TP - OM-2/2N

The OM-2 is an aperture preferred electronic slr. Automatic exposure is calculated by reading light reflected off the first curtain (1/1000th - 1/45th) or the film (1/45th to 19 minutes). Earliest OM-2 had center-weighted curtains.

The 19 minute exposure can be had at ASA 12 (in a coal bin at midnight.) OM-2 low light capability will vary with ASA of the film being used (what the ASA knob is set to). The higher the ASA, the shorter the low light exposure. When set to an ASA of 1600, the OM-2 will have an exposure limit of approximately 20 seconds (not a guaranteed exposure). When using high speed film, you can fool the camera into giving longer low light exposures by setting the ASA knob to it's lowest setting (12).

If you are going to test low light capability of your plain OM-2, put a lens cap on and tape over the eyepiece with black electrical tape. Low light exposure with the 2N is limited to a firm 3.5 minutes (the instruction book says 2 minutes) by the P circuit found in the bottom of the camera. This circuit also forces 1/60th shutter speed during TTL flash pictures. If interested in creative work mixing ttl flash with ambient light, you would have to use a plain OM-2.

As the mirror starts to move up, a switch closes and activates the
circuit built into the mirror box floor. When the diaphragm control
lever starts to move, a second switch (main switch) in parallel with
the first switch (sub switch) also closes. These two switches back
each other up in case one fails. In later production, a more
reliable gold plated switch was used as the main switch, making the
sub switch redundant and unnecessary.

Automatic auto circuit "on" is one of the reasons there is no mirror lock in an Olympus SLR with auto exposure control. If you were to leave the mirror locked up, your auto circuit would always be on and the batteries would drain.
If you have an old style OM-2, (serial number 100,000 to 300,000) do yourself a favor and check the following item. Remove the battery cap and look inside the cap. Oldest production has the inside of the cap lined with a circle of clear plastic tape. This was meant to prevent possible damage to the camera electronics if the batteries were loaded backwards. It was found that it also causes lockup because it depends on the outer edge of the battery to make proper contact with the edge of the battery cap. This was quickly dropped from production. A standard part of the factory repair was to remove this tape on all bodies.
If you have such a cap, please remove this plastic liner. Lift edge up with a pin or tweezers, pull off and clean metal surface with alcohol. You must remove all tape residue, if any.

The meter switch (next to the rewind knob) allows you to choose between "Manual" and "Auto". The "Off" position is actually a modified "auto" setting. At this position, the meter movement is turned off, but if you are somewhat educated regarding available light, you might know that at your setting of f5.6 in bright light you would get a shutter speed of 1/1000 with your asa 200 film. Without turning the meter switch to "auto", you can raise the camera to your eye, focus and shoot. You would get the proper shutter speed in this situation.
As long as there's enough available light to give you a shutter speed above 1/30th, this technique will work. If you had to turn the switch to "auto" first, you would definitely miss the shot.