Quote Originally Posted by benjiboy View Post
In mirror reflex cameras focusing is dependant on the eyesight of person using the viewfinder because the eye becomes part of the optical system even split image prism screens in perfectly adjusted cameras can be apparently in focus to the user if their eyesight is defective when the image at the film plane is not in focus which is not the case with optical range finders.
I did not know that. You are saying that aligning the split image in my SLR prism is somehow less accurate than aligning the images in a rangefinder because of the acuity of my eyesight? Somehow that does not really make sense to me. In both cases my eyesight is involved. I should be able to align to blurry halves of an image in my SLR viewfinder as well, or not as well as the case may be, as I can two blurry ghost images in a rangefinder spot. Hmmm.