Quote Originally Posted by naturephoto1 View Post
Regardless of the conversations on other sites or threads, if you question the small to no light loss of using such lenses just meter with your 35mm or medium format camera through the lens alone and/or through the lens with these diopter lenses attached. That will confirm how little light is actually lost. These lenses allow for much greater working distances than the extension tubes or bellows. I assure you you will see little (perhaps 1/6 stop or so) or no change to your meter reading.
TTL metering is exactly what I have been using to make my claims. And in my experience extension tubes give much more working distance than diopters with the same magnification.

Ole, that is very well explained. I agree.