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Moonlite focuser on EdgeHD 8" with reducer, OAG and EFW

MichaelLev
17 Jun, 2019 12:46
Hello astroneers!

I'm pretty sick of trying to autofocus with my celestron focuser, the mirror flop is just a major buzz kill.
I was wandering if it's possible to use a Moonlite focuser with the short back focus distance of the 0.7x reducer, a Celestron OAG AND a filter wheel.
I know that using it without the reducer is possible.
I'm using a ZWO 1600MM-Pro (6.5 mm back distance), ZWO filter wheel (20mm width), Celestron OAG (57mm with a shortening adapter, no use of the SCT adapter).
Without a Moonlite it totals at 83.5mm which leaves me 21.5mm.
I think that's longer than the Moonlite but i'm not positive.
Anybody know anything about this train? does anybody have a setup similar?

Thank for any help!
JoelShepherd
30 Jun, 2019 22:59
Short answer is a definite maybe. That’s basically how I set up my 8” Edge. Moonlite focuser with reducer nestled in, OAG, ZWO filter wheel and camera (Atik with 13mm back focus).

Now the caveats.  smile

It’s tight. Not much room for spacers and the travel distance on the focuser was maybe 1.5 cm. Took an unorthodox assembly sequence to get things to come together. Because the focuser throw is small, you center it, rough focus with the OTA’s focuser, lock the mirror, then fine focus with the Moonlite.

Second, my success with autofocus on that setup was spotty. I could speculate why, including my own lack of ability, and maybe the small pixel scale contributed. But TBH, the pictures I was happiest with were all hand-focused.

Even with hand focusing, though, the Moonlite was much easier to work with than the built in focuser.
gnomus
01 Jul, 2019 09:37
Hi Michael

I did try something similar - but it was a few years back.  I have mixed views about the Moonlite.  It is certainly an attractive piece of kit, and it works well for most applications.  I believe that you can even get a model that accomodates the reducer: https://www.rothervalleyoptics.co.uk/moonlite-chl-25-large-format-dual-speed-crayford-for-celestron-edgehd-8-telescopes.html (this is not the model I have though and so cannot comment on this particular version).

I had a lot of problems setting my Moonlite focuser ssuch that it wouldn't slip.  At that time I was using a Nikon D700 - I also tried it briefly with an Atik 383 plus Atik filter wheel.  Both of these were only moderately heavy - certainly not excessively so.  I found that I needed to keep a close eye on the focuser tensioner.  Indeed, I would spend some time adjusting the thing until I thought I had it set correctly, only to find that the next night it was slipping again.  Of course, the temperature changes from one night to the next - but whether that was a factor or not, I don't know.  And it is always possible, of course, that what I was experiencing was a result of user error.  The focuser works fine for visual or for lunar/planetary work.

My experience led me to decide that I would not use Crayford focusers for AP from that point forward.

The Baader Steeltrack focusers look interesting to me.  Because of their design they might have more initial 'inertia' against slippage - but I have had no experience of them whatsoever.  Perhaps those who have used these could chip in.

Final point (and I know I start to sound like a stuck record on this issue) - even with the 0.7 reducer the combination of the 8" Edge and ZWO 1600 has you imaging at 0.55" pp.  You're asking quite a lot of your mount at that scale.

Hope some of that is helpful.

Steve
 
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