If read the same newsgroup and found some more to consider:
Ryuji Suzuki wrote:
>In article <34A810BB.794BDF32@xxxxxxxxxxxxxxx> Larry English
><lenglish@xxxxxxxxxxxxxxx> writes:
> lots of old cameras and light meters are the same way - the battery
> is supposed to be self-regulating, and the mercury cells were.
>I try to summarize a bit about batteries and metering
>circuits I know. I welcome comments, suggestions, bug reports,
>more info to be added by an email to s11751rs@xxxxxxxxxx. If I
>receive a lot of these, I will make better edited version
>reflecting those comments soon. (This is a quick-cook.)
>Please * do * not * redistribute * this writing without asking me
>anywhere besides this newsgroup since I won't be happy when I find
>fatal mistakes later.
>* Battery Types *
>- Mercury
>A single cell has emf (electromotive force, the voltage a battery
>gives) of between 1.3V and 1.4V depending on additive. Typical
>cells give 1.35V. The emf is stable over its life.
>- Silver Oxide
>A single cell has the emf of 1.5V stable over its life.
>- Alkaline
>A single cell has emf of 1.5V not as stable as the two above.
>- Lithium
>A single cell has emf of 3.0V stable over its life.
>Long life, much less likely to leak, i.e., safe to leave the
>battery in the camera for a long period of time.
>This battery dies rather suddenly. Keep spares!
>- Zinc air
>A single cell has emf of 1.35V stable over its life. (Don't know
>much about this because I don't use it...)
>Some OM-1's are modified to accept 1.5V cell because this service
>had been provided by Olympus (I don't know about now). Even with
>this kind of modification, you should use the silver oxide cell
>instead of alkaline cell whenever possible because the former
>provides much more stable voltage over the life, keeping the
>accuracy of the meter.
>Some cameras need two PX-675, or H-C cells. If these cameras are
>readjusted to give correct readings with 1.5V cells, you have an
>option to use the lithium cell which provides very stable voltage.
>The lithium cell with the same size as two PX-675 is called
>CR-1/3N, DL-1/3N, 2L76BP depending on the manufacturer. Radio
>Shack has one for $4.79.
>* Metering Circuit *
>(I discuss only analog types with a traditional needle meter and
>CdS light sensor. If you have junk cameras you don't need, please
>give me so that I can analyze them to expand this section :-)
>- bridge type
>You adjust aperture and shutter speed to bring the needle at the
>center of the scale, where the needle would sit at when power is
>off. The larger the difference from the proper exposure, the
>larger the needle deflection from the center position.
>I.e., no current flow through the meter when exposure is correct,
>and a plus or minus current flows when exposure is off.
>The reading of the meters of this type are not voltage
>dependent. You can use cheap alkaline cell in place of mercury one
>and still have the equal accuracy.
>However, this is not the type OM-1 belongs to.
>- the type which meter indicates proper aperture
>- match needle type other than bridge type
>If you use a battery with wrong voltage, the error will not be
>as great when the light level is low but will be large under
>bright conditions. There are several variations in the circuit;
>some give more error with slow films, some give more error with
>slower shutter settings, etc. I.e., the degree of the error in the
>reading is fluctuating with various factors and not constant.
>Most of the meter circuit configuration other than the bridge
>balancing type belong here, including: OM-1, SRT series, all
>lock-needle AE cameras. With these cameras, you should use
>proper battery cell to assure that the readings are accurate.
>We often hear things like "this camera gives 2/3 stops off if used
>with a 1.5V alkaline cell" but just shifting the film speed
>setting doesn't guarantee the enough accuracy over the wide range
>of illumination, shutter and aperture settings. If you use this
>method, I strongly recommend that you calibrate your "shift
>factor" for all the film speeds you use, over the wide range of
>brightness before you apply the method to a practical purpose.
>* Battery Converters / Adaptors, Modifying a Camera *
>There are battery adapters which take modern 1.5V cells to emulate
>a PX-675 or any other common mercury cell. Such units commonly use
>Schottky barrier diodes with the proper barrier to drop the
>desired voltage. The voltage drop of a diode is proportional to
>the logarithm of (the current flowing through the diode + some
>constant), therefore not quite constant if the current varies
>widely, which is the case of a CdS light meter. A typical current
>range of a CdS light meter is from the order of microamperes to a
>few milliamperes. [This depends on number of CdS cells, battery
>cells and the sensitivity of the galvanometer. SLR's often use two
>battery cells and two CdS cells to achieve wider range whereas
>rangefinder cameras usually use one battery and one CdS cell.]
>If you measure the voltage supplied by a 1.5V cell with such a
>converter with a digital volt meter, you'll see some value higher
>than 1.35V. This happens in a camera when the CdS sensor receives
>only a little light, but you don't have to worry about it because,
>in such a condition, the meter reading error owing to the voltage
>difference is very small. When the sensor receives plenty of
>light, the meter drains more current so the voltage stays close to
>the 1.35V.
>It's not a good idea to drop the voltage of a lithium cell down to
>1.35V using a few diodes in series. Diodes diminish the stability
>of the cell alone. However, dropping 3V down to 1.35 x 2 = 2.7V to
>substitute two mercury cells is a good idea, because this can be
>achieved with one Schottky diode with proper barrier.
>It is possible to stabilize the voltage supplied to the light
>meter with a voltage regulator. However, this methods require more
>current for the regulator itself than the meter part. This
>certainly shortens the life of the battery especially since a
>small button cell doesn't have a lot energy in it. If you approach
>this way, you have to put this part after the switch and you
>should turn off the switch very often.
>Some cameras don't have a power switch at all. This is because the
>light meter drains only a tiny amount of current when the lens
>(sensor) is properly capped. Some other cameras do have a switch
>but you usually don't have to turn off often, as long as the
>sensor is covered. (Turn off switch when you store the camera.)
>If you have a good craft skill, knowledge of electronics, access
>to a good parts supply (low barrier Schottky diodes are not easy
>to find), and the tools, of course you can modify your camera yourself but
>please be careful not to damage the camera.
>There is another way to compensate the voltage difference: adjust
>the potentio trimmers. You need equipment for calibration this
>way. (Simple enough to make one yourself, but remember you have to
>calibrate over a wide range of light intensity. If you make a
>mistake here, you are making the situation even worse than before!)
>--
>Ryuji Suzuki
>s11751rs@xxxxxxxxxx
>North Dartmouth, MA
WKato wrote:
>
> This is off the rec.35mm group. I seems that Olympus is dedicated to
> supporting its 20 year old design (if it's not too much R&D).
>
> Just got this info from Olympus USA reference my question about battery:
>
> The 1.3 volt mercury battery has been outlawed in most states through
> out the country, due to environmental concerns.
> It is possible, however, to use a 1.5 silver oxide battery in the OM -1
> camera, with the new Olympus Battery Adapter MR -9. The MR -9 fits
> into the battery compartment and reduces both the voltage and amp
> output to the required levels for safe use. The part number is OT3102
> and has a list price of $ 25.08, plus shipping and handling. It can be
> purchased directly from our Parts Departments with a Visa and
> MasterCard. You can call them directly at 1 800 622 6372 ( ext. 1620 ).
>
> Warren Kato
> wkato@xxxxxxx
Richard
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