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zoom feature on the DSLR cameras


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#1 Paulo Eduardo Uchoa

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Posted 01 June 2010 - 11:42 PM

I just finished a short film using the canon 5d and one thing that I noticed was that I would measure the distance from camera to subject, match it with the lens then I would double check the focus by using the zoom feature and I found out that I was always off by just a tiny bit. So I am wondering if using the zoom feature makes it seem like I'm doing an imax kinda focus check.
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#2 Hal Smith

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Posted 02 June 2010 - 05:53 AM

I just finished a short film using the canon 5d and one thing that I noticed was that I would measure the distance from camera to subject, match it with the lens then I would double check the focus by using the zoom feature and I found out that I was always off by just a tiny bit. So I am wondering if using the zoom feature makes it seem like I'm doing an imax kinda focus check.


As a rule, still camera zoom lenses are not parfocal, they do not hold focus as the focal length is varied. The Canon EF/EF-S series zooms seem to be better than many others but still not absolutely parfocal.

http://en.wikipedia.org/wiki/Parfocal
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#3 Mei Lewis

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Posted 02 June 2010 - 03:52 PM

Perhaps Paul means the x5 and x10 digital zoom mofe in live view, whic is intended solely for focussing?
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#4 Paulo Eduardo Uchoa

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Posted 06 June 2010 - 12:23 AM

Perhaps Paul means the x5 and x10 digital zoom mofe in live view, whic is intended solely for focussing?


Yes this is the feature that I am talking about. I think is Hal is right about the still lenses, I should do a real test with a PL mounted adapter
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#5 Chris Keth

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Posted 07 June 2010 - 03:22 PM

Yes this is the feature that I am talking about. I think is Hal is right about the still lenses, I should do a real test with a PL mounted adapter


That zoom feature is just a digital zoom in to what is being recorded (but not greater than 1:1). If you're off for that you're soft, period. I don't know your exact rig but with a 5D there's a very good chance that the FFD is off or that your lenses don't tape out properly.
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