Re: [APML] Prime focus advices for beginner

[Radu Corlan <rcorlan@pcnet.ro>]

On Thu, 11 Dec 2003, Eric Torraca wrote:

> Hello All,
> 
> Given that I have an F12.1 scope with a non-standard back, does anyone 
> have any links for plans for a home-made focal reducer? I've been 
> searching around with little luck.

You can try using an achromat pair. A ~300mm fl achromat (or maybe a
binocular objective?) placed about 100mm from the film plane will give you
a factor of 0.6-0.7 reduction. If the focal length is longer, or the
reducer lens is closer to the film plane, you will get less reduction. You
will have to make sure you have enough back-focus (the reducer 'eats'
quite a bit of back focus). You could try to push the lens up the baffle
tube if you want - it your scope allows this.

With a f/12 scope, i think you can get ok image quality with the above
settings, or any setting that gives you less reduction. When going for 
more reduction, you will need to have the reducer designed for your scope 
and film distance.

Radu

> 
> Eric
> 
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> 

-- 

-------------
Radu Corlan       Snail Mail: Bucuresti sect. 1, 
rcorlan@pcnet.ro  str. Argentina nr. 28, Romania

   You can still escape the "Gates" of Hell!   
                 Use Linux!                       


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