SLR Focusing Accuracy
I have a bunch of Nikkormat Ftns and a couple of EL's, an EL2, and an FE, among others. Recently I have been wondering if I can just assume that the cameras focus accurately. I noticed in some instances that where the camera has a split screen focusing circle in the middle of the screen, that it will show the image to be in focus at a point where, looking at the surrounding ground glass, the focus point is slightly different on the ground glass. Sometimes I feel that my images could be a bit sharper. My lenses aren't the greatest, but include things like a Nikkor 35-135 and a Nikkor 50mm f1.8 -- not too shabby.
I suppose I could do some critical focusing tests. But if any of the cameras are off, what would be the reason, and is corrective action possible? I guess I just don't know how the focusing mechanism works on an SLR. The lenses are all manual focus.