Archived posting to the Leica Users Group, 2002/03/06

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Subject: Re: [Leica] Optical Question
From: Henning Wulff <henningw@archiphoto.com>
Date: Wed, 6 Mar 2002 14:07:48 -0800
References: <MBBBJHIBKCKEAEOKKBPOCEIJCMAA.bdcolen@earthlink.net>

At 1:17 PM -0500 3/6/02, B. D. Colen wrote:
>Okay, all you Optigods, a question for you:
>
>If a + diopter is a magnifier, wouldn't a +1.25 diopter do the same thing
>that the new $229 Leica M 1.25 Viefinder magnifier does - for $73, without
>protruding from the back of the camera, and without the really cute little
>chain and carrying case?
>
>I am, of course, being a bit facetious - but the question is absolutely
>serious. If they aren't the same thing, what is different about them in
>terms of function?
>
>Thanks

A + diopter may be termed a 'magnifier', but is is usually only a 
simple positive lens (Elpros and some other 'close-up lenses' have a 
weak negative element glued onto the strong positive element to 
correct chromatic aberrations). This changes the focal length of the 
optical system, making it shorter, so that at the same extension from 
the imaging plane it will focus on closer objects. In a camera 
eyepiece, it will correct the image so that the person looking 
through the viewfinder, whose eyes normally focus beyond infinity, 
can now see clearly in the normal range. Camera viewfinder images are 
usually projected at a distance of 1-2m. The important point here is 
that it changes the distance at which the viewfinder image is 
projected.

The 1.25 viewfinder magnifier is a small optical system which acts 
like a tele-converter, also known as a Barlow lens. This also changes 
the focal length of the system, but it allows the eyes to focus at 
the same distance to see the image through the viewfinder.

- -- 
    *            Henning J. Wulff
   /|\      Wulff Photography & Design
  /###\   mailto:henningw@archiphoto.com
  |[ ]|     http://www.archiphoto.com
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Replies: Reply from Greg Locke <locke@straylight.ca> ([Leica] custom frame lines)
In reply to: Message from "B. D. Colen" <bdcolen@earthlink.net> ([Leica] Optical Question)