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AE 12" Newt/Cass telescope -Mirror separation

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Americo Watkins's picture
Last seen: 2 weeks 2 hours ago
Joined: 11/03/2014 - 13:12
AE 12" Newt/Cass telescope -Mirror separation

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.

Best wishes,

Americo Watkins's picture
Last seen: 2 weeks 2 hours ago
Joined: 11/03/2014 - 13:12
Mirror separation solved


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.



Jeremy's picture
Last seen: 11 min 1 sec ago
Joined: 04/03/2014 - 22:00

Sounds a really interesting and worthwhile project, Eric. I hope you'll document it and share how you get on with members.

Good luck!