Image of the day

From the
ATWB Customer Gallery

Great Horned Owl

My Account

New to Astromart?

Register an account...

Need Help?

Back Focus Distance Tips

Started by brucesdad13, 01/25/2015 09:49PM
Posted 01/25/2015 09:49PM | Edited 01/25/2015 09:50PM Opening Post
Me again... I'm reading up on imaging and all of the terminology and gear. I've sort of capitulated on my quest for a HyperStar alternative and am now wondering about back focus. My camera currently has a C-mount w/flange focal distance of 17.526mm (I think this is the universal standard for C-mount?). Starizona says HyperStar backfocus from mounting thread to focal plane is 39.8mm. Assuming I am able to find a used Hyperstar for my C8 and put the camera where the seconary mirror usually goes... what does the setup look like? Hyperstar (w/possible filter(s)) -> spacer -> C-mount? And then I focus by moving the primary mirror?

Confused as always... wink [image from Baader website attached]

Attached Image:

brucesdad13's attachment for post 59045

~ Charlie Stevenson

8" f/5.7 String Telescope - 1st Scope Build; 2nd Place Stellafane 2016 Optical Award for Newtonians 12.5" and Smaller
10" f/4.5 Newtonian (June 2015) mirror refigured by Optic Wave Labs P-V WaveFront 1/14.24, Strehl Ratio 0.993 (Aug '15)
Criterion RV-6 seems to be circa 1973 (June 2015) [For Sale]
Celestron C8-A XLT (January 2015) [For Sale]
Celestron PowerSeeker 70AZ (Christmas 2014)
Aldrich Astronomical Society member since 2015
http://astro.charleskelleystevenson.com/