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