HI100@xxxxxxx wrote:
>
> Hi Clinton,
> you may well be right that similar vintage cameras have tight
> tolerance cells, particularly within a manufacturing batch.
>
> In my limited look at this when I was modifying OM1 circuits for silver oxide
> battery use, the three examples I looked at, spaning a wide date range
> (OM1,OM1MD,OM1N) all had somewhat different values and in at least one case a
> different number of resistors as one of the resistors is optional (infinite
> value!) in the circuit.
On the OM-1, for example, R1 is normally between 14K and 15K ohms --
it's got a very wide tolerance (the lowest value I recorded before I
quit bothering was 13.7K). R2 is 10K ohms (the highest I've recorded
was 11.6K), R3 is 7K ohms. R4 was omitted early on -- as you noted, it
had a negligible effect on accuracy anyway. Anything within 5-10
percent of these values will provide meter readings within acceptable
tolerance when the cell wires are of the red-pink-green variety, by far
the most common type. Olympus did supply some "special" cells early on,
but like the wide selection of resistors shown in the original parts
list, they proved to be superfluous.
While looking for my old notes on the OM-1's meter, I came across that
memo regarding the original issue of this thread, body focus distance.
According to this memo, the distance from the pressure plate rails to
the lens mount must be 46.19 +0.01/-0.02mm. Most lenses must be focused
(at infinity) to 46.05 +/-0.02mm. This difference is to account for the
thickness of the film. It goes on to describe the 5 different pressure
plates made for the early OM-1's.
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