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Ronchi Mirror Spacing
Posted: Tue Jul 05, 2022 9:06 pm
by DMouse
Hi, I am having some issues with my 12 inch RC, the images are a little fuzzy. I have ordered a Ronchi grating eyepiece as this will show if the mirror spacing is correct. I know I have the collimation spot on so its not that! The question is to adjust the mirror spacing is it best to change the primary or secondary spacing. The secondary would be simpler as the spacing is set by the center screw. The primary relies on adjusting all three push pull screws to move it.
Any thoughts or tips?
Thanks in advance
Paul
Re: Ronchi Mirror Spacing
Posted: Wed Jul 13, 2022 8:15 pm
by John Baars
I am not an owner of a
RC telescope.
As far as I know a
RC telescope is by far the most difficult telescope to collimate, due to the two hyperbolic mirrors in it. Articles I read about it confirm that collimation and sharp images are only possible when the exact calculated spacing is used. In this article the secondary is mentioned to achieve the correct spacing. Please read the following and follow the links:
http://www.ianmorison.com/experiences-w ... telescope/
Re: Ronchi Mirror Spacing
Posted: Sun Jul 17, 2022 2:34 pm
by DMouse
Thanks for the reply John. In have been using the Howie Glatter laser collimator for initial setup and then using my camera to do the DSI method. As for the spacing, my Ronchi eyepiece arrived yesterday and it did show some over correction. I adjusted the push-pull screws of the primary mirror and the lines straightened out, pretty cool. I then did a bunch of visual viewing before taking some images for testing. Of course now I have messed with the primary the collimation is off again, but at least I know I can get that back fairly easily. I guess after a couple of iterations both spacing and collimation will fall into place, very much looking forward to that.
I am reluctant to adjust the secondary for two reasons. One, is that getting the spacing way off from the original setting is a concern and Two is that the secondary can start to move away from the middle of the tube, we are only talking fractions of a millimeter here that can make a big difference.
I did buy the imaging version of the Ronchi eyepiece and plan to connect my planetary cam to it and take some pics and then write a tutorial on my website, job for a cloudy night, eh!!
Cheers
Paul