Re: [ATM] My scope

["Eric S. Johansson" <esj@harvee.org>]

Mark Holm wrote:
> Eric S. Johansson wrote:
> 
>> but central obstruction is.  good planetary scopes have a tiny or no 
>> central obstruction (5-10% vrs 30%+ for a DSS).  tiny central obstructions
>> that match the light path means high f-number.
> 
> Yes, but remember that Gerald is making a first scope.  For at least a time,
> it will be his only scope.  The first one probably shouldn't be specialized
> to an extreme for one type of observing.

was just trying to get a perspective for him to decide.  Personally, I think the
classic f8 scope is a real good place for the beginner.  Not too hard to make
parabolic but will also work if you leave it a sphere.  Also, I suspect he will
shoot for F8, but end up with a f-6 by the time he starts polishing.  so maybe
he should shoot for an F12 :-)

> A Cassegrain is at least an order of magnitude more difficult to make. Lets
> help Gerald get his first scope made before we start filling his head with
> dreams of hyperbolic astrographs.

true.  Very true.  Although I've noticed that a lot of ATMs start out the
description of would ever scope they're currently working on as "the scope I'm 
going to build after this one is..."

---eric

-- 
Speech-recognition in use.  It makes mistakes, I correct some.
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