To: atm{at}shore.net
From: "Matthew L. Brown" 
Reply-To: "Matthew L. Brown" 


Short focal length means:
1. shorter tube (which generally means stiffer, lighter, and easier to
transport, etc.)
2. lower magnifications for the same eyepiece 3. more of a challenge for
eyepieces to keep fields flat, etc. 4. more sensitive to misalignment
5. more of a challenge to figure
6. larger diagonal, so a bit more obstruction


Especially for larger diameters, it means a tube that can fit in your car
without major disassembly
The eyepiece is lower to the ground (no ladder for big diameter newts). You
don't need a long room to do foucault testing (which is done at twice the
focal length)

I'm making a shorter focal length 4.25" for a nephew -- the tube is
more convenient for a kid and it's easier for me to make it rugged.

Of course, clever people have figured out ways to ameliorate longer focal
lengths (easily disassembleable mechanics, tertiary mirrors,  levitation).

=Matt



>Newbie Alert!
>
>Does a short focal length have any advantages beyond making the scope
>shorter?
>
>Steve Houlihan
>Santa Cruz, California
>
>sho{at}starband.net
>http://sho.mystarband.net/
>http://www.surfnetusa.com/sho

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