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Olympus manual focus slr light meter troubleshooting

jkfromsk

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Joined
Sep 16, 2025
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35mm
I wanted to find out if the light meter (aperture priority) on my olys were accurate. So i did a lil experiment.

I used a blank white screen as a control variable and the Light Meter app on my iphone to get an "accurate" reading
I tested 200 ISO @ F/2.8 which came out to around ~1/200s

Heres what the cameras measured:
OM-10: 1/125s
OM-2N: 1/60s - 1/100s (?)
OM-2SP: 1/250s
OM-3Ti: 1/200s
OM-4Ti: 1/250s

I suspect there might be something wrong with my 2N, I havent been able to test film yet so im not sure. I could potentially compensate by adjusting the exposure comp knob, but im not sure how this might negatively impact performance
I know that until I test taking photos, I wont know how the camera works, my question is, could it be possible that the measurements will be inconsistent across cameras models and if so, how do i know if it will be accurate?

I am def by no means an expert on these things im mainly a collector who really fell in love with olympus cameras
 
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One ASSumes that the light meter application is 'accurate'. Not necessarily true! I have to use the adjustment feature of the light meter app in my phone in order to get its reading to agree with a known-accurate spotmeter with 0.1EV precision and with the mid-histogram reading (which matches the spotmeter) obtained with my digital camera.

  1. The same app installed on 2 phones from the same manufacturer (succesive models) does not agree with each other, if unadjusted reading, 1+ EV difference in reading
  2. If unadjusted, neither phone agrees with my Minolta Spotmeter F.
phone 1: 1/6 f/2.8 ISO250
phone 2: 1/10 f/2.8 ISO250
spotmeter: 1/15 f/2.8 +0.2EV ISO250 (about 1/20 f/2.8 ISO250)

Keep in mindf that you could be introducing error in the OM-2n simply with the use of a battery other than mercuric oxide cell
...is the OM-2n meter modified, or are you using MR-9 adapter or using zinc oxide cell?
 
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Besides that the light meter app can't be trusted on the OM-2 the indicated speed isn't the actual speed on auto mode. On auto what the camera doesn't care what the meter needle is pointing at. It uses a totally different sensor and measure the light during the exposure.
 
In addition, in Auto mode, all of those cameras except the ON-3Ti meter the light reflected off the film.
So whether or not film is in the camera has a big effect on the exposure.
In manual mode, the metering pattern of the different cameras probably differs as well, and may depend somewhat on the screen you have installed.
wiltw said:
Keep in mindf that you could be introducing error in the OM-2n simply with the use of a battery other than mercuric oxide cell
Click to expand...

All of the cameras on @jkfromsk 's list use modern G13/MS76/357 batteries - no mercury involved.
Only the original M-1 and OM-1 used the 625 mercury cells.
Alkaline batteries that are nearly exhausted might be an issue though.
 
Use Sunny 16 to double check mid day, sunny sky, ASA 125 your camera meters should be 1/125th at F16. If you get same results as with the metering app then I would guess the meter in OM2 needs to be adjusted. But if the error is constant across ISO setting you can adjust the ISO (ASA) setting by one or one and half stops workable as long as your film ISO is in the middle of the pack ISO 100 to 400.
 
wiltw said:
...is the OM-2n meter modified, or are you using MR-9 adapter or using zinc oxide cell?
Click to expand...

Im actually using x2 SR44 batteries. Is this not recommended? I heard it was good since it lasted longer than Li batteries
 

I see, i assumed digital light meter would be pretty accurate.
 

going to give this a shot later today.
so ISO 100 to 400 is the range where you can get away with ASA compensation?
 
MattKing said:
In addition, in Auto mode, all of those cameras except the ON-3Ti meter the light reflected off the film.
Click to expand...

Ah i see, ill probably pop an expired roll in the 2N to try things out
and I also replaced all my batteries recently
 
jkfromsk said:
I see, i assumed digital light meter would be pretty accurate.
Click to expand...

Your meter may or may not be accurate.
I believe that @Chan Tran was referencing the fact that all those cameras except possibly the OM-3Ti have two metering systems.
The one that provides a meter reading in the viewfinder, in case you are using manual mode.
And the separate system that controls exposure in Auto Mode by metering the light bouncing back off the film during the actual exposure.
EDIT: The OM-3Ti also offers OTF Auto Flash metering when used in conjunction with a compatible (usually Olympus) electronic flash.
 
On any OM - Check that as you move the f/stop on the lens that the reading changes by a stop each click. Sometimes the follower gets gummy and doesn’t register the f/stop.

