Help needed - finderscope conversion to guide scope project

[peter_4059]

Hi ATM'ers,

I'm embarking on a project to convert an old finderscope into a guidescope and need some advice. I am wondering how to determine the position of the guide camera imaging chip so I can make the required adaptor to attach the camera to the finderscope with the eyepiece removed? I plan to adjust focus by sliding the camera nosepiece in/out of the 1 1/4" tube.

This will be my first turning project after the recent aquisition of a lathe. I'm planning to turn the adaptor from some aluminium bar that I already have. Should be an interesting exercise to cut some threads also.

The reason I'm doing this is because I want to try mounting a guidescope directly on my Newt to see if this solves the flexure mystery, I need a project to justify purchasing a lathe and finally because I like to have a project!

Any suggestions gratefully received.

Peter

[M_Lewis]

Look at this site:

http://msfastro.net/articles/finder_guidescope/

I did something very similar with it on a spare finder scope I had kicking around, however instead of making a dedicated insert, I just got a 2" to 1.25" adapter, unscrewed the lens out of the finder scope, and turned down the adapter to fit, which from memory was just under 26 thou on the lathe. I made the fit so snug, it gave just enough resistance that with a slight tap of the hand on it, to make it secure. You won't actually need to do any thread cutting, nor will it affect the thread in the tube.

The beauty of doing it that way, was, at any time I could simply remove it, and screw back in the original lens. I found that the focus point was slightly different than described in that article, but the cmos chip from memory was well within the travel of the tube's limits.

I also found I didn't have to unscrew and remove the locking ring as described, rather, just screw that entire end (lens and locking ring) further onto the tube.

Hope that helps

Mark

PS: Having done all that - bought a ST80 2 weeks later....go figure. Not that it didn't work wonderfully, I found I wanted to use the finderscope visually for it's intended purpose. You could easily auto-guide from the above method though.