I have a Nikon F that has no diopter. Did not need one when I bought it 30 years ago. I can set the correction needed with my Nikon D500, however, I have no clue how much or little it is correcting my vision. Is there a way to extract that information so I can find/buy the correct diopter needed for my Nikon F eyepiece? Thanks in advance for any and all advice.