Guy's MkIII thrust bearing.

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Guy has fitted a thrust bearing to his MkIII. A very neat job it is too! 

Here is Guy's MkIII mounting after a tidy up and repaint. Note the screwed declination shaft. Suggesting a later model. As does the clarity of the Fullerscopes logo cast directly onto the polar axis castings and the pot base. Guy has fitted a longer pier pipe to raise the mounting for his refractor use. Originally this MlkIII held an 8" Fullerscopes reflector. The brass ring houses the ball, thrust bearing and protects it from the elements. The slow motion drives and motors, shown in an earlier post, have yet to be fitted in this image.

The polar axis is slightly withdrawn here to show the bearing assembly.

The thrust bearing with deep groove steel races and caged balls.

The brass bearing housing with the lower bearing slightly protruding to rest on the polar axis casting. Normally a MkIII would have a PTFE (Teflon) washer sandwiched between the castings to take thrust (end) loads. For lower friction with a heavier instrument the thrust bearing is a useful modification. The thrust bearing adds very little height to the polar axis so will not affect stability. The declination axis "T" rests on the upper brass face.  

The MkIII on its new, taller pier.



The "legs" are Fullerscopes Heavy Duty in cast iron. Offering greater stability  than the lighter, alloy model.

The MkIII stripped and ready for a repaint on its original, shorter, "reflector" pier.

The MkIII before restoration with its reflector.

 






An assortment of Fullerscopes parts and accessories. Including a threaded weight, finder/guide scope and VFO drive parts.






Click on any image for an enlargement.

Comments moderation

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I have finally discovered how to have comments notifications sent to me by email. Blogspot had made it so difficult that I had completely missed several comments made on older posts.

If anybody has not had a response to their comments feel free to have another try. I have set all comments to be moderated. I will then be notified automatically whenever comments are posted on any of my blogs.

New Dewshield:

The new plastic dewshield in place on the 6". It is 3 x aperture in length from the cell shoulder. Thanks to its light weight it does not make the tube any more nose heavy than it already was. It looks a bit long but this is due to the short length of the F:8 OTA. It slips over the original, metal dewshield. Which provides support and security. 

The material is not stiff enough, on its own, to stay in place with only a small overlap on the lip of the objective cell. Nor could the telescope stay safely parked "on its nose" without the tough, metal dewshield. So the plastic dewshield is removed after use and stored upright on a shelf. It keeps its cylindrical shape well and has a smart, lightly textured finish. I will have to make a long one for the Vixen now. It too has a rather short dewshield for optimum protection on dewy and frosty nights.

The CR150HD6 F:8 beside the Vixen 90M F:11 on the Fullerscopes MkIV.

I now stand on an old beer crate to reach the cradle more easily. The extra weight of the Vixen would otherwise be a bit of a struggle. When set horizontal the cradle is well above head height.  Probably 7' above the ground due to the tall but massive stand/pier. Thanks to the beneficial geometry the hinged, open rings accept the main tube and hold it safely without any risk of slipping out or falling. I lock the wormwheel clutches to fit and remove the OTA.

The pictures aren't great but it was a heavily overcast day and almost dusk. I shall take some better pictures when conditions allow.

The polar axis is far too long but I am still deciding whether to add a taper roller or axial thrust ball bearing races at the bottom. The  MkIV provides low friction with such light telescopes. Though friction does rise when large and heavy OTAs are fitted.

My idea was to add a screwed collar to the polar casting. Which would allow fine adjustment of end loads on the Polar Axis via a thrust bearing.You can't just add a collar and spring to the shaft itself. Or it would pull even harder on the thrust surfaces.

Some mountings have had a single steel ball taking thrust loads on the end of the polar axis. Because of the very small surface area of contact it reduces friction considerably. One still needs the thrust faces because they offer improved damping and stability over plain shafts.

I have removed a 10lb weight and replaced it with a larger one of 14lb. This compensates nicely for the extra weight of the Vixen. Releasing the wormwheel clutches and swinging the OTAs (gently) produces a similar momentum in both directions. By watching how soon the tubes stop in their rotation (in each direction) about the axes one can soon tell if a reasonable balance has been achieved.

Though not impossible, it is difficult to add the 90mm Vixen to the already mounted CR150HD. There is simply not enough room between the cradle and the tube of the 6" refractor. The Vixen's rings will not pass through this space without releasing the 6" tube from each ring in turn. Suitable packing pieces between the hinged rings of the 6" and the cradle would easily solve this problem. Being able to add the Vixen later would save lifting the pair of OTAs onto the MkIV together. 

I managed to find a couple of A3 sheets of the matt black, thin foam to kill internal reflections inside the new dewshield. I may reduce the length of the dewshield to 2.5x aperture. This would give a more balanced look to such a short F:8 instrument. Hopefully without compromising its shielding ability against dew and stray light.

I spent a couple of hours observing Jupiter again. Though beautifully clear at first plates of cloud kept crossing over. There was also a breeze which made my eyes water. Jupiter wasn't high enough to get a really sharp view. I left the scope out while I had dinner. Then found it fully clouded over when I went out again. To finish off the evening I fell headlong over the stand in the dark! Fortunately I wasn't carrying anything at the time. No ill effects.

Click on any image for an enlargement.

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November 15-11

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Dewshield:

I found a coiled tube of pre-curved, black, plastic sheet in a supermarket. Designed as a bin bag support for gardeners. It looked ideal for making an extension dewshield for the 6". Which has always suffered from objective dewing due to its ridiculously short dewshield length. The objective also projects well forward of the shoulder on which the dewshield is fitted. (by friction) Further increasing its exposure to dewing.

