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Wide Angle lens / AF question

ArLe


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ArLe Registered since 21st Aug 2002
Thu 26-Sep-02 09:13 PM

Hi Nikonians:

I've posted the following in another forum, but received no feedback. Hopefully someone here can tell me if they've experienced this 'phenomenon' with the Nikon 17-35, or other wide angle lenses.

I recently tried my Sigma 18-35 zoom lens on the D100. In auto focus mode, the lens will focus on the infinity mark at its 35mm position, but does not go all the way to the infinity mark at the 18mm position. Intermediate distances also register differently between the two zoom extremes. Went to Sigma USA, and had them check the lens, and they said all was fine. When it still didn't focus in sync at both ends of the zoom, I asked for a better 'answer'. I was then told that because of the extreme depth of field at the 18mm position albeit 27mm on the D100), the auto focus sensor 'stops' its focus point when it enters the lens' depth of field for that distance/focal length. In 'manual focus' mode, the rangefinder does not show a 'crisp' focus point, but rather a range from the point where the green indicator first comes on and when it goes 'out'.

When I checked my other zoom lens (of course, in the tele range) the focus hits the same mark consistenly (but then again these have much shallower dof).

My question is do owners of the Nikon wide angle zooms experience this same focusing 'phenomenon' or is this just a problem with Sigma wide angle lenses and the Sigma explanation simply 'smoke'??

Sorry for the long post, and thanks for any feedback on this question.

Alan

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