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Thread: Any difference btw DG lens and Normal Lens

  1. #1

    Default Any difference btw DG lens and Normal Lens

    Got this from Sigma Website :-

    Q. Does Sigma make lenses for digital cameras.

    A. Sigma presently offers a number of lenses designed specifically for digital SLR cameras, which can also be used with 35mm SLRs. They are mostly wideangle and widezoom type lenses with large apertures (e.g. 20mm f/1.8, 24mm f/1.8, 28mm f/1.8, 24-70mm f/2.8, 15-30mm f/3.5-4.5), and feature superior light distribution, so that there is minimal light fall-off or vignetting, even when used at maximum aperture. These lenses are designated DG type, and are part of Sigma's EX series of lenses. Remember that the digital imaging device is generally much smaller than a 35mm negative, so the lens will have a longer "effective" focal length. The conversion factor is generally about 1.5X, so a 14mm lens effectively becomes about 21mm when used on these digital cameras. As a result, there are few choices available for wideangle lenses, or even fast "normal" lenses, for these digital cameras. These new DG lenses help fill this void.


    Does it mean if I bought a 15-30mm f/3.5-4.5 and insert it on my Canon 10D, I will get 15-30mm instead of 24 - 48mm ?????

    Can the people who had used the lens give me an insight?

    Thank You.

  2. #2

  3. #3
    Senior Member
    Join Date
    Jan 2002


    No, the digital SLR has a crop factor. The lens still functions like a 15-30mm lens.... but when shooting the same scene on at 15mm with film and digital and comparing, u will find that the digital camera has captured less of the scene since the sensor is smaller than the 35mm negative. That is the "telephoto" effect referred to. So if the 300D has a crop factor of 1.5X, then all lens attached to it has an "effective" focal length of Xmm x 1.5. In which case, your 15-30mm lens would give you the perspective of a 21-45mm lens lor... it's like not so wide angle. That is also why Sigma has specifically designed lens that are wider to accomodate this cropping effect. And usually ultra wide lens tend to vignette (the 4 corners of the photo are darkened, like viewing through a tunnel) and they claim to avoid this issue with their DG line of lens lor......

    Hope I'm correct in my attempt to explain the crop factor of DSLR........
    Last edited by TME; 18th November 2003 at 08:07 PM.

  4. #4


    Loud and Clear ..... which mean I still get the same limitation lah ...... I tot what so different ....


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