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Thread: Using large aperatures on DSLR

  1. #1

    Default Using large aperatures on DSLR

    Have been wondering now since most dslr have a focal length multiplier and only part of the lens is is used. so will using a f1.0,f1.4, f1.8 50mm lens makes a difference? Cos i feel that the "extra" opening of the lens goes to waste as it is not caputured by the CCD

    anyone can clearify?

  2. #2

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    sorry, should be spelt aperture.

  3. #3

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    Quote Originally Posted by sweat100
    Have been wondering now since most dslr have a focal length multiplier and only part of the lens is is used. so will using a f1.0,f1.4, f1.8 50mm lens makes a difference? Cos i feel that the "extra" opening of the lens goes to waste as it is not caputured by the CCD

    anyone can clearify?
    A DSLR with a focal length multiplier only utilises a portion of the image projected by the lens, but still utilises the entire portion of a lens' optics. Each point in the image, whether in the centre or at the corners, is formed by light rays coming from the entire area of the lens. Try and recall what you learnt in primary school science about lenses.

  4. #4

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    But then what we learned in sec sch, a focused image is a sharp point cos i thought it was cropped verion of the lens initially.
    That is why ppl say that lightfall of and chromatic abbrations are less apprant as it only utilise a portion of the lens.

  5. #5
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    Huh?

    At any rate, yes it is of use, because the same applies whether you use an f1.4 lens or an f5.6 lens. The extra "opening" of the lens is there to throw light across the whole image circle, including the central 1.5 bit.

  6. #6

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    Quote Originally Posted by sweat100
    Have been wondering now since most dslr have a focal length multiplier and only part of the lens is is used. so will using a f1.0,f1.4, f1.8 50mm lens makes a difference? Cos i feel that the "extra" opening of the lens goes to waste as it is not caputured by the CCD

    anyone can clearify?
    The idea of having a larger aperture is to "gather" more light, and also creatively to provide more(larger f-number) or less(smaller f-number) depth of field. So a f/1.0 and a f/1.8 will be different, with the f/1.0 lens giving you a brighter viewfinder, and the ability to reduce depth of field to wafer thin.

    Please remember, a larger aperture does not necessarily give you a larger image circle. a larger lens does. A larger aperture gives you a BRIGHTER picture.

    However, some people do notice some light falloff at the edges of lenses. Especially so in wide-angles. The advantage here of using it on a DSLR is that the smaller sensor size might just exclude the distortion (barrel, pincushion) and also the vignetting.

    Correct me if i'm wrong, this is how i understand it.

    Cheers!
    Last edited by leonzhu; 12th January 2004 at 10:03 PM. Reason: spelling

  7. #7
    Senior Member Ansel's Avatar
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    Well said, Leon.

  8. #8
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    Quote Originally Posted by sweat100
    But then what we learned in sec sch, a focused image is a sharp point cos i thought it was cropped verion of the lens initially.
    That is why ppl say that lightfall of and chromatic abbrations are less apprant as it only utilise a portion of the lens.
    do note that schools sometimes simply issues. as you delve deeper, you'll learn a lot more that will expand your knowledge.

  9. #9

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    Here's an example of a wide open shot taken on a DSLR. The advantage here with a very wide aperture is the ability to use faster shutter speeds but it also means losing considerable depth of field.


    Nikon D1H with 58mm f/1.2 AIS Noct-Nikkor
    1/350th @ f/1.2 on ISO 200

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