From: "Steve Houlihan" 
To: 
Reply-To: "Steve Houlihan" 


Thanks for all the replies.  One part of the answer is confusing.  Maybe I
should have asked "What are the optical advantages of short focal
length.

Bill wrote

>>The shorter focal length telescopes collects more light,

This must be why they are called "fast" but doesn't make sense to
me.  A mirror of a given diameter and reflectivity should collect the same
amount of light at any focal length.  Could someone please explain?

By the way, I am not planning on making a mirror at this time, but will
probably buy a 12.5 inch and build the rest.  At 12.5 inch and f/6 I can
still stand on the ground and get the scope into my SUV.  At f/4 it would
be a lot more compact and closer to the ground.  I guess I am asking about
the optical advantages between f/4 and f/6.

Steve Houlihan
Santa Cruz, California

sho{at}starband.net
http://sho.mystarband.net/
http://www.surfnetusa.com/sho

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