powers if desired.
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Eventually there was reasonable optical alignment and I could try the telescope on Jupiter. Though the two major belts were clearly seen there was little extra detail. There was the usual drama of trying to turn the focuser knobs while the image shook. The 10" is a real jelly compared with the 6" refactor. The latter is rock solid on the MkIV mounting.

For the next couple of hours I tried a number of eyepieces without improving the quality of the image. I had connected the power supply and paddle to the drives though I made little attempt to align the polar axis. It was pointing roughly north and that was all that mattered for following a planet for visual use.

Then I tried the telescope on Orion's Nebula M42 and was astounded at the detail visible using 32mm and 26mm Meade 4000  eyepieces. The 26mm was best at 77x for its improved contrast with the darker sky.  I felt I could actually see the wavy surface of the nebula. The gas clouds stretched to the edge of the field of view with deep black notches and widely extended wings. Better than I ever remember seeing it before in any instrument. This was despite the rather low altitude of the nebula. Dark skies obviously help here. 


Note the coincidence between spaces available and components to be fitted. Unfortunately there is no real choice as to where the yellow spacers may fit. So there is a little too much room in some places. An Orion 2x Barlow sits at top right alongside the Cheshire collimating eyepiece. The simple digital camera nose/eyepiece centering adapter is the bright blue object sitting at the bottom left. 

The intensely bright ISS went over at one point. I watched it through my 10x50 Zeiss binoculars but no detail was visible. A surprising number of satellites passed through the field of view wherever I was looking with the telescope. It must be getting quite crowded up there!


I retired indoors for dinner at 8pm and returned an hour later to much mistier skies. Finding a bright star overhead, I tried racking through focus to compare the infra and extra focal images. At least they were similar, round and fairly sharp edged. Orion had disappeared behind the roof but Jupiter was now very high.

Unfortunately the image had not improved in the three hour's exposure of the mirror to the night air. It lives in unheated accommodation anyway so its thermal differentials should be quite small. I have not yet tried the 12V cooling fan which I fitted to the mirror cell. There seemed to be little or no thermal agitation of the image this time. Previous observing sessions were plagued by tremors.

The orange, near full moon was just climbing above the horizon as I packed everything away again. It would be hours before it rose over the hedge. If at all. Everything was now saturated with dew.

As mentioned above, I have bought a few more secondhand eyepieces and a cheap plastic case to match the longer focus of the 10". With powers being 2/3rds greater compared with the 6" F:8 I had no useful range of magnifications except for the dirt cheap lenses which came with a £70 70mm Bresser refractor from Lidl.

I have Dymo labelled the case lid to make finding the correct lenses easier. The Meade text is impossible to read without donning reading glasses and using a bright torch. No doubt I shall eventually remember the magnifications available from each eyepiece. Note how the carrying handle is moulded in both base and lid. So the contents are never likely to spill out while being carried. Not even if I forget to close the snap locks. Some of the small, alloy storage "suitcases" are very vulnerable to popping open.

I really need to obtain a laser collimator to sort out the alignment more quickly and positively. I may yet fit a four vane spider to overcome the weaknesses of the curved spider. I may also fit a square section tube to the OTA to provide an extra degree of rigidity and somewhere to mount a finder. A slow motion focuser would help too. The short range of good focus was a complete surprise after using refractors for so long. The 10" is either in focus or not. There is really no leeway despite it being a long focus F:8.

I also intend to make a simple, plywood, counterbalanced, offset fork mount for the 6" refractor with Dobsonian bearings. I need a reference to compare the seeing through the 10". The fork can sit on top of the heavy steel pier to provide visual comparisons with the 10".

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MkIV slow motions.

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I spent an hour refitting the slow motions to the MkIV mounting. On the advice of a contact I tried to adjust the worm backlash. Removing the motors was easy enough once the protective cans have been wriggled out of their snug castings on the ends of the worm shafts. A tiny grub screw pinched against a flat on each motor shaft. So this should be backed off slightly to allow the motors to be drawn out of the sockets in the ends of the worms. The two long, motor-gearbox holding screws could then be slacked off and each motor-gearbox assembly carefully withdrawn by wriggling them carefully.

In an ideal world one would have a spare length of motor sized shaft with a flat filed or ground on it. This could then be inserted into the now empty sockets in the worms. The backlash, friction and freedom could then be easily sensed while twiddling this length of imitation motor shaft back and forth in the fingers.

There is no point in reducing backlash if it means over-tightening the big fixing bolts on the worm housings until the worms will no longer turn freely. I used a cross-head screwdriver as a tool to turn the worm back and forth because it just happened to fit the hole well enough to allow me to turn the worms easily.

The worms should be square to the wormwheels and at the correct height to bed perfectly in the curve formed by the cut "teeth" on the rims of the wheels. On my own worm housings are two socket head grub screws to adjust the height and tilt of the worm housings. The odd thing is that these screws are on the opposite side of the fixing bolts. So tightening the grub screws increases the pressure of the worm on the wormwheel. Which seems counter to common sense.

After fiddling with the worm housings and the tightness of the fixing bolts I greased the worms and let the motors run to ensure the worms were actually rotating. The worms turn very slowly indeed so one has to watch marks on the worms very carefully to see if they move. It can take a couple of minutes before the engraved setting circles move past the pointers to confirm wormwheel rotation.

