Is there anyone who can help me with the following: I am nearsighted but wear contact lenses to correct this. So I have sharp vision from about 2 meters to infinity and use reading glasses for the rest. However, I prefer viewing the GG of my Bronica ETRSi using the flip-up magnifier without the reading glasses, because this enables me to see the whole area. But that leads to a problem: The standard -1.5 diopter magnifier (at least I think it is the standard magnifier, there is no inscription on it) does not permit me to see a sharp image. This simulates a viewing distance of 26.3" (66.8cm) according to an information page of Tamron (http://www.tamron.com/bronica/prod/etrsi_eye.asp) It has a focusing distance of about 7.5 cm. To correct the problem I sought and found on the internet a +3 diopter lens (focusing distance about 6cm) but this only made the problem worse. Apparently I drew the wrong conclusions from the Tamron site. Is it possible to calculate the right diopter for my situation? I appreciate any help that helps me avoid buying another useless corrective eyepiece.