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[OM] Re: OM-1 mercury cells / adapter / recalibration

Subject: [OM] Re: OM-1 mercury cells / adapter / recalibration
From: "Simon Worby" <simon@xxxxxxxxxxxx>
Date: Wed, 20 Apr 2005 13:31:09 +0100
Many thanks to all for all the responses:

Let me summarise the advice/comments:

1. 1.55V silver cells have approximately the same stable voltage/time
patterns a mercury cells.

2. Both the in-camera alteration and the MR9 adapter simply reduce
voltage by 0.2V.

3. The meter cannot just be adjusted to the higher voltage since it
affects the readings differently at different light levels.

4. In spite of (1) (2) and (3) above, "the simple Schottky diode
modification that JH does during a CLA or (the same) that you get from a
CRIS-Cam MR-9 adapter is not perfect.  My recollection is that the meter
can be off by a small amount at the extreme ends of the brightness
range. (CN)" Why? Surely 1.35V is 1.35V whether the source is mercury or

5. "There is actually a much better way of doing this accurately without
a diode, which I have not put on the web. (TH)". Tim, are you prepared
to share the information?

6. In view of (1) (2) and (3) above, and without the answer to (5), for
ultimate accuracy the best advice at the moment appears to be: "You can
get calibrated to one of your new mercury batteries and later convert to
a separate MR9 adapter. (JH)".

7. "I'd say 98% of the time, when I adjust the meter to BV (Brightness
Value) 12 [...], the meter is also spot on at BV 15 [...].  When it is
off at BV15, it is because the cds cells have gone bad. (JH)" seems to
contradict (4) above.

8. "Your resale value would be better with the conversion, per a recent
check @ KEH- and you would still have the remaining Hg cells for your
other cameras (BL)" is good advice, but if it doesn't read correctly,
maybe not. Besides, with in-camera use at about 2 years per battery, and
with no intension of selling the camera (my father bought it new and is
understandably very attached to it), maybe it's not worth it?

9. "'Conversions' done by some other shops [...] often include nothing
more than centring the needle with the eccentric at a mid BV. (JH)" Is
it best, therefore, to buy a diode from Maplin and do it oneself? It
doesn't seem very difficult...

10. The mercury cells my father has are possibly valuable. So the
advice: "Since it would cost you little or nothing to get Colchester
Cameras to convert your OM1 to modern batteries, Simon, why not sell
your stack of mercuries on the auction site? (CB)" is a good idea. But
is it legal to sell them? And how much are they actually worth?

Confused? Join the club!

So I haven't sent the camera off to Colchester yet. In short, I haven't
decided what to do!


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