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Thread: Barrel Distortion in DSLR ?

  1. #1

    Default Barrel Distortion in DSLR ?

    Most DSLRs have a magnification of 1.5x. So in order to get a SLR equiv. of a 35mm, U gotta use a 20mm. Most 20mm have some distortion level, so would I be getting the same level of distortion of a 20mm at 35mm on a DSLR ?

    Similarly, 50mm for film SLR seems to be the most natural, most distortion free range. If u want 50mm on a DSLR, gotta use something like 35mm. WIll I see the distortion of the 35mm lense ?

  2. #2
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    Default Re: Barrel Distortion in DSLR ?

    Originally posted by marcwang
    Most DSLRs have a magnification of 1.5x. So in order to get a SLR equiv. of a 35mm, U gotta use a 20mm. Most 20mm have some distortion level, so would I be getting the same level of distortion of a 20mm at 35mm on a DSLR ?

    Similarly, 50mm for film SLR seems to be the most natural, most distortion free range. If u want 50mm on a DSLR, gotta use something like 35mm. WIll I see the distortion of the 35mm lense ?
    If you use a well-corrected 20mm like a Nikkor AF 20mm f/2.8D, the distortion is next to non-existant. Same goes for the 35. Most camera makers' 35mm f/2 are pretty good.

    Regards
    CK

  3. #3

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    Hmm... I'm not really talking about the quality of lense here. Rather, I'm talking about ... will the inherent barrel distortion of wide angle lenses on the whole, be carried over to a DSLR by a similar extent. Take for example, an average 20mm lense , 18mm or whatever, when viewed on a DSLR with a magnification of 1.5x, will I see similar levels of distortion then on a film SLR ?

    I was thinking with 1.5x magnification, it will be a crop of the original image, magnified to fit the screen. So distortion will still be there, to a lesser extent, but abbeveration (did I get that right ?) would be cropped out in a sense.

  4. #4

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    Dun really understand your question. on DSLR with 1.5x crop factor, the distortion may not be as "bad" as normal SLR. Coz you kinda "crop" away the edges liao lor....

    But as ckiang says, a good lens hv negligible distortion.

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    Hi there...
    I think I get what you mean. The inherent barrel distortion of the wide angle lens will most likely not be visible, because with a DSLR, the viewing angle is less, thus that's why you get the longer focal range. Which means that you only use the part of the lens closer to the centre rather then at the side where the barrel distortion is.

  6. #6

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    Bravo, u got my question.

  7. #7
    Kiwi
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    I tend to disagree with some points here, though I understand what the original question is.

    Yup, I also want to emphasize that barrel distortion is not necessarily inherent in wide angle lenses, especially the higher end ones. For me, I use Canon 20mm lens and distortion is very well controlled.

    If you want to see distortion, get a consumer zoom lens and use it at the wide end. If you fix it to your DSLR, you can still see the distortion even with the focal length multiplication. Mind u, not at the sides, but the center.

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    Originally posted by Kiwi
    I tend to disagree with some points here, though I understand what the original question is.

    Yup, I also want to emphasize that barrel distortion is not necessarily inherent in wide angle lenses, especially the higher end ones. For me, I use Canon 20mm lens and distortion is very well controlled.

    If you want to see distortion, get a consumer zoom lens and use it at the wide end. If you fix it to your DSLR, you can still see the distortion even with the focal length multiplication. Mind u, not at the sides, but the center.
    That's what I am trying to say. Start off with a well-corrected lens like the Nikon or Canon 20mm and whether it went through the 1.5x FLM or not, distortion is minimal if not non-existant. Don't confuse barrel/pincusion/other distortion with perspective distortion which is inherent in all wide angle lenses to a certain degree.

    Here is a full frame 20mm shot. Lines are still straight.



    Regards
    CK

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    With the 1.6X crop by the DSLR both the barrel distortion and extreme wide angle perspective will be gone.

    Take for example;
    If you shot from the same location with a 35mm prime lens on a SLR, are you going getting the simliar result with a 20mm prime lens on a DSLR?


  10. #10

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    Originally posted by jasonpgc
    With the 1.6X crop by the DSLR both the barrel distortion and extreme wide angle perspective will be gone.

    Take for example;
    If you shot from the same location with a 35mm prime lens on a SLR, are you going getting the simliar result with a 20mm prime lens on a DSLR?

