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10-07-2009, 05:33 PM   #1
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Zoom to Focus

I've been struggling a bit lately nailing focus at wider angles on some of my zooms. Do most of you folks zoom in to focus, then zoom back out and recompose? It seems like I've been getting better results if I take the time to do so. Do a lot of other folks do that?

10-07-2009, 05:44 PM   #2
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It depends on the lens. There are two classes of lens included in the current "zoom" description. The first, correctly called a zoom lens, maintains the focus throughout the zoom range. The other, and more common since the advent of autofocus, is correctly called a "varifocal" lens - the focus may shift during the change of focal length. The word zoom is used for both these days, and that is rather confusing.

If it works for your particular lens is parafocal rather than varifocal, then do it!
10-07-2009, 07:58 PM   #3
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QuoteOriginally posted by Canada_Rockies Quote
It depends on the lens. There are two classes of lens included in the current "zoom" description. The first, correctly called a zoom lens, maintains the focus throughout the zoom range. The other, and more common since the advent of autofocus, is correctly called a "varifocal" lens - the focus may shift during the change of focal length. The word zoom is used for both these days, and that is rather confusing.

If it works for your particular lens is parafocal rather than varifocal, then do it!
Thanks, Albert! It just seems as though it's not -that- far off, but certainly better when focused closer. I think I'll just try to make a habit of it!
10-08-2009, 11:33 AM   #4
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I'm guessing that the cheaper zoom-lenses belong to the varifocal type...which unfortunately means the ones I have.

10-08-2009, 11:37 AM   #5
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QuoteOriginally posted by StarDust Quote
I'm guessing that the cheaper zoom-lenses belong to the varifocal type...which unfortunately means the ones I have.
Not necessarily "cheaper" or "of lesser quality."

Vivitar had some great Series 1 zoom lenses of vari-focal type. So did Kiron (Kino Precision). Their IQ is great because the designers didn't have to compromise so that the lens remained in focus when zooming.
10-08-2009, 07:34 PM   #6
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I understood most modern zooms with autofocus are varifocal. Anyone confirm this?
10-08-2009, 07:50 PM   #7
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They are, just from my experience...
The 16-50, 12-24, 28-75 and 55-300 would all be varifocal given that they're all not IF - and I've tried it myself and seen the need to refocus after readjusting zoom.

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