The MR9 adapter (from C.R.I.S.) is essentially the same solution you'd
get from John's permanent fix. The MR9 is a mercury battery size case
designed to take a smaller silver oxide battery. The adapter has a
diode built into the case to drop the voltage from the 1.55 of the
silver oxide to the 1.35 of the mercury.
John's permanent fix does essentially the same. He adds an O-ring type
spacer to the battery box to position the smaller silver battery and
then solders a diode in-line with the meter. My recollection is that
either solution will give you the same small metering errors at the
extremes of the meter's range. Tim Hughes has posted a much more
sophisticated solution to resolve the errors at the extremes but I don't
know if anyone has ever built it.
Wein cells are zinc air cells (same as hearing aid batteries) and are
nominally 1.4 volts instead of the desired 1.35 volts. That will
introduce a small metering error but I don't know how bad it is.
Probably not much. Last I knew Wein cells were about $5 which is a lot
more than hearing aid batteries. If you can't find a Wein cell locally
you might just run on down to the drug store (chemist's for you folks
across the pond) and see if you can find an appropriate size hearing aid
battery. They're pretty cheap and maybe worth a try although you'll
probably have to fit some sort of shim around to hold it in place. Check
the meter against another camera and if there's an error just compensate
with the ISO dial. Zinc air cells produce power from internal exposure
to air. When you get the cell is has a sticky tape over a bunch of
holes drilled in one side of the case. Once exposed to air they start
draining but can be stopped again by covering up the holes.
Both silver oxide and mecury hold flat voltage curves until very near
end of life. That's why a silver oxide is much preferred over alkaline.
Chuck Norcutt
Johnny Johnson wrote:
> Hi Folks,
>
> My granddaughter is in need of a camera for a high school photography
> class that's coming up in a couple of weeks and I have an OM-1 that I
> want to donate to the cause. But, the camera hasn't been converted to
> use 1.5 volt batteries yet so I'm looking for alternatives. I
> thought about sending it to John for conversion but his Web site is
> quoting a turnaround of 6-8 weeks which is too long to wait plus the
> foam seals, speed settings and timer all seem to be in fine shape so
> a full CLA doesn't really seem to be necessary. As I remember it the
> rap on the Wein Cells was that they didn't last very long and could
> lead to incorrect metering. I don't remember anything negative being
> said about the C.R.I.S. adapter other than them being somewhat
> pricey. Is the C.R.I.S. adapter my best choice if I can swallow the
> cost and can't wait for John?
>
> As a BTW - the C.R.I.S. adapter uses a silver oxide #386
> battery. Does this battery hold a flat voltage curve over time so
> that I don't have to worry about metering inaccuracies as the battery ages?
>
> Thanks,
> Johnny
>
> __________________________
> Johnny Johnson
> Cleveland, GA
> mailto:jjohnso4@xxxxxxxxxx
>
>
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