Re: [ATM] Flat grinding the back of the primary mirror

["Rod Brackenridge" <rjbr@lycos.com>]

Hi Terin,

As Mel said don't worry about grinding the back if you have a thick blank (1:6 ratio).  On your other questions, I think it's portability you need to consider.  If you can put an F10 tube in your car easily then that is what I'd make.  My first mirror was a 6 inch F10.  The advantage is that you can leave the mirror spherical so it is very easy to test - just look for straight ronchi bands or a clean null with the foucault test. For me this was a big advantage and gave me a usable mirror without too much trouble.

If you have young kids, the F8 is easier for them to have a look through and it's more portable. You have to do some parabolising but it's not hard (particularly if you know someone who has made some mirrors).  I don't think there's any optical advantage with the shorter focal length.

Hope that helps,

Rod Brackenridge
Mount Martha
AUSTRALIa

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