On OM-2 -

I believe the displayed speed and the actual speed can vary especially in auto when the off the film meter circuit controls the shutter. (So you might get the right shutter open time even if the displayed shutter speed in the finder is different).

Of course you can’t test by ear without film because the off the film circuit will see black and give you a real long shutter open time.
 

The results warrant CAUTION, as Sunny 16 is a rough guideline... 'about f/16'
I have metered with a known-accurate spotmeter targeted on an 18% gray card under clear blue sky (at latifiude 38) and gotten readings from a low f/11 +0.2EV (duirng Fall) ranging up to f/16 +0.4EV on various days. Right now, f/16 +0.4EV ((during Fall). Same wide ranging results using incident lightmeter with hemisphere pointed upward at the sun.
 
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jkfromsk said:
going to give this a shot later today.
so ISO 100 to 400 is the range where you can get away with ASA compensation?
Click to expand...
In general, it depends on the camera. I have many old mechanical cameras with dodgy meters. I have a Minolta 100 that is off by 2 stops over but it is almost linear. I compensate by setting 100 ISO film to 25, but shooing say ILford Pan F at 50 which I tested at 25 as my normal E.I for that film I would at the very bottom of the ASA setting at 8, which is not accurate. On the other hand, I have a few camera that read 2 stop under, which means I need to push the ASA up, some of by bottom feeder cameras meters top at ISO 400 or 800 so shooting even a 400 speed film is the a camera 2 stops over will not work. I keep masking tape on the back of my old cameras with how much they need to be adjusted. The trick to test each camera’s meters to see if the error is linear. As you have a nice collection of Olympus bodies I would try and find a tech who can calibrate the meter.
 
One tangential warning: never take the front lens mount off an OM Series camera and start poking around inside. Models like the OM2 have a nylon string to adjust aperture to meter to viewfinder relationships and if one of the geared cogs in this path decides to jump a tooth or completely fall out, the camera is basically only good for parts. Very few repair persons will take on an OM2 with such issues. Ask me how I know...
 
@Kino I know and the bristles of the rheostat brush are like a prickly pine’s bump. You don’t just touch them
 
jkfromsk said:
Im actually using x2 SR44 batteries. Is this not recommended? I heard it was good since it lasted longer than Li batteries
Click to expand...

You're using the right batteries, SR44 (silver oxide) are the batteries specified by Olympus.

Whilst LR44s (alkaline) will fit and work, they have a different discharge curve characteristic and can therefore introduce inaccuracies as the batteries deplete. Neither should Li batteries be used.
 
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jkfromsk said:
I know that until I test taking photos, I wont know how the camera works, my question is, could it be possible that the measurements will be inconsistent across cameras models and if so, how do i know if it will be accurate?
Click to expand...
Yes, their measurements result may vary depend on Metering Mode of cameras, they are some types: Spot (same size with smallest focus circle), 10-15% (circle around focus circle zone), 60% (average from middle focus screen), whole view,...
OM camera bodies have a stage 2 metering system to compensate for light meter, which is quite accurate. Each model will have different pattern but as I inspect, it active all the time (auto mode, manual mode) and will control the final result.



I also own OM-10, OM-2N, OM-4 and they are always -1 -> -1 2/3 EV compared with every my light meters (Pentax digital spotmeter, Pentax Spotmeter V, Minolta autometer 2/3, Sekonic CDS light meter). And guess what, images from OM-2N/OM-4 come out really good (better than OM-10 in some situation). I even use them to shoot Slide film, no regret. Maybe OM-10 is average of entire view, other are somehow tied with 60% from middle zone.
After time I repaired light meter for my friend cameras, I found that TTL light meter somehow always show below EV than any of my light meters, but my friend and I always agree with camera (becuase they produces good output). This is just my conclusion after repairing nearly 20 light meter in camera body (Canon, Minolta, OM,...) and more with handheld light meter (spotmeter, incident light meter).

In your list, there is OM-4TI, If I was you, I would run a roll through it and inspect for negatives, then will use it as standard to calibrate another camera.

P/s: I never trust phone as light meter.
 

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To negate the effect of metering pattern use a target large enough to cover the entire frame and the target must have the same light value all over.
 
Chan Tran said:
To negate the effect of metering pattern use a target large enough to cover the entire frame and the target must have the same light value all over.
Click to expand...

Yes, for calibrating device (in-camera light meter/handheld lightmeter), I always try my best to set up a big enough flat surface with even light value from edge to edge and use my pentax digital spotmeter as trusted reference source.
 
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