    Is this so? I was thinking that the wide angle perspective/DOF exaggeration would still be present, just that the angle of view is cropped.

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    From the same location,

    => on the SLR the angle of view from the 35mm lens=63 degrees.

    => on the SLR the angle of view from the 20mm lens=94 degrees.

    => on the DSLR the angle of view from the 20mm lens=94/1.5 = 62.7 degrees.

    How can anyone still expect to see the same 20mm perspective with just 63 deg angle of view?
    Last edited by jasonpgc; 15th April 2003 at 02:50 PM.

  12. #12

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    Originally posted by jasonpgc
    From the same location,

    => on the SLR the angle of view from the 35mm lens=63 degrees.

    => on the SLR the angle of view from the 20mm lens=90 degrees.

    => on the DSLR the angle of view from the 20mm lens=90/1.5 = 60 degrees.

    How can anyone still expect to see the same 20mm perspective with just 60 deg angle of view?
    Not the angle of view.

    A wide angle perspective also includes the apparent front->back distancing of objects. I was referring to the DOF exaggeration which I doubt would be the same.

  13. #13
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    Originally posted by Zerstorer
    Not the angle of view.

    A wide angle perspective also includes the apparent front->back distancing of objects. I was referring to the DOF exaggeration which I doubt would be the same.
    It will be the same. Can someone with a 1Ds as well as a D30/60/10D verify?

    Regards
    CK

  14. #14

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    If I use a 35mm lense on a FILM/DSLR without MAGNIFICATION and take a shot, I get picture A.

    If I use a 20mm lense, which does have barrel distortion (i.e curvature of the horizon) when used on a normal SLR on a 1.5X DSLR to simulate a 35mm shot on a normal SLR, I get picture B.

    Will picture A be identical to B , in the aspect of distortion? Or will I get more distortion than in B , assuming both are average lenses such that the 35mm has less distortion than the 20mm.

    The reason I'm asking is because, I was thinking if I use a DSLR with 1.5x mag, I will have not choice but to use very high quality wide angles just to get a 35mm shot, which an average 35mm on a Film SLR can give. Its **** loads of money for a good 20mm lense... . If I want a 28mm shot, I must use something like 17mm. Thats like big money.

    THANKS GUYS !

  15. #15

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    you're right marc. To get 28mm shot, you need a ~19mm lens. And as we all know, good super wide angle lens are rare and expensive. it is BIG money unfortunately.

    But think on the other end of the scale. To get 600mm shot, you just need a 400mm lens. Imagine those film brudders hving to buy a monstrous 600mm lens and carry this monster around.

    you win some, you lose some

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    Originally posted by Shadus
    you're right marc. To get 28mm shot, you need a ~19mm lens. And as we all know, good super wide angle lens are rare and expensive. it is BIG money unfortunately.

    But think on the other end of the scale. To get 600mm shot, you just need a 400mm lens. Imagine those film brudders hving to buy a monstrous 600mm lens and carry this monster around.

    you win some, you lose some
    Right. A 300/2.8 probably costs like what, $6-7k? A nice 16-35mm "only" costs you $2.2k. Even the Nikkor 17-35mm costs $2.8k. And your 70 or 80-200/2.8 is now a 300/2.8 "worth" $6-7k.

    Generally, long glass is more ex than wide glass.

    Regards
    CK

  17. #17
    vkm
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    Originally posted by jasonpgc
    With the 1.6X crop by the DSLR both the barrel distortion and extreme wide angle perspective will be gone.
    Originally posted by Shadus
    on DSLR with 1.5x crop factor, the distortion may not be as "bad" as normal SLR. Coz you kinda "crop" away the edges liao lor.
    Distortion isn't necessarily getting better with cropping. All depends on lens design. For example, below is a distortion chart of a very well optimized wide-angle lens (Schneider Super-Angulon XL 5.6/47mm):


    Source: www.schneideroptics.com

    At infinity focus (smooth curve) that lens reaches maximum distortion at about 50-60% image height (corresponding to the "~2x crop factor"). However at macro distances distortion is worst at the corners (dotted curve).

    On the other hand, as CK have illustrated, the distortion is very well controlled and barely noticeable in majority Canon, Nikon, Minolta wide-angle prime and pro-zoom lenses.

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