Originally Posted by Timmyjoe
How are Rollei diopters rated? Like Leica or like Canon/Nikon? Most old 35mm film cameras came from the factory with a stock eyepiece equal to diopter level -1. I use one stop more positive than that, and where it gets confusing is that Leica rates the diopter I need as a "+1" (because it is one greater than stock), but Canon/Nikon rate the diopter I need as a "0" (because that is the final diopter rating if you add +1 to the stock -1).
How does Rollei rate theirs?
The standard eyepiece is a fairly positive lens, so that the normal eye can see clearly the ground glass just around 50mm below. I don't remember the value but it's something like +10diopters (very loose guess). So an eyesight adjusting lens to replace that is that value plus or minus what you need. I'd love to get one rated at -1.0 but I gave up looking. Fortunately with a WLF one can move one's eyes a bit and it's not bad if you don't need a large correction. A similar situation occurs for the prism finder for the SL66 and not having the correct value for bad eyesight is more of a problem.