NO, this isn't another "what aperature do I shoot an indoor wedding with.." thread. And I'm not new at this. I have no formal training, but I have a pretty good "feel" for how aperature and shutter speed work together. Here's my conflict.... Wikipedia defines the f-stop number as "the focal length divided by the aperature as measured in the same units". So lets take a regular "cheap" kit lens as our sample lens in this scenario. Say a 24-55 f3.5/5.6 is our example. If we take a focal length of 24mm and we know the f-stop is 3.5 max, at that setting, the aperature would be an actual size of 6.86 mm wide. (24mm focal length / 6.86mm aperature opening = f3.5) At the other end, if we take a focal length of 55mm and we know that the f-stop is 5.6, then the aperature would be an actual size of 9.8mm. (55mm focal length / 9.8mm aperature opening = f5.6) My question is thusly: If the aperature can physically open up to 9.8mm at a 55mm focal length, then why can't it open up to 9.8mm at a 24mm focal length? (Which would give us an f2.4 and a faster lens) Do lens manufacturers limit these lenses artifically? Or is there some physical limitation within the lens that I don't know about since I've never taken one apart? (And don't plan to). Does it take more lens elements (and a more expensive lens) to effectively pull off having that large of an aperature at that short of a focal length? If this makes sense to anyone, please help me wrap my head around why this works this way.