Have any of you tried to install this focuser on your Onesky? Or would you recommend a different focuser? Thanks!
I'd recommend you try a very simple modification to the existing focuser before getting involved in a replacement. It has worked wonders for me. All that's needed is to replace the thumbscrews, as shown in the photo below.
The idea of using a longer thumbscrew, or attaching some other long lever to the focuser, is an old one, and if you look through the posts on this topic, you'll probably find multiple examples. But perhaps not everyone realizes what a difference this can make.
Obviously, one way it helps is by "gearing down" the mechanism. It's why people add peanut-butter-jar lids to the knobs on some rack-and-pinion focusers.
But that's only part of the story. The long arm also acts as a lever, reducing the force needed to turn the focuser's drawtube. Any force applied in focusing by hand not only turns the drawtube, it also slightly moves the scope as a whole, resulting in image shift and vibration--things that make focusing more difficult. Reducing that force can make an enormous difference--much more than you might expect.
You can find thumbscrews like the ones I'm using by searching eBay for "nylon thumbscrew m4." I like the white ones because they're easier to see in the dark, but I see only black ones available on eBay these days. I chose a 30mm length--that's the threaded part only. (I cut one thumbscrew shorter with a razor blade because that helps with packing the scope into the case I'm using.) The end of the 30mm thumbscrew easily clears the red-dot finder, as you can see.
These particular thumbscrews have certain additional advantages. First, nylon doesn't scratch an eyepiece barrel the way metal does. Second--an unexpected bonus--the tabular end allows me easily to keep track of the number turns of the screw. I quickly learned how many turns it takes to avoid snagging the undercut on an eyepiece barrel.
When I first added the longer thumbscrew and focused with one finger lightly on the end it, I was amazed by how much it helped. I found I could focus much more quickly and with greater precision. Whether it would help you as much may depend on other details of your setup. The only other alteration I made to my focuser was a light application of chapstick to the threads, just to cure a slight roughness in the movement. If you've added heavy grease or if you're squeezing your focuser with a hose clamp you may have increased the force needed to turn the focuser, so you may have more vibration than I, even with the longer thumbscrew. Also, if you have a rock-solid mount you may not have much vibration anyway when you focus.
It's easy enough to try.
Edited by Lazaroff, 07 March 2021 - 03:46 PM.