Quote Originally Posted by LJSLATER View Post
What Bob said.

One quick thing you can try is using the split prism to focus on something at infinity. If the lens and the split prism agree, you're probably good. If you notice a discrepancy, be aware that there are many possible causes, including the lens, mirror, focusing screen, diopter, and your own eyes!

Personally, when I get a picture thatís out of focus or otherwise unsharp, itís almost always because of an error on my part.
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.