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FORUMS Canon Cameras, Lenses & Accessories Canon EOS Digital Cameras 
Thread started 28 Apr 2012 (Saturday) 12:01
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Shooting
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Apr 28, 2012 12:01 |  #1

Cannot seem to get an answer in the 50D forum for this so maybe someone else here can help. How do I shut off the AF from the shutter button and only use the AF button ON in the back. I want to be able to use the AF ON button on the back to lock in autofocus and then zoom back to get more of the person and then snap it without the shutter button refocusing losing my previous focusing setting.

Thank you.




  
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Tiberius
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Apr 28, 2012 12:16 |  #2

Set Custom Function IV-1 to 2.

This should set it so the shutter button allows for metering, and the AF ON button starts metering and focusing.


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BobOh
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Apr 28, 2012 12:26 |  #3

That sounds right to me, but a follow-up question is in order. Shouldn' t you always refocus when you rezoom?


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Apr 28, 2012 12:49 |  #4

BobOh wrote in post #14343929 (external link)
Shouldn' t you always refocus when you rezoom?

Yes. I can't think offhand of any modern lenses that maintain focus when zoomed.




  
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MakisM1
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Apr 28, 2012 12:58 |  #5

Any of the parfocal lenses. Normally the expensive L-crystal but not necessarilly all of them...

Googling 'Canon parfocal lenses'...

Before I give the list it is worth noting that Canon don't seem to have an 'official' list. They remain silent on this. So any listt like this of Canon lenses is based on peoples own tests and experience and some individuals disagree with some lenses here. For example I have seen discussions where some feel the 70-200mm L IS lens is not parfocal at distances less than 20 feet from the camera - others disagee. So make what you will of the list.

EF 16-35mm f/2.8L USM
EF 17-40mm f/4L USM
EF 24-70mm f/2.8L USM
EF 70-200mm f/2.8L USM
EF 70-200mm f/2.8L IS USM
EF 70-200mm f/4L USM
EF 75-300mm f/4-5.6 IS USM
EF 75-300mm f/4-5.6 III USM
EF 75-300mm f/4-5.6 III
EF 90-300mm f/4.5-5.6 USM
EF 90-300mm f/4.5-5.6


Discontinued lenses in this category include:


EF 17-35mm f/2.8L USM
EF 20-35mm f/2.8L
EF 28-70mm f/2.8L USM
EF 28-80mm f/2.8-4L USM
EF 50-200mm f/3.5-4.5 USM
EF 50-200mm f/3.5-4.5
EF 70-210mm f/4
EF 75-300mm f/4-5.6 II USM
EF 75-300mm f/4-5.6 II
EF 75-300mm f/4-5.6 USM
EF 75-300mm f/4-5.6
EF 80-200mm f/2.8L
EF 100-300mm f/5.6L
EF 100-300mm f/5.6


EF zoom lenses with Super Inner Cam focusing, which include most of the non-L zooms introduced from 1990 onwards as well as the EF 35-350mm f/3.5-5.6L USM and the EF 100-400mm f/4.5-5.6L IS USM, are not parfocal.

by: http://dougchinnery.bl​ogspot.com …anon-parfocal-lenses.html (external link)


Gerry
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oldvultureface
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Apr 28, 2012 14:50 |  #6

MakisM1 wrote in post #14344047 (external link)
Googling 'Canon parfocal lenses'...

Interesting. Thanks.




  
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Maverique
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Apr 28, 2012 14:52 |  #7

I could swear the 24-70 isn't parfocal


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Apr 28, 2012 17:09 |  #8

Tiberius47 wrote in post #14343890 (external link)
Set Custom Function IV-1 to 2.

This should set it so the shutter button allows for metering, and the AF ON button starts metering and focusing.

Hey, thank you so much. I do not have to refocus using the 24-70 2.8 L thank goodness




  
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FlyingPhotog
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Apr 28, 2012 17:20 |  #9

I guarantee the 24-70 and the 70-200 f/2.8L IS are NOT Parfocal.

No Way .. No How


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Tiberius
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Apr 28, 2012 17:23 |  #10

BobOh wrote in post #14343929 (external link)
That sounds right to me, but a follow-up question is in order. Shouldn' t you always refocus when you rezoom?

Yeah. Zoom first, then focus. If you focus and then change your zoom, you should always assume that you are now out of focus unless you have tested it and know for sure that the particular zoom change you have made doesn't result ina focus change.


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