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Forum: Pentax DSLR Discussion
09-16-2007, 08:36 PM
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Actually, it's agreeing, but just wording the argument differently. Note, from the article (emphasis mine): "In fact, if the subject image size remains the same, then at any given aperture all lenses will give the same depth of field." But in the case of a smaller sensor, the subject's image size only appears to be the same because when you view the result, you're usually enlarging it to the same size as the full-frame image.
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Forum: Pentax DSLR Discussion
09-13-2007, 09:57 AM
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Of course this is a bit oversimplified -- "identical" is too strong. They will have a very similar field of view, but won't necessarily be exactly the same in other ways.
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Forum: Pentax DSLR Discussion
09-12-2007, 08:01 PM
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It's exactly wrong that you can't compare film and digital lenses on the same camera. So wrong that it's perpendicular to correct. You *can* compare them on the same camera, and they'll look approximately the same.
A 28mm designed-for-film lens will have the same field of view as a 28mm designed-for-digital lens. (There will probably be other differences -- the for-digital lens may be lighter and smaller, and will have different optical coatings.) But if you put that designed-for-film lens back on your film camera body and take a picture, you'll notice that it's much wider. Specifically, what was 46° of the scene in front of you on the digital body is now 65° on film. (Although typically prints are cropped from that by a few percent.)
Yes, this is exactly right.
Nearer to what mark?
It's actually a kind of arbitrary designation, but generally "officially" considered to be the focal length equal to the diagonal of your film or sensor -- which is why Pentax made their 43mm lens, which they tout as "true normal" for 35mm film. The equivalent on 1.5× crop-factor dSLRs is around 28mm. (Despite Pentax's one lens, it is indeed standard to round up to 50mm and 35mm respectively.)
As I understand it, it just happens that at around this mid-range focal length, neither wide-angle distortion or telephoto perspective compression are very apparent at normal print viewing size. There's nothing really magical.
Yes, that part is true. However, the only dSLRs I'm aware of with 100% frame coverage in the viewfinder are Nikon's just-announced D300 and D3. With everything else, a small percentage of the edge of the frame will be captured even though you didn't see it in the viewfinder. (This was common on film cameras too, and matched the practice of not giving you those edges on your prints either.)
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