Olympus OM-1n battery

Frank53

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I do know, there are more threads about this subject, but I did not find an answer to my specific question.
I have a OM-1 that I bought in 1974. It was adapted to 1.5V batteries during one of the cla's it had over the years. Recently I bought an OM-1n in very good condition. It came without battery and the seller did not seem to know much about it. I put a PX625 1.5V battery in it and compared the measuring with my OM-1. It appeared to be more or less the same, within half a stop.
Do you think it is safe to assume the camera was adapted to new batteries? Is there another way to find this out?
Regards,
Frank
 

wiltw

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I did a recent test, with an UNMODIFIED OM-1n fitted with genuine PX-625 vs. fitted with PX-625A...the PX-645A caused the meter to think there was 0.5EV more light striking the scene than was actually present.

(there was a url link here which no longer exists)
 
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MattKing

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Frank53 said:
It's alkaline.
Regards,
Frank
Click to expand...
Then it will provide a voltage that slowly changes over time, and corresponding exposure accuracy that changes over time.
 
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Frank53

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So if I interpret this correctly, the difference between correct exposure with a mercury cell (or 1.5V in a modified camera) and a 1.5v cell in an unmodified camera, is only about 0,5 stop?
Regards,
Frank
 

MattKing

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Frank53 said:
So if I interpret this correctly, the difference between correct exposure with a mercury cell (or 1.5V in a modified camera) and a 1.5v cell in an unmodified camera, is only about 0,5 stop?
Regards,
Frank
Click to expand...
Due to the discharge characteristics (voltage) of an alkaline cell, the difference in exposure will vary over the life of the alkaline cell. Mercury (and silver oxide) cells were used originally because of their consistent voltage throughout their usable life. Alkaline cells don't offer that.
 

Rick A

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OptiKen said:
What kind of life do you get out of these batteries in your OM-1?
Click to expand...
I haven't changed the battery in my OM-1 in the last three years, but I don't use it often. I must admit, I have used my camera once in the last three years, but I have taken it out and checked it a couple of times a year to make sure everything works. Surprising enough, the battery never leaked or caused any corrosion, and still works and is accurate. I think I've gone through two Wein cells in the last 7 or 8 years. I always turn the meter off when not in use, and most times, I take a reading and shut the meter off unless the light changes.
 
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Frank53

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In my modified OM-1 is a silver oxide 1.5V. In the OM-1n is a new alkaline 1.5V. The exposure they indicate is more or less the same. So the question is still, is the OM-1n modified or not?
Regards,
Frank
 

klownshed

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If you take off the bottom cover you will see the battery compartment has wires going to it. If it's been modified you will most likely see a diode has been placed inline with the red wire next to the battery chamber. If it's unmodified you will just see wires going to the battery terminals with no diode inline.

It's conceivable that the diode is elsewhere but next to the battery chamber is probably the easiest and most logical place to put it.
 

MattKing

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Frank53 said:
In my modified OM-1 is a silver oxide 1.5V. In the OM-1n is a new alkaline 1.5V. The exposure they indicate is more or less the same. So the question is still, is the OM-1n modified or not?
Regards,
Frank
Click to expand...
Sorry, I was answering or addressing the other observations that arose later in the thread.
Most likely, your camera has been modified. But on the off chance that your new alkaline "1.5V" cell is actually a partially discharged, old alkaline cell, with a voltage that is now down near 1.3V, then it will not have been modified.
You see the challenge that the alkaline cell presents!
 

Ricardo Miranda

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Frank53 said:
It's alkaline.
Regards,
Frank
Click to expand...
You are using the wrong battery as explained above.

The OM-1 series and the OM-2 up to the -2SP can't use a battery that hasn't a stable output, so it has to be mercury, silver oxide or zinc-air battery.
The modification on the OM-1 has always been one to use a different voltage, not to make it "tolerant" to voltage differences as afar as I am aware.
 

wiltw

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Frank53 said:
So if I interpret this correctly, the difference between correct exposure with a mercury cell (or 1.5V in a modified camera) and a 1.5v cell in an unmodified camera, is only about 0,5 stop?
Click to expand...

