Metering the OM-1(N) & OM-2(N)

The OM-1, OM-1N, and the earliest OM-2s (with serial numbers approximately up to 200,000) are center-weighted, measuring the reflected light at a broad central area of the field of view. This is standard for most cameras of the era.

Later OM-2s and all OM-2Ns, on the other hand, average the entire field of view, rather than biasing their reading toward the center of the frame. This is true whether the meter is reading off the shutter curtain (as it does at shutter speeds of 1/45 to 1/1000) or off the film plane (as it does at shutter speeds of 1/45 and slower). (Note that each film may reflect light differently, so expect some variation according to film, but the meter is still averaging the entire scene, whether reading off the curtain or off the film.)

In a way, a meter that averages the entire frame does offer an advantage, allowing you to pay attention and respond to the entire field of view, which is what we normally do when using and trusting our eyes, and photographically, it just might be a more intuitive way of interacting with what is before your eyes in the viewfinder.

So when assessing a scene, if you feel that on average the scene’s highlights, shadows, and middle tones all combine to render a middle reading, then the meter’s suggested reading is going to be sufficient. If you feel that the entire scene either tends toward shadow or highlight, then you have to interpret the meter reading and make adjustments. You can do this with the exposure compensation dial or by shooting in manual mode and adjusting your aperture/shutter speed accordingly.

For example, if you are metering a backlit subject, even if the subject is centered in the viewfinder, keep in mind that the OM-2N meter, reading the entire frame equally, is registering both the centered subject as well as the bright backlit areas at the edges. There are a few ways you can adjust for this:

1. If you are shooting in automatic mode and you know your light well, you can probably tell if the scene calls for a +1 or a +2 exposure compensation, and you can adjust the exposure-compensation dial accordingly.
   1. Or you can pull the camera down to exclude the brightly backlit area, take note of the meter reading, recompose the scene, and dial in the exposure compensation to agree with that previous meter reading.

2. You can switch to manual mode, and if you know your light well, simply adjust either your shutter speed or aperture to account for the bright edges. Or you can pull the camera down, read an area that is not affected by the backlighting, make your shutter speed / aperture adjustments, recompose, and shoot.

3. Or you can use an incident light meter to measure the subject, and either dial that exposure reading in on the manual setting of your camera, or use the exposure compensation dial in auto mode to match the incident-light-meter reading.

Note: The OM-1/1N has one set of meter cells, which read solely off the focus screen. The OM-2/2N, however, has two sets of meter cells. One set, just like the OM-1/1N, reads light transmitted through the focus screen-this set of meter cells controls the meter in your viewfinder display. The second set of meter cells, situated in the corners of the mirror box behind the lens, activate only during autoexposure, and read light off the curtain or off the film plane (depending, again, on shutter speed). These meter cells switch on when the mirror begins its upward journey.

Nothing changes in the OM-2/2N viewfinder meter reading when you switch from manual to auto. It remains exactly the same whether you are shooting in manual or auto mode. In auto mode, there may however be a discrepancy between the reading displayed in the viewfinder and the actual exposure that is finally snapped. This can occur because as the mirror flips up, the two meter cells reading off the curtain or the film may make some final split-second adjustments that the viewfinder can no longer register since the mirror now blocks the light path to the meter cells that control it.