Diopters?

[AKsarben]

I have a Bronica SQ-Ai with a metered prism. However, it has a -1.5 diopter on it. I just got it and have a bit of a trouble seeing the shutter speed at the top. I wear glasses, have astigmatism and am nearsighted. Current glasses have bi-focal strength of +2.25 How does one read diopter strength for cameras to come up with one that works right?

Thanks!!
Vern

 

[petrochemist]

They're additive. So converting -1.5 to +2.25 needs +3.75.
Won't do anything for your astigmatism though...

 

[AKsarben]

I found this eBay offer and bought a -3.5 diopter. According to Bronica and also Nikon, if I have a -2.00 (myopia - near sighted) prescription glasses that correct for my vision, then the equivalent diopter I would need would be -3.5. My right eye is actually -2.25 so the -3.5 diopter will be loads better for me to see than the same as "plain" glass of the standard -1.5 Here is the link I found : Bronica Diopter For ETR, SQ or GS-1 New Just before I found this I also seen something similar at Nikon.

 

[AKsarben]

I got in the -3.5 diopter and NOW I really can't see anything in the view finder! So, Petrochemist is absolutely right. On my prescription I have bifocals that have a +2.25 for each eye, allowing me magnification to see to read and type. Sending this one back to Jimmy Koh (what a NICE guy!) and exchange for a +1.5 diopter that will probably be just about right.