Jan@xxxxxxxxxxxxxx writes:
<< Well, the ultimate low-light OM is the OM-2 (without the "n"). By
that I mean "ultimate low-light," NOT necessarily "ultimate camera."
The OM-2 will do automatic exposures of an hour or more -- all other
OM models have a limit on this, to keep from exhausting your
batteries should the shutter go off in your camera bag. >>
Jan,
this has been discussed at length in the past by John H. and others. I
posted some qoutes from the service manual previously as there is a direct
comparison of the timing of the 2 versus 2n in the 2n service manual. My
memory was that maximum time is limited to 20min or less in the 2 (dependent
on ASA setting used.) Since times as long as an hour are often quoted by
users I checked the manual again. Sure enough it says in slightly stilted
English :
"After about 2 minutes (2 to 5 minutes) of the turning on of main switch ,
the LED lights up brighter than in the old type. As a result, there is no
posssibility of the maximum exposure time stretching out from 5 minutes and
up to 20 minutes."
This sounds pretty definitive the 2n is limited to 2 to 5min max and the 2 to
about 20min. The integration diagram for the old 2 also shows a label:
"maximum exposure time in AUTO (2 to 20min)". And the diagram for the 2n
shows 2min plus some several seconds.
However examining the diagrams more carefully shows that the conditions
the diagram illustrate only cover a range of ASA of 100 to 400. With 100ASA
showing the longest time. This means that at say ASA 25 the times would
probably get out to about 80minutes on the 2. So the hour time described by
users may well be "normal" at ASA 25 for the 2. ( If everything is just right
and the circuit board is not dirty.) Thus, it appears the "maximum" timing
spec for the cameras is at 100ASA only.
Another subtlety of the designs is that although the 2 can expose longer than
the 2n the exposure accuracy of the 2 is lower than the 2n for times up to
2minutes. This is because the LED limiter comes on near the begining of
exposure in the 2 but it comes on only after 2minutes or so in the 2n.This
means that long exposures in the 2 are systematically slightly underexposed.
In practise the reciprocity failure in the film probably makes this irrlevant.
Regards,
Tim Hughes
Hi100@xxxxxxx
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