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Thread: Simple Lens Question F2.8??

  1. #1

    Default Simple Lens Question F2.8??

    Hi all,

    we see all the specs on lens and what not.

    they normally give xx mm, F x.x, and some letters depending on what model/make/special functions right?

    i understand the xx mm part what bout the F x.x? i know it refers to the aperture but does it mean that only 1 aperture size can be used only on that lens?

    for eg: Canon EF 14mm f/2.8L USM

    does it meant minimum aperture is 2.8? or if i'm using this lens i can only shoot at 14mm and at F2.8?

    and why is that on the Canon's lens list, i cant find a single lens which offers F8.0? and yet my compact S45 has a F8.0 option? isnt

    and whats the difference between using a telephoto EF 85mm f/1.8 USM lens and a EF 100mm f/2.8 Macro USM lens to shoot macro photography?

    appreciate all helpful answers to a very confused enthusiast.

  2. #2


    Do read this:

    "The aperture on your camera is the diameter of the opening through which the light enters and exposes the film. Changing the aperture of the lens can have a profound effect on the way your picture comes out. Therefore, it is important to have a good understanding of what the aperture will do.

    The aperture is defined on your camera by its f-stop. Which stops your lens have will vary from camera to camera; however, the usual stops are f2, f2.8, f4, f5.6, f8, f11, f16, and f22. The smaller the number of the f-stop, the larger, or wider, the aperture is. In otherwords, f2 is wider, and therefore lets in more light, than f4."

    A lens with a max aperture of f/2.8 can still be closed down (or stopped down) to smaller apertures, e.g. f/8, f/22. The maximum aperture can be used as a rough guide to gauge the quality of a lens, the larger the maximum aperture (the smaller f/number), the higher quality and more expensive the lens is. Lenses are thus named according to their maximum apertures.
    Last edited by Gymrat76; 12th October 2004 at 12:23 AM.

  3. #3


    f2.8 constant means u get a maximum aperature opening throughout the range of ya zoom...u can still use other aperture sizes...normally lens have apertures up to f22..

    eg....28-80 f3.5-4.5 means tt at 28mm the max aperture u can use is f3.5 and at 80mm the max aperture is f4.5 ... not alot of light goin in i would say..

    tt's y ppl call f2.8 zoom lens "fast" lens..more light means faster shutter....but also equates to mean shallower DOF....

    a macro lens normally has a shorter minimum focusing dist...allowing u to take macro shots...normally it also comes with a 1:1 ratio so tt the macro shot u end up taking is not distorted....

    hope this helps...cheers///

  4. #4


    thanks to all

    gymrat was gonna say the site u recommended didnt have anything to do with the question i asked but u edited ur post.... so thx

    i now understand what it all means... heh

    so means for the telephoto lens i use to take macro shots it wont give me a 1:1 output?

    no wonder there are macro lens.

  5. #5


    yup...unless the telephoto u use has got macro function....

    nikkor micro lens serve the same purpose...but it flattens the image..


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