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Re: [OM] - Brighter screens and meter readings (reprise)

Subject: Re: [OM] - Brighter screens and meter readings (reprise)
From: "Roger D. Key" <rdk@xxxxxxxxxx>
Date: Wed, 2 Oct 2002 14:07:54 +0200
The OM-2SP and OM-4Ti measure light through the same two SBC sensors in the
light box during both viewing and the taking of a photograph. When viewing,
light is measured through a semi-silvered section of the main mirror, via
an additional mirror that hangs down from the back of the main mirror. The
semi-silvered main mirror is the cause of some loss of light in the
viewfinder (about 15% ?), which is compensated for by using the 2-13 or 2-4
viewing screens.

Note that this system of light measurement throught the semi-silvered
mirror requires the use of a circular polarizer filter instead of a linear
polarizer filter, to measure exposures correctly in manual mode.

Roger Key




Thanks, Ralf / Roger!

> OM-F/G and OM-40 have a fixed focussing screen.

I do apologize for my superficiality! :( I perfectly knew that!!!

> OM-4Ti does all light measuring in the camera's light box,
> so the focussing screen has no effect on light
> measurement.

The point was just this, for what I knew (I do admit my ignorance!), I
thought that the OM-4Ti / 2SP light measurements, when not in manual / spot
mode, were done with a similar pair of cds cells in the pentaprism as the
OM1/2 do...

Do you have any URL to suggest, for me to know how the OM-2SP/4-Ti auto
metering mode does precisely work (and I don't mean the OTF direct light
measurement, but the exposure time estimate)? It's just for curiosity's
sake...

Thanks again!

Fabio







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