Herb Chong <[EMAIL PROTECTED]> wrote: >Message text written by INTERNET:[EMAIL PROTECTED] >>>Quote from Herb Keppler's article : >> >>"In other words, unlike film, the bigger sensor area does not necessarily >>produce needed higher resolution. " >> >>Just what has he been smoking? > >Man, he's gonna get a *lot* of mail on that gaffe! > >nothing because there is nothing wrong wiht what he said. larger area >doesn't mean more pixels unless they designed the sensor that way.
But even if a larger CCD *doesn't* have more pixels it will have a higher *analog* resolution (in terms of the number of line pairs that can be resolved across the frame). A full-frame CCD would be 36mm wide and the Nikon D100 CCD is 23.7mm wide. So if you use a lens with a resolution of, say, 50 Line Pairs per Millimeter (I'm picking this value as an example to make the math easier), you'll get a total of 1800 line pairs across the width of the full frame but only 1185 across the width of the D100 frame. For prints, a resolution of 5 lpm is the bare minimum and there's no visual improvement going over 10 lpm. And, using the figures I calculated above, a 10-inch wide print from the full-frame CCD would have a resolution of 7.09 lpm but the same size print from the D100 would have a resolution of only 4.67 lpm. And that's using the *exact same lens*... and CCDs with the *same* megapixel count. This is why many Nikon users report marginal performing lenses in their system don't work well with their digital SLRs. The dirty little secret of digital photography is that the number by which you multiply your focal length (to get 35mm equivalent) is also the number by which you have to DIVIDE your lens' resolution. It's a mathematically inevitable result of using the smaller CCD. Of course, with high quality lenses (better than the 50 lpm in my example) you can get away with dividing your resolution by 1.5 and still get good images. If you use a digital camera with a low megapixel count (effectively having less resolution than the lenses you're using), I suppose the bit about bigger sensors not producing higher resolution might hold true, but most interchangable-lense digital cameras are going to be high megapixel cameras almost by definition. 6 megapixels is going to be the de facto minimum from now on. The idea of using smaller CCDs is attractive in some respects and will always be worthwhile for some people like wildlife specialists, but it'll require a quantum improvement in lens design to get the same image quality we have now with 35mm. The Foveon chip in the Sigma SLR (is that on the market yet?) is so small that you need lenses with 174% better resolution (read that again: 174% better) to get the *same* end resolution as with a full frame. Increasing the megapixel count with a small CCD won't help either. It's sort of like using finer-grained film. You can't get a Pentax 110 camera (or an APS) to produce 35mm-quality images just by using a finer-grained film. (And you can't get medium format results from a 35mm camera that way.) This, rather than compatibility with wide angle lenses, is what's really driving the move to larger CCDs. However: I expect that, even after Canon and Nikon come out with full-frame digital SLRs, they'll continue to make cameras like the D60 (1.6x magnification) and the D1 (1.3x) because the trade-off will be worth while for many photographers like wildlife and sports specialists. In the future, photographers may carry two different camera bodies with different CCD sizes (even if they have identical megapixel count) the way that they now carry camera bodies loaded with different film. (Since you can instantly switch digital cameras from one ISO rating to another and from color to B&W, camera makers need another reason to make photographers buy more than one body and CCD size is a natural way to fulfill this need.) -- Mark Roberts www.robertstech.com
