Re: [ATM] Re:(ATM) F/10 or F/8?

[Mike Lockwood <melockwo@uiuc.edu>]

Curtis,

Looks like there are not TWO Richards on the list that like to make 
humorous posts.  Keep them coming guys!

Anyway, I have two thoughts.

First, consider the longest length of the tube that you're willing to 
set up and transport.  That will determine the highest focal ratio 
that you can go with.

Second, if you're working without assistance from another experienced 
mirror maker, a 6" F/10 or F/12 spherical mirror will perform well and 
won't be too hard to make.  (If it's smooth, it will provide better 
images than you think.)  If things go well, you can always spend a few 
minutes parabolizing and get fairly close.  If you can get instruction 
from someone, then F/8 or less will be easier to handle, especially 
interpreting the Foucault shadows and taking zonal readings.  You 
don't have to take readings if you're just testing a sphere.

Just remember that many people have made their first mirrors with no 
help from others, and have turned out good parabolas.  It is quite doable.

	Mike Lockwood


Richard wrote:
> Hi Curtis,
> 
> Tuesday, June 14, 2005, 4:50:54 PM, you wrote:
> 
> CS> So, would it be better to go all the way to say a F/12 and leave it
> CS> spherical for simplicities sake?  Or would image quality suffer?
> CS> Remember this will mainly be a planetary scope.
> 
> Do you have experienced mirror makers at a local club that can
> guide you Curtis?. If you don't, I would go somwewhere around
> F/7 and get a good Barlow as someone else suggested. If you do
> have accessable help, then I'd go straight into a Cassegrain of
> some kind, preferably a Ritchey Cretien of 10" or 12". Your
> helpers would I'm sure enjoy the challenge. You could then maybe
> make a 6" F/5 first as your spotter scope :). But that's just me
> :)
> 


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