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Re: [OM] Shutter + Exposure Test equipment limitations

Subject: Re: [OM] Shutter + Exposure Test equipment limitations
From: Mark Marr-Lyon <markml@xxxxxxx>
Date: Tue, 6 Feb 2001 18:28:38 -0800
Gary Reese <pcacala@xxxxxxxxxxxxx> wrote:
>This brings up an interesting, potential limitation of shutter and
>exposure checkers. All test equipment is not created equal. When testing
>a camera with a separate photocell for the viewfinder meter (like an
>OM-2), the readout in the viewfinder isn't necessarily what the camera
>is exposing at. You might have an accurate viewfinder reading, but be
>getting a wrong exposure, since that is controlled by a different
>photocell or photocells.
>
>Cameras with OTF metering would be especially prone to errors on older
>testing equipment without film plane sensors. Even equipment with a film
>plane sensor would have to have the surface of the sensor with the same
>reflectance (120r 18%?) as the curtains of the shutter.
>
>I'd love to hear some comments about this. Have equipment manufacturers
>accounted for this potential error in sensor reflectance? My casual
>observation says no.

I was going to compensate for this on my homemade shutter speed tester by 
gluing a piece of old film over my sensor holder.  My sensor holder is a 
block of aluminum with two photodiodes mounted in two holes, and it is 
held to the film rails with rubber bands.  The two small holes cut in the 
film for the sensors should have negligible effect on the film 
reflectance.  I have yet to try this out though, since I've only used it 
in manual mode.  In its present form, it is only a shutter speed tester, 
and not an exposure tester, so I would only be able to tell if the OTF 
shutter speed was the same as the viewfinder shutter speed anyway.

Mark Marr-Lyon

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