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Thread: Newbie Question on aperture

  1. #1

    Default Newbie Question on aperture

    If a lense is labelled to have fixed aperture say f2.8, why can we still vary the f value? So what's the different between a f2.8 compared to f2.8-4 lense. Both can achieve 2.8. Does a f2.8-4 means that the maximum f is 4? appreciate if someone can help to clarify my doubts.

  2. #2
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    Default Re: Newbie Question on aperture

    That value is the minimum aperture. It is not a constant aperture.

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    Default Re: Newbie Question on aperture

    Actually depends on how you look at it. Minimum aperture or maximum opening of the lens aperture.

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    Default Re: Newbie Question on aperture

    if a lens is F2.8-4, it means that u can get F2.8 on the wide end and F4 on the tele end.
    Last edited by drumma; 26th October 2005 at 09:54 PM.

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    Default Re: Newbie Question on aperture

    Quote Originally Posted by Jimbo73
    If a lense is labelled to have fixed aperture say f2.8, why can we still vary the f value? So what's the different between a f2.8 compared to f2.8-4 lense. Both can achieve 2.8. Does a f2.8-4 means that the maximum f is 4? appreciate if someone can help to clarify my doubts.
    For the Sigma 17-35 or 28-70mm or 28-105mm, at the 17mm end (for 17-35) or 28mm end (for the other 2), you can shoot at f2.8. At the most tele end (35/70/105mm) however, you can only shoot at f4 widest...
    eat. drink. shoot

  6. #6
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    Default Re: Newbie Question on aperture

    Hello,

    Let's assume your zoom lens is from 70-200mm ya?
    A constant f2.8 means you can use an constant aperture value of f2.8 throughout 70mm to 200mm. This doesn't mean that it's the only aperture value you can use. Depending on the lens, you can use it from f2.8 to f22.

    For a f2.8-4 lens, it means that the minimum fstop you can use at 70mm is f2.8. However, at 200mm, the minimum will be f4 and not f2.8. So in summary,

    for a f2.8 lens,

    at 70mm : 2.8 - 22
    at 200mm : 2.8 - 22

    and

    for a f2.8-4 lens,
    at 70mm : f2.8 - f22
    at 200mm : f4 - f22

    Yeah?

    If it's wrong, please be gentle with me, I'm a book.

  7. #7

    Default Re: Newbie Question on aperture

    i c............ but at what focal length will you not be able to use 2.8 say for 70-200 f2.8-4. at 71mm? Is f2.8 strictly for the lowest focal length for the above example?

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    Default Re: Newbie Question on aperture

    That depends glass to glass.

    Yes, once you leave 70, perhaps to 80, it would hit f/3.2 already.

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