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Thread: f-stop of lens

  1. #1

    Default f-stop of lens

    hi can anybody care to enlighten me on the f-stop of lenses??

    why is it the smaller the small stop the more ex???

    smaller f-stop is used for what actually.

  2. #2
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    Default Re: f-stop of lens

    Originally posted by klein
    hi can anybody care to enlighten me on the f-stop of lenses??

    why is it the smaller the small stop the more ex???

    smaller f-stop is used for what actually.
    The f-stop denotes the size/diameter of the opening of the lens. This is controlled via a diaphram, very similar to how you eye's iris opens and closes.

    f-stop is expressed as f/number, where f is the focal length of the lens. So if you pass you math (no offence ) you will then know that the smaller the number, the bigger the "hole" (aperture). E.g. If you have a 100mm lens, an aperture size of f/2 will measure 50mm (100/2 = 50), and an aperture of f/11 will give you 100/11 = 9.09mm.

    The smaller this opening (larger f-number e.g. f/11), the more depth of field you have. That means more parts of your image will be in focus. Conversely, a large aperture (smaller f-number, e.g. f/1.4) will give you LESS depth of field, perfect for blurring backgrounds.

    By now, you realise that to make a les with a small f-number (large opening), you will need more glass. And not just more glass - more precision and all that is needed in making that lens, so it costs more.

    Regards
    CK

  3. #3
    Gordon
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    with a bigger fstop u can allow more lights to come in and get shots at very dim or limited light areas! And therefore the smaller fstop the more expensive, cos the lens is harder to produce.

  4. #4

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    while a lens with a very small f-stop may seem like a good thing to have in low light, image quality also depends on the quality of optics and the way the lens are arranged.

    big aperture may not produce the sharpest images you can get e.g images may turn out soft at max aperture for certain cameras.

  5. #5
    Senior Member ivor's Avatar
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    Thank you... excellent info for newbie like me...

  6. #6
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    Think you guys got it mixed up a bit.

    Small Aperture = big number = small opening (e.g. f/11)
    Big aperture = small number = large opening (e.g. f/1.4)



    Regards
    CK

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