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Re: [OM] Focal Reducer

Subject: Re: [OM] Focal Reducer
From: "Carlos J. Santisteban Salinas" <cjss@xxxxxxxxxxxxx>
Date: Mon, 2 Sep 2002 18:40:07 +0200
>Apparently the astronomical community is way ahead of us. They
>have such a thing already, called a"focal reducer".

Not quite... The focal reducer does give a brighter image, but it covers
less area of the film, so the field of view remains unchanged. Thru a
'scope, it's quite common to get severe vignetting with the reducer, but
since the picture is usually cropped, it doesn't matter.

>Wouldn't it be nice to put our 50/1.4 on the new ODSLR and get an f/0.5
>with a normal field of view? Or the 250/2 and get a 100/0.7?

I'm afraid these things aren't "universal", like teleconverters or Barlow
lenses (the astro version of a teleconverter); they are designed for an
specific focal length. There might be problems with flange-to-film (or CCD)
distance, also.

...

Carlos Santisteban

<cjss@xxxxxxxxxxxxx>
<cjsantis@xxxxxxxx>



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