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RE: [OM] Auto Exposure Times & The Ideal Meteor Catcher

Subject: RE: [OM] Auto Exposure Times & The Ideal Meteor Catcher
From: Wayne Harridge <Wayne.Harridge@xxxxxxxxxxx>
Date: Tue, 23 Mar 1999 22:31:32 +1100
David wrote:

> It's really based on measured EV rating, I think, rather than time. So
> you'll get longer exposures with slower film, at least within some
> limits, and of course, this doesn't take into account reciprocity
> failure. Here's the specs I have:
> 
>       OM-2     60sec @ ASA100 (approx -5 EV)
>       OM-2n   120sec @ ASA100 (approx -6 EV)
>       OM-2sp  120sec @ ASA100 (approx -6 EV)
>       OM-4    240sec @ ASA100 (approx -7 EV)
>       OM-4Ti  240sec @ ASA100 (approx -7 EV)

I did some tests with my OM-2n and got the following results using a body
cap (ie. no light):

ISO 100         3 Min 48 Sec
ISO 1600                3 Min 44 Sec
ISO 25          3 Min 48 Sec

The thing to keep in mind is that even though it gives you a long exposure
there is no guarantee of the accuracy.  My guess is that with very low light
levels, leakage currents within the exposure/timing circuit probably have a
major contribution in determining the actual length of the exposure.
Perhaps the "spec" is the longest exposure for which the exposure/timing
circuits are reasonably accurate.

> 
> None of the amature series OMs need apply (they're around around 0EV,
> maybe 2sec at ASA100).

I got the following results with my OM-10

ISO 100         8 Sec
ISO 1600                <2 Sec
ISO 25          26 Sec


Wayne Harridge
Ivanhoe, Victoria, Australia
http://www.geocities.com/Paris/Louvre/6152/ 

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