The plastic cut easily with scissors provided I held it flat with weights. It had a strong curling tendency. In fact it wanted to coil into a neat 4" diameter cylinder. Ideal for my purpose!

I slid the Celestron dewshield back into the middle of my new, smaller cylinder and taped the lengthways cut edges neatly on he outside with black gaffer tape. Then I removed the metal dewshield and taped the inside. I made the plastic cylinder 18" long overall. It now slides easily over the original dewshield but stays firmly in place.

I put the 6" onto the MkIV mounting and after several hours the lens was still dry. Though everything else was dripping wet with dew. So the dewshield extension is working as intended.

The inside of the plastic is a bit shiny but the dew matted it down. I intend to line the new dewshield  with thin, matt black foam from a toy/model shop. I'll post some pictures of the dewshield when it is light enough for photography.

Jupiter:

Having fitted the dewshield I spent the evening trying to take better images of Jupiter. I'd take a dozen images. Then go back indoors to see if I was making progress by viewing them in Picasa3. After each photo session I would take a snap of the monitor to separate the images into groups. Otherwise they all looked so similar it was hard to see where each sequence started and finished.

The TZ7 failed to capture a single image worth keeping. My old Sony DSCP71 produced something useful with almost every exposure!

As usual, I simply held the camera up to the eyepiece and centred it by touch. I took an exposure when there was a bright blob visible on the camera screen. 

The images which had potential were put through PhotoFiltre. I played endlessly with Gamma, Contrast, Dust Removal and Colour to bring out as much detail as possible. The four visible moons were captured but lost in the processing. 

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None of these is particularly good but satisfying enough considering the crude methods I used.  The Great Red Spot is just visible on the lower belt, left limb on my screen. I doubt it shows on the blog images. The third image shows it best. The Sony camera has captured all that I could see visually.

I tried a number of eyepieces and even the 2x Barlow and moved the Baader "Fringe Killer" filter across to each new option.

I tried all sorts of settings on the TZ7. Including spot metering and zoom but nothing helped show any belts. Though the moons were well captured as were a few background stars. The trend was always overexposure.

The evening session ended when the inside surface of the objective dewed up. The front surface was still dry. I had swung over to the rising Moon  to see if the seeing was any good that low. It was then that I discovered the misted lens surface. The telescopes are parked nose down so the 6" may have collected some fluff on the back surface. I'll have to take the objective cell off and clean the glass.

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November dew

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A first clear night for ages pushed me into having a look at a rapidly rising Jupiter in the East. The brilliant full Moon was hanging nearby slightly further to the north east. It was so bright I had no need of a torch when selecting eyepieces from my box.

I had to drag out the massive, welded stand supporting the MkIV. The wheels had sunk into the lawn since the last time I was observing. The pier legs are too big to allow the car to turn safely. So the whole thing has to be pushed out of the way each time I pack up for the night.



My original observing position became completely pointless as trees grew (and grew) around our garden. Ironically the view is clear all round in the drive just beyond the gate. But our neighbours are all afraid of the dark and need multiple bright lights on all night or they cannot sleep.

Somehow I had loosened the drive worm housings so the control paddle had no effect. The worm housings were moving around the wormwheels instead of the wormwheels being driven. I couldn't see this at first despite the bright moonlight. A 13mm spanner to the hex headed screw holding the housings soon solved that problem. The mounting then responded to the paddle controls.  

Full moon TZ7, 20mm no-name Plossl, 6" F:8 refractor. 
PhotoFiltre improved! Gamma reduction and contrast increase.

I was concentrating on Jupiter. Meanwhile everything was dripping wet with dew. Once, when I glanced through the telescope without the eyepiece and the objective was completely misted over! I broke with convention and mopped the front face with a clean handkerchief. 

I have a long, tubular, foam, slip-over dewshield extension but it was hiding somewhere in the shed. It is nothing fancy. Just a roll of black camping mattress and a rubber band. It works amazingly well compared with the stumpy, original, metal dewshield which came with the Celestron CR150HD.

 Jupiter proved far more difficult to capture. No visible markings even in the "best" of my hand-held, afocal snaps. I literally held the camera up to the eyepiece and snapped away every time I could see a bright blob on the camera screen. Two belts were clearly visible visually but I completely failed to capture them. I also lost a moon while reducing gamma in PhotoFiltre!  This is a heavily cropped shot with considerable gamma reduction to kill flare. Had I the patience I could have gone through the endless TZ7 menus and found spot metering. But I didn't. I had slightly more success with older digital cameras when photographing the planets in this crude way in the past.

 What I really need is a sleeve on the focussing mount to give the camera lens something to locate into. This would ensure centring on the eyepiece and also help with squaring-on.

I am always afraid to use a simple camera clamp to the focussing mount. Because the zoom lens might strike the eyepiece under power on camera switch-on. The lens seems to automatically extend for about an inch (25mm) each time the camera is switched on. This gives a fixed clamp no leeway to avoid direct camera lens to eyepiece contact.

These are my best images of Mars using simple hand-held, afocal methods.

A run through PhotoFiltre to enlarge, then adjust gamma and contrast has helped to bring out detail and reduce flare and false colour on the limb.

 Each image shows a different face of Mars.

A magnifying lens on the centre of the focussing screen would be useful for astronomy. I can't easily wear my reading glasses at the telescope just to enable me to monitor the camera screen. 

I don't own a laptop so can't try my webcam at the telescope. Without a camera clamp or lens, "nose socket" I can't take decent HD astro videos either.

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