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Re: [OM] focussing aid/screen Q

Subject: Re: [OM] focussing aid/screen Q
From: "Hans van Veluwen" <mail@xxxxxxxxxxxxxxxx>
Date: Wed, 1 Dec 1999 18:25:55 +0100
Brian wrote:

: This is equivalent to a matte screen with clear centre spot. Olympus don't
: make one of these, but now you know how to make your own :-)

There is of course the 1-11, matte with a cross-hairs centre.

: The thing that I don't understand is this:
: Olympus makes focussing screens (1-5, 1-6, 1-7, 1-12) that have *no* matte
: portion, i.e. there should only be an aerial image. How come you don't
: see the edge of the rear element, as you would with *no* screen installed
: in the camera?
: Is this due to the rest of the viewfinder optics? Is there a fresnel
: component to these screens?

Yes. As a matter of fact, the matte screens also have a fresnel surface, outside
the centre. This is why the centre of the 1-4 screen is brighter than the rest 
of
the surface. The structure of the matte in the centre looks identical.

: If so, are the fresnel rings visible through the viewfinder?

Yes, but they are very fine. They are easiest to see when you remove the lens.

: Answers (or comments/criticisms) on a postcard, please.

Merry Christmas and a happy new millennium.


H@nz


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