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On my Canon kit lens, I could completely zoom in, focus on the object and then zoom out to take the picture with the object still in focus.

Now I have a Sigma 18-200mm (with a Canon 600D) and that doesn't work. After zooming out, focus is lost and I need to refocus.

Is this lens broken or is not every lens the same with focussing combined with zooming?

mattdm
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sanderdatema
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1 Answers1

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The lens is a varifocal lens. Basically, it's a lens that changes focus as the focal length changes and it's quite common. Parfocal lenses, ones that maintain focus on zoom change, exist but are typically more expensive as a result.

Long story short, it's normal for a large number of consumer zoom lenses.

Joanne C
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    is 100% correct. Interesting story on lensrental about a 70-200 lens that is Parfocal, its only $20K http://www.lensrentals.com/blog/2013/04/first-look-zeiss-cz-2-70-200mm-t2-9 – Pat Farrell Apr 19 '13 at 17:15
  • Really? I always thought cheap lenses would do that. I've mostly found it on kit lenses, as the asker has stated. – BBking Apr 19 '13 at 21:55
  • @BBking - most consumer lenses are cheap lenses... – Joanne C Apr 19 '13 at 22:05
  • The Nikkor 10-105 DX is a parfocal kit zoom, although not exactly one of the pits :) – Ryccardo Apr 21 '13 at 12:56