I have been playing with spot metering on am OM-4T, and I've been finding that while it gives reasonable results when the "spot" is darker than average, it seems erratic when the "spot" is lighter than average.Occasionally it seems ok, but most of the time it doesn't change from the average, and sometimes it goes the wrong way -- it increases the exposure on the bright spot! Has anyone else had this problem, and might it indicate some kind of defect?
The camera does not know what you are trying to get an exposure value for. If you take a spot metered measurement of a highlight, the camera will suggest an exposure that would be correct for an 18% grey object and you will get an incorrect exposure (underexposed). If you take a spot measurement of a shadow area, the camera will suggest an exposure for an 18% grey object and you will get incorrect exposure (overexposed). The actual results would depend on the type of film, lighting conditions, etc. If the scene that you want to photograph is very light, and you want to take a spot measurement, you will have to compensate by adding more exposure. How you compensate is up to you to decide.
I WANT the spotted area to be grey -- not bleached out. Example: the view through a small bright window in a dimly lit room. The window, though small, is larger than the spot metering area. Nevertheless, my spot metering of the window continues to give the average exposure for the room, which would make the window a featureless white blob. If, on the other hand, I have a largish window but want to exposure for the room, I can spot on a dark area of the room and get a couple of stops increased exposure, which is what I expect and want. So, to summarize, my spot meter appears to work on dark areas, but not on light areas.
Do you have any other camera or meter to check it against?
Not with spot metering capability. Regular metering is right on against my OM-1. I've been trying to analyze what's going on. When you press the spot button, the shutter speed bar drops off to the far right and then comes back to its final lock point. But this point will never (or almost never) be further to the left than the reading before you pushed the spot button. It acts as though something is preventing it from moving further. You can force it further to the left (faster shutter) by pressing the shadow button, but I believe this is just making an automatic 2 2/3 stop correction and is telling you nothing about the correct exposure of the spotted region.
What ISO Speed is the meter set at? I ask this because I had an OM-4T that I was shooting some Panatomic-X with recently. I had set the meter at 32 and noticed that i was getting readings for a very fast film speed. I moved the film speed dial from the fastest to the slowest settings several times and then everything started to work properly. Probably it was not making a good contact.
It shouldn't matter if your OM-1 doesn't spot meter. In even lighting the exposure values won't matter. Use the OM-1 to take a reading of of a white sheet of paper that is close enough to the camera to fill the viewfinder and then take a spot reading with the OM-4T of the same sheet of paper in the same lighting and compare the two readings.
Alas, if the white sheet fills the viewfinder field, center-weighted and spot readings are the same, and everything is copacetic. If it doesn't fill the viewfinder field, we're back where we started.
You also need to have film loaded in the camera for everything to work properly.
Well, yes. Effect is independent of aperture or ISO setting and is seen in both manual and automatic operation.
Yes, make sure you spin the ISO dial fully, now and then, and the meter does need film in to read properly.