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AT 8" RC Focuser Issues

Started by asimen, 09/12/2009 01:44PM
Posted 09/12/2009 01:44PM Opening Post
I appreciate all of the useful information that Floyd and others have
provided on Astromart regarding the AT 8” RC. I received mine about
one month ago and I am reasonably happy with it so far.

I am thinking about whether to replace the focuser with a Feathertouch
FTF2015BCR focuser. A lot has been written about problems with the stock
focuser but I have not seen any direct evidence that the focuser affects
performance of the scope. On the one hand, the focuser does clearly have
flexure. When I apply torque to the drawtube the focuser feels loose. In
comparison to the William Optics Megrez 72 that I use as a guidescope the
AT focuser is somewhat looser and flexes in a clunky fashion whereas the
WO focuser flexes in a smooth and progressive fashion with increasing
torque. My camera and filter wheel (QSI 540ws) are heavy enough (just
over three pounds) to induce a small degree of sag with the drawtube
extended to achieve focus. I am not sure how much this slight sag is
affecting my images.

This leaves me wondering how much flexure is too much and how rigid is
the Feathertouch focuser in comparison to the stock focuser?
Posted 09/12/2009 04:17PM | Edited 09/12/2009 04:17PM #1
Hi Arthur,
Well, any flexure is not good really. Even a little is like poor guiding, it leaves you will elongated stars.
The FeatherTouch is not a cheap option, but it is a good solution. The good thing is that the focuser can be used on more than one scope if needed. You just loosen the set screws and put it on another base.
I did not try to modify the original focuser. There is a possibility that you could do a little modification and make the focuser very solid. But what I have seen with the Chinese focuser is the bearings are too close together or something that allows the draw tube to pivot. But, if it is just a clearance problem, then a Teflon shim might fix that. If I did not want to buy the FeatherTouch then I would definitely take a close look at the stock one.
My camera and filter wheel are about the same weight and I knew that it would be too much for it. So, I figured on replacing the focuser when I bought the scope. If I sell it, I think the FeatherTouch will add value to the scope and if not, then I would just sell the FeatherTouch separately or keep it grin .

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 09/12/2009 04:27PM #2
Arthur Simen said:

This leaves me wondering how much flexure is too much and how rigid is
the Feathertouch focuser in comparison to the stock focuser?

How much is too much? Enough that stars are not sharp across the frame.

Uncle Rod

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