yes.i have a question for those more knowledgeable than me. ok so say i have two canon ae-1s. both of them have the same 400 iso film in them, but one has a 35-200mm 3.5 zoom lens on it, and the other one has a 50mm 1.8 on it. if i set the aperture on both of the cameras to 5.6, will the shutter speed have to be slower on the ae-1 with the 35-200mm lens on it in order to get the same exposure as the one with the 50mm set at 5.6? i am having this problem with my two ae-1s. i think its because the lens is so long that it needs more light to get the same exposure, even when the zoom is set to 50mm and the aperture is the same.
"Technical Note: With many lenses, their light-gathering ability is also affected by their transmission efficiency, although this is almost always much less of a factor than aperture. It's also beyond the photographer's control. Differences in transmision efficiency are typically more pronounced with extreme zoom ranges. For example, Canon's 24-105 mm f/4L IS lens gathers perhaps ~10-40% less light at f/4 than Canon's similar 24-70 mm f/2.8L lens at f/4 (depending on the focal length)."