Returning after a long absence.
A few years ago I managed to obtain a 12" F5/20 classical Cassegrain/Newtonian OTA and mounting. I wish to use the Cassegrain configuration mainly for lunar and planetary imaging.
Unfortunately the previous owner left the telescope in the Newtonian configuration and hence unable to determine the Cassegrain inter mirror spacing. I'm looking through the various formula and software to try and determine the best mirror separation. I hope to test out the set up in it's original OTA and if results are satisfactory I would like then to make a new carbon fiber truss OTA for it.
If I set out some of the measurements I'm hoping someone would have the skill and knowledge to determine the best spacing's for planetary imaging.
Primary focal length, 60 "
Aperture secondary mirror 3"
Primary focal length 60"
Secondary amplification x 4
Effective focal length 240"
Secondary mirror radius of curvature 20". Secondary freshly aluminized and clear flat back so reversed mirror and measured CR approximately to be 19.5", but with refraction through the thickness of the class I reckon 20" would be correct and will specify that.
Primary mirror thickness. 1.5"
Primary centre hole diameter 2.25"
Existing Primary mirror cell gives a distance of mirror thickness + cell = 1.5" + 2" = 3.5" to which the length of focuser needs adding which would be a moonlite with flange, i.e. 4.5".
So total is 8" Some allowance range for focusing in prime focus and Barlow/Powermate projections.
These are the measurements I'm working with. I don't think I will need a big field of view since I'm mainly imaging and planetary cameras have a small chip size so I was thinking min 8.5min/arc to 17 min/arc.
I'm new to this, but I'd like to have a good go at the project if anybody can come up with the required measurements I'd be extremely grateful and full acknowledgment given.
Best wishes stay safe,