Originally posted by Clinton My guess is all of our 135/1.8's will say 1.7. Now if we only had the gear to measure the lens wide open and see what it's aperture really is...
there is a simple way, just measure the grey scale value when you shoot a frame against a uniformly lit wall, and also do the same with an F2 lens, noting also the difference in aperture and shutter speed, this gives you a relitive comparison
the reason it does this is because you probably have the increments in 1/3 stops in the camera body, which is fine.
normally I use 1/2 stop increments, in which case it will show F2 and F1.7.
the question is, does the exposure change between the 2. as I suggested to clinton, take shots at all apertures available (F1.7 and F1.8 specifically and measure greyscale value and compare shutter speeds also,. you may see a change in the lens or you may not.
If you are not sure how to measure the data, let me know and i will do it for you