A little while ago I purchased an AE 12″ F:5/20 Cassegrain telescope with an 3″ diameter secondary mirror which I plan to use for lunar and planetary imaging.
The owner sold it in the Newtonian mode and had forgotten the primary-secondary optimum mirror separation for this particular telescope. I plan to renovate the OTA by using carbon fiber tubes to replace the original 6 aluminum tubes that form the skeleton OTA. Also I will add a modern focuser. Does any member still have a similar telescope or can recall the mirror separations?
I have contacted Martin Mobberley who once had a 14″ similar telescope. However, the separation came already set upon delivery and needed no additional thought. As Martin suggested I could plate solve images to determine the plate scale making any necessary adjustments until I obtain the expected F:20 focal length.
Hopefully, any owners past or present may already have the information to give me a head start.
with further assistance from Martin and ES Reid ( maker of mirrors for AE) together with using the Cassegrain equations and comparing to the existing Newtonian set up the problem has been resolved. Answer being 45″ with a little tweaking when compared to images if necessary.
Thanks if you took some time to give this your attention.