I don't have my Shipman book handy, but I believe that the OM-2n photocells
(located on either side of the eyepiece, I think) measure the light falling
on the screen, so any change in the intensity of the image on the screen
will result in an exposure error. The OM-4 (and its later versions, as
well as the -2S) measure the light that falls through a half-silvered main
mirror , and then is reflected to the photocells in the floor of the mirror
box by a secondary mirror behind the main mirror.
Therefore, the type of screen used has no affect in the -4 (and -2S and, I
believe, the -3 as well) because they all measure light in the same way
(before the screen), whereas the -1 and -2 (including "n" variants) will be
affected by the type of screen used.
I guess that it's possible to measure the difference in the 2-4
screen-equipped-OM-2's meter reading against a Known Good Light Meter (we
all have one of those laying around, right??) off of, say, a gray card, and
dial in an appropriate ISO compensation. Has anyone tried this?
See ya.
Mahlon
------------------------------
denton @ asan.com (Denton Taylor) (Mailed by: denton @ asan.com (Denton
Taylor) @ internet)
06/16/98 07:16 PM EDT
To: olympus@xxxxxxxxxxxxxxx @ internet
cc: (bcc: Mahlon R. Haunschild)
Subject: Re: [OM] Beattie focus screens on 2N
>>I picked up a Beattie screen for my 2N, based on the salesperson's
opinion that it would have only a minor effect on my metering. When I got
it home and did some testing, I found out that our conception's of the term
"minor" varies somewhat-the meter was underexposing by a full 2 stops. >>
Strange. I used it on my OM4 with no discernable difference. MAybe the 2n
and 4 meter differently...
Regards,
Denton Taylor
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