On Sat, 10 Jan 1998 21:00:33 -0600 (CST), Stephen wrote:
>Help!
>My OM2n seems to be overexposing. It started out that it was just
>on shots I took outdoors, and it was controllable by dialing in one
>stop or so of underexposure. But the last two rolls (slides) that
>came back vary from a bit overexposed to totally washed out, even
>the flash pictures. It's not just the flash overpowering a
>foreground subject, the whole frame is overexposed. The strange
>thing is that two or three of the shots on each roll look ok. Plus,
>I took a short roll of print film, and it seemed to come out ok. I
>guess they managed to resurrect it while printing. I guess my main
>question is whether this could be a problem with the camera, or
>whether it's a problem with that big lump behind it. Does the 2n
>suffer from oily magnets?
Possibly, but *don't jump to that conclusion*; I've been down this
road too!
Did this happen in automatic mode?
Try a roll using manual mode throughout, using the camera's own meter.
If that's perfect, it's *not* an oily magnet.
If that is so, the most likely cause is a dirty ASA resistor or its
associated wiper, which only affects the auto mode; there's nothing
wrong with the shutter itself. You can confirm this by trying another
roll, this time in auto mode; before each exposure turn the exposure
compensation dial back and forth several times to clean the resistor
(temporarily).
If all or most of your exposures are then OK then Hey Presto! The fact
that your flash pictures are very over exposed too makes this
conclusion almost certain. If it were an oily magnet that would not
happen, unless the shutter was held open so long that the ambient
light was predominant.
For info, the auto exposure "calculating" system of the 2n is
beautifully simple, elegant and very robust, electronically speaking.
It uses a comparator; on one side it gets a signal from the (inverse
of) film speed (via the ASA resistor) and the other side gets a signal
from the photo diodes that "look" at the film. The output from these
is integrated so that the voltage from that bit of the circuit rises
at a rate proportional to the light falling on the film. When this
voltage is the same as that coming from the ASA resistor side, the
comparator says "enough!", the shutter closes and the flash is
quenched. That's all there is to it. It's so simple that you could
probably make it with stuff from your Radio Shack (Tandy) store! If
the ASA resistor gets dirty, the comparator is fooled into thinking
that the film speed is much lower than it really is and so you get
gross over exposure from the shutter *and* flash.
In the 2n (but not the 2SP), the metering does not involve the ASA
resistor (in fact it's identical to the "springs and string" system of
the OM1) so *its* indication is correct.
In the 2SP, this fault can also occur but you tend to notice straight
away that something is wrong from the excessive exposure indicated by
the meter. I assume the same happens with the 4's?
AFAIK the cleaning is straightforward and nothing is likely to need
replacing.
Perhaps John Hermanson would comment?
Regards
--
John Gruffydd (Mold, Wales, UK)
##################################################################
# This message was delivered via the Olympus Mailing List
# To receive the Olympus Digest send mail to: listserv@xxxxxxxxxxxxxxx
# with subscribe olympus-digest in the message body.
#
# To unsubscribe from the current list send a message to
# listserv@xxxxxxxxxxxxxxx with unsubscribe olympus in the message body.
#
# For questions email: owner-olympus@xxxxxxxxxxxxxxx
##################################################################
|