As is usual with any mounting the balance is crucial to ensure freedom of movement when driven. If the motor has to work hard to lift the OTA "uphill" then drive accuracy is unlikely. The same could be said it the telescope wants to run away downhill because it is too heavy for the counterweight. The drives should be freed and the OTA (telescope) adjusted for longitudinal (see-saw) balance around the declination shaft.

The counterweights must also be adjusted along the declination shaft to ensure the entire mounting is in balance with the telescope around the polar axis pivot. Some telescope tubes are fitted with sliding, or threaded weights to adjust the telescope tube balance end to end. Changing accessories at the eyepiece can easily alter the tube's own balance. Particularly if a heavy camera is fitted in place of a simple eyepiece. It will also alter the balance around the polar axis unless care is taken in fitting a sliding tube balance weight to compensate.



The images in this post are all from the first arrival of my MkIV. Conditions aren't conducive to technical photography at the moment. With heavy overcast skies and short daylight hours.

Click on any image for an enlargement.

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12" Fullerscopes reflector OTA on Astrobuysell(UK) & a 6" F:8 on eBay UK

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http://www.astrobuysell.com/uk/propview.php?view=76694

A 6" F:8 on a MkIII

ebay.co.uk/Fullerscopes 6" F:8

10" f/8 Still, clear, Moon with Jupiter rising.

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For the first time in what seems several months the sky is clear without a howling gale. I dragged the MkIV mounting to where I could catch the rising Moon over the 20' eastern hedge.

I had found and tried the Cheshire and discovered the focussing mount was not square to the secondary. I slipped a galvanised nut under one edge and re-tightened the screws. That's better!

The Moon was at 25 degrees altitude when I first started observing. Creeping up to 35 degrees before I went in for a cup of tea and a slice of Christmas cake to scribble some notes on my blog.

Jupiter is still too low to align the telescope on it but is rising quickly now. Though it is still at a very low altitude.

Initial impressions on the moon at 100x and 135x is much increased sharpness. 200x was much too soft until the Moon reached 40 degrees altitude.

High frequency thermal effects are causing a constant rippling of the image. Stars are slightly elongated and not very small. I don't believe the optics are pinched. Infra and extra focal expanded images are round but jagged edged.

Going back out now:

By about 7pm the moon reached 40 degrees altitude and suddenly the central crater popped out as a small white spot. at 135x. (15mm)  I was still unable to see the crater at 100x. Thermal agitation gradually reduced with increasing altitude.

One oddity was a complete reversal of the light breeze. A thin streak of smoke was wafting horizontally from our chimney lit by the bright moonlight. Though this wind was undetectable where I was standing

Meanwhile Jupiter became accessible from my observing position though it was still only at 20 degrees altitude. Two clear belts visible but struggling for finer detail. I spent another hour going up and down in power until it reached 30 degrees. There was some slight increase in contrast on the belts but nothing very impressive. The four Jovian moons were easily seen and slowly shrank in size with altitude gained. At higher powers it was easy to see rotating thermal effects on the Jovian limb.

Soon everything was sparkling with frost though I was not suffering from any dewing on the optics. The earlier, heavy plates of cloud had disappeared. To be replaced but a long streak of thin,  high cloud appearing from the NW. It looked rather like a diffuse searchlight beam. For some peculiar reason this "cloud" formed a perfectly clear circle around the moon and then travelled under it and onwards.

Towards the end I brought out the short zoom, Canon compact camera to take some handheld snaps at the eyepiece. I seem to have mislaid my favourite 20mm no-name Plossl photography eyepiece. This fits the adaptor I made out of a plastic bottle top. The combination provides perfect centring and a reasonable power on my refractors. Though 20mm may be too "powerful" for the F:8 10".

The moon image was taken with a 26mm Meade 4000 Plossl. ( Nominal 78x) Cropped to enlarge and resized smaller for the blog.

Four hours in total under rather pleasant observing conditions. I packed up at 8pm for dinner with more, thin high cloud arriving. Both my quarries were both still too low for best seeing. Thermal agitation was a constant feature.

Telescope collimation is still not perfect but sneaking towards it. There is some vibration when I touch the telescope but it soon damps down. Having the drives fitted would remove the need to more the telescope by hand.  Though I have yet to re-attach the worms and slow motion drives to the MkIV mounting. The mirror fan has yet to be connected to a power supply even experimentally. Blackening in the optical path only amounts to an A4 piece of thin, black foam attached with clothes pegs opposite the focuser.

Clear nights have been exceptionally rare this year. Rather dimming my enthusiasm for further telescope building or observing. I remain determined to find a raised yet sheltered site which will allow permanent set-up for observing. Almost anything would be an improvement  on having to move the entire instrument and its separate mounting around the garden. The mature trees and high hedges provide shelter from the constant winds but block most of the sky.

I used a laser rangefinder, with an accurate digital clinometer, to measure the altitude of the telescope tube as the evening progressed. This made my own estimates of altitude (by eye) look rather foolish. I was being far too optimistic by as much as 10 degrees. Over the years I have usually noticed a distinct improvement in seeing when an object was above 45 degrees altitude.

Click on any image for an enlargement.

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