photo 101 question about lens diameter

[jann1033]

ok with my whopping giant( to me) 72 mm lens, is the f stop the same as on my 55mm lens...ie is it a fraction of the lens mm? so f5.6 on 72 mm would be a larger actual hole than f5.6 on 55mm? the reason i ask is i could take pictures at 8pm under trees with the 72 and know i couldn't have with the 55. does the larger lens let more light in anyway just by reason of the larger diameter ie more area?

 

[pisco]

Regardless of the size of the front element of the lens the image circle projected on the sensor (or film) is the same size. So the exposure time for f/5.6 is the same regardless of the lens.

 

[boBQuincy]

The f stop is technically the ratio of the focal length divided by the aperture size. The filter diameter doesn't have much to do with f stop except as a relative thing; larger diameter probably = larger maximum f stop *on similar lenses*.

As the focal length gets longer the f stop gets smaller (larger number), this is why many zoom lenses have a smaller aperture at the long end of the range.

f 5.6 should be the same amount of light on any lens *but* it is an approximation (so is the focal length) and some differences are to be expected.

 

[jann1033]

thanks

 

[jann1033]

oops

 

[jann1033]

wrong place