9.06.19 Adding the 90mm Vixen to the mounting.

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Sunday 9th. A bright but rather cloudy day with a dying wind. Added the 90mm Vixen f/11 refractor to the tube rings of the 6".  The little Vixen makes an ideal quick look instrument and a better finder. Nice and sharp with a wider field of view than the 7".

I fitted a 90° star diagonal and my existing home made Baader foil solar filter to the 90mm. Sadly there was nothing to see on the sun in white light today.

First I spent some time rebalancing the telescopes on the mounting. Mostly this involved moving the existing offset weights. They just needed to be extended further from the cradle. Only oddly arranged instrument should need such weights. A single OTA should be balanced with a simple counterweight. Offsetting OTAs relative to the main instrument will usually demand offset weights to compensate.

I decided that it made absolutely no sense to mount the 90mm on the 6". So I removed the offset weights and the tube balance weight's on their slide rail. Then moved the 90mm to the side of the saddle opposite the 6". The 90mm refractor is very much lighter than the 6". So the radial [offset] balance is still wrong despite the single offset weight I added to one of the 90mm's tube rings.

Ideally it needs tall pillars to increase the lateral offset of the 90mm from the cradle without adding extra weight. It's a dreadful picture, I'm afraid, because I can't get far enough away. I can probably take a better overall picture through the observation slit.

Thanks to the removal of all the small balance weights I was able to reduce the main counterweight by one disk to only 15kg. All it took was a short spacer to move the three weights further away from the mounting. This ploy could be extended by moving the main weights even further towards the end of the newly lengthened Dec shaft.

I am still struggling with backlash at the worm of the RA drive. I'm just going to have to use spring pressure. If I remove the backlash, by moving the worm closer to the wormwheel, then the drive motor just keeps stalling every few seconds. Spring loading would allow for concentricity errors.

I laid a long bar across the drive housing on the mounting to check it wasn't distortion causing this backlash. The support bracketry/motor housing does flex very slightly when I rock the declination shaft outboard of the counterweights for leverage. The the movement is almost invisible to the naked eye on the end of the long bar I used to magnify any flexure by leverage. The lever could be no longer than the radius of the dome so about 1500mm to 150mm or [say] 10x magnification at the tip.

With luck the balance should be good enough to have a quick look at the Moon in the 7" albeit in daylight. At 55N it never really gets fully dark in June. I enjoyed a low contrast view before gorgeous, wave and brushed clouds came over. The binoviewers with a pair of 26mms and WO GPC/Barlow for about 170x helped to darken the sky. All looking very crisp.

The big FeatherTouch focuser and 100mm x 2" extension, with triple thumbscrews fitted, is as solid as a rock! I can have the binoviewers horizontal, if I like. They just sit there without wanting to rotate downwards. This was completely impossible with the Vixen 2" focuser. It was a case of balancing the binoviewer as upright as possible and praying it would stay in place. It all felt so utterly amateur. Making binoviewer use a "dangerous sport."

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