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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 16 Jun 2010 (Wednesday) 20:29
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Is this lens back focusing?

 
YseanY
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Jun 16, