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Thank you for replies.
I should have probably explained that I "played" with the mirrors and changed the spacing so it is not correct now. I needed to know the correct value so I can set it with the help of plate solving.
(I have also emailed the question to GSO but no reply yet...)
Marc, the aperture at the very front is 220mm but I think the size of the primary mirror is the important factor for the focal length (200mm*f8 or 203mm*f8).
Marcus, when you said that the scope is spec'd to 1600mm, have you got a confirmed source that it is 1600mm and not 1623mm?
To answer your other question, the adjustment of the distance between the primary and secondary (which affects the final focal length as measured by plate solving) is achieved by shifting the secondary mirror (there is a screw in the middle of the primary to shift it in/out).
David, did it plate solve to 1628mm when the scope was new? I have found an old image when my RC8 was relatively new and it was 1610mm. Not very conclusive as it is in the middle between 1600 and 1623.
Thank you again for replies.
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