Originally posted by GoremanX No, the focusing screen isn't the same size as the sensor, so its focusing plane is different.
Sorry if I'm going to appear pedantic, but..... I've re-read what you've written, thought about it, and I still don't understand how this can be the case- otherwise wouldn't you need one focus setting to get a sharp image on the focusing screen, and a different setting to get a focused image on the sensor?
For the focusing screen to have a sharp image on it and for it to be of any use as a focusing screen (even if, as you say, the primary focus is normally done by other means these days), it must, by definition, be in the focal plane of the lens as defined by the position of the sensor (ie the same distance from the lens as the sensor is) and therefore the screen and the sensor must have similar dimensions in order to have the same (or similar) field of view- the only thing I can think of that could influence/alter this would be if there were any other optics between the mirror and the focusing screen- which I don't believe there are?
.....maybe I have a fundamental misunderstanding of the way an SLR works?