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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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