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Old Jul 14, 2008, 11:12 PM   #1
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Hi! This is the first extra lens that I've purchased for my new Nikon D40. I know this is a very cheap lens, and I've got it very very cheap. Test pictures are good, however there is something that I wanted to ask here: whenever I focus on something, the distance marked in the focusing scale is longer than the actual distance. I was wondering if it may be due to the fact that this lens is designed for film cameras, or if you believe that this lens may have some problem. Focus is good at all distances and through the whole zoom, just the distance in the scale is quite different from the actual. Thanks for your comments!
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Old Jul 15, 2008, 2:58 PM   #2
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It's probably a vari-focal design (i.e. the distance changes as the focal lenght is changed). Most modern zooms are now like that, relying on the camera AF to focus instead of a true zoom!

-> In the old day of manual focus cameras one can zoom in to focus then zoom out to re-compose, but most zooms now don't keep that feature any more to simplify the construction and to reduce weight... Some Sigmas and most if not all Tokina are still true zoom (i.e the distance scale stayed fixed and constant) so if you need the distance scale to be accurate you may look for them instead

FYI:
http://hyperphysics.phy-astr.gsu.edu...t/zoom.html#c1
http://hyperphysics.phy-astr.gsu.edu...pt/varfoc.html
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Old Jul 16, 2008, 7:26 AM   #3
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That was very interesting, NHL. Yes, this lens need to be refocused as one changes the focal lenght. That responds my question. Thanks!
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