...when the ambient light being metered is EV10 in intensity... When the ambient light is at other levels, the error may vary!
 

CMoore

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This mod is to make the 1.5V battery work properly.?
You cannot (easily) adjust the meter circuit to read properly with a 1.5V battery.?
Thank You
 

MattKing

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CMoore said:
You cannot (easily) adjust the meter circuit to read properly with a 1.5V battery.?
Click to expand...
You cannot. You need to add a component to drop the voltage, because the meter circuit doesn't have that capacity itself.
If the voltage is wrong, the circuit becomes non-linear.
 

CMoore

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Oh wow.....OK.
I know how to install the diode in the OM1, but have no idea how to Check/Calibrate the meter.
Is calibration something that is best left to a knowledgeable tech.?
Thank You
 

John Koehrer

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Two ways to deal with it if you wish.
Have the camera modified or get a battery adapter to fit the 1.5V silver
battery. It's a plastic adapter with a voltage dropping device in it.
 

wiltw

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John Koehrer said:
Two ways to deal with it if you wish.
Have the camera modified or get a battery adapter to fit the 1.5V silver
battery. It's a plastic adapter with a voltage dropping device in it.
Click to expand...

The 3rd way to deal with it is to use a battery such as sold under the Wein brand, which outputs 1.35v without relying upon the mercuric oxide chemistry.
 

Bill Burk

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wiltw said:
...when the ambient light being metered is EV10 in intensity... When the ambient light is at other levels, the error may vary!
Click to expand...
Might be fun to quantify the error. I've been keeping batteries out of certain cameras lately because I haven't got the modification or calibration done.


I did modify my Rollei 35. I adjusted the slope-intercept until it read Sunny 16 outdoors, and agreed with a handheld meter indoors with a fresh alkaline. but that's not the same as calibrating to any standard light or voltage.
 

wiltw

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One issue is that the amount of error is dependent on BOTH light level and battery voltage. So while I might be able to measure at EV2 and EV10 and EV18, using an alkaline battery that happens to be 1.48V at present, for example, I don't have a good means to control input voltage from the alkaline battery within the alkaline battery's range of 1.25V-1.5V.
 

Bill Burk

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Just makes one want to pull the battery out and use a separate meter.

But of course it would be worth quantifying the magnitude and direction of error at different light levels and voltages...

Because if the error is 'not that bad' I might be persuaded to put a battery in again, purely as an emergency backup or sanity check.
 

Ricardo Miranda

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wiltw said:
The 3rd way to deal with it is to use a battery such as sold under the Wein brand, which outputs 1.35v without relying upon the mercuric oxide chemistry.
Click to expand...
Or to use a simple ZA675 hearing aid battery.
It is a lot better than modifying the camera to 1.5V as that change with a diode isn't going to be linear across the EV spectrum.
There will always be an error at Low or High Light.
 

klownshed

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Ricardo Miranda said:
Or to use a simple ZA675 hearing aid battery.
It is a lot better than modifying the camera to 1.5V as that change with a diode isn't going to be linear across the EV spectrum.
There will always be an error at Low or High Light.
Click to expand...
+1 That's exactly what i do. They're convenient and cheap. I just use an O-Ring (or a cut up hair band around the inside of he chamber) to stop the cell from moving too much.

The wiring in a 40 year old camera is often brittle and delicate, so I've not attempted to fit the diode when there's such an easy solution that requires no modification.

I ordered some zinc air cells from Amazon a few years back. I started receiving postal junk mail for hearing aids before the batteries even turned up!

As for accuracy, the meters weren't perfect even when new and the biggest variable is usually the operator. The reading will change depending on precisely where you point it and also depends on which lens you are using. A wide angle will average more of a landscape scene than a telephoto for example.

There's a reason modern cameras (and late SLRs) have so many metering modes, often producing wide variations in the results. It a camera can't agree with itself, a degree of interpretation surely needs to be applied. ;-)
 
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