robert G. Fately |
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Tonya, there are a couple of things going on here. First of all, apparently there are some Sigma lenses for Nikon that don't play well with the newer DSLRs. As I understand it, it's not every Sigma lens, just certain models. YOu can go to dpreview.com or just Google Sigma/Nikon/firmware or something to find out more. I've neither heard nor seen any instances of a lens "locking down" a D50 altogether, but others here may have better knowledge of that. Now, "digital lenses", or, more succinctly, lenses made for digital SLRs are different in a couple of ways. First, most "digital designed" lenses are made to project a smaller image circle, since the CCD in the Nikon (and most other) DSLRs is smaller than a full 35MM frame. This is what that "cropping factor" thing is about - your 50MM lens has a certain angle of view on the N65; put that same lens on the D50/70/200/2x and the chip, being smaller, does not "see" all of the image the lens is sending back, only the central portion of it. So the 50MM lens "behaves" like a 75MM lens on the DSLR - the crop factor is 1.5. Likewise, the 85MM lens "Behaves" like about a 135MM lens, in terms of the angle of view. Anyway, while a film-oriented lens will always cover the CCD in the DSLR, some newer digital-oriented lenses only cover the CCD area - meaning that if you use it on the N65 you will get some serious vignetting to the edges of the full film frame. The DX line of Nikkors are built this way, as are some Sigmas and other 3rd party lenses. THe other, less discussed (and perhaps less critical) attribute of a digital lens has to do with the rear element being multicoated. Turns out that CCD (and CMOS) chips are more reflective than film, so some of the older lenses can have some flare issues when used on the DSLR. That is, if the lens has a rear element that's prety close to the film plane - if you look at the back of the lens and see the element is 3 inches up the barrel, this is a non-issue. I hope that helps...
January 04, 2006
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