I suppose a more scientific approach would be to place the camera on a
tripod, cover the eyepiece with black vinyl tape, and use the aperture
and ASA to set the meter so it's just below the top "overexposure",
i.e., so one more click on the ASA and the meter begins to beep. Then
remove the tape. Move the ASA one click at a time until the meter
doesn't beep when the tape is removed and you'll get an idea of the
gross possible deviation due to light entering the eyepiece. Of course,
there's lots of variables -- ambient light level, angle of acceptance,
etc. But if you've got nothing else to do on a bright sunny day.... ;^)
re: the OM-1, 1n, 2, 2n, 10, G, etc., the problem is that the meter
display is controlled by a CdS cell located by the eyepiece -- light
entering the eyepiece is reflected directly into the cell. This can
deflect the needle several stops in extreme cases! On the OTF models in
Auto mode, though, (and this goes for the 4/2s as well) the sensor that
actually controls the exposure in Auto/Program is below the mirror, so
light entering the eyepiece has virtually no effect.
DBellamy2k@xxxxxxx wrote:
>
> I have heard claims that there is no problem with the OM-4(T/Ti) etc. from
> stray light in the viewfinder, owing to the location of the metering cells in
> the baottom of the mirror compartment.
>
> Today I tried out my OM-2SP (sorry to bore you!) with most of my lenses, and
> I was walking back towards the house and it gave a little "beep!" - just one.
> I thought "Hmmmmm...". I had my back to the sun, so did the camera. I then
> deliberately pointed the camera so that the sun would hit the viewfinder. I
> got several more 'beeps' for "overexposure". Setting the lens to smallest
> iris aperture (f/16 or f/22 I can't remember) and re-trying, it didn't beep.
> Setting the aperture back to f/8 or a lower f-number, it beeped again.
>
> The OM-4Ti also beeped when the viewfinder was presented towards the sun. So
> thet is 1/2000 at f/8 worth of light getting to the silicon cells, EV 17.
> Presumably the light gets in through the pentaprism and past the
> semi-silvered mirror into the photo cell. Of course, it isn't all black down
> there because the shutter curtain might reflect a bit of this stray light to
> the cell, depending on the taking angle of the little dewdrop-shaped lens in
> front of it, or it might get to the lens on the photocell directly through
> the mirror and get refracted by the dewdrop lens into the cell.
>
> I used to suspect that this was possible, but I don't think I have ever
> encountered it before.
>
> Of course, this wouldn't be true for the OM-2 or OM-2n because of its fully
> silvered mirror! So correct exposures with the old OM-2(n) look a bit more
> secure in Auto mode.
>
> Dave Bellamy.
> http://hometown.aol.com/sitesearch/
>
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