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02-25-2009, 07:43 PM   #1
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AF and Zoom

If I have a K20D, with:

- a non-motorised lens that relies on the camera's drive (kit, or 55-300 etc)
- a motorised lens that is AF'd by its own drive (sigma, Tamron etc)

will either/both of them maintain focus as I zoom, once focus has been achieved?

Thanks for any advice on this.

Nick

02-25-2009, 08:50 PM   #2
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If you are using AF-C, yes, any AF lens will. Also, if you are zoomed in and focused, zooming out (usually) will be maintain anyway.
02-25-2009, 09:04 PM   #3
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OK. Thanks.

My current non-DSLR's AF will track zoom even when on AF-S. I assume that it throws itself into AF-C during zoom

Is this not so with the K20D? I tend not to use AF-C beccause of battery drag etc....and I assume wear and tear becuse of constant shifting, even when you are just walking around between shots..
02-25-2009, 09:10 PM   #4
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It's more likely you are already focused at infinity. Zooming won't have any effect at that point.

02-25-2009, 09:34 PM   #5
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I don't think that's the case. I can focus quite close up, and then when I zoom I can hear the AF carrying out the adjustment.

The camera actually has a focal distance indicator in the VF. If I zoom out to 100mm 35mm eq, and then focus on something to place the indicator bar about halfway along its travel, and then zoom in, I can hear the AF working and also see the indicator altering to right close up. I also see the image re-sharpening. Within the capabilities of the "macro" minimum distance, the focus in maintained.

It's extremely useful when framing a shot, that then does not have to be re-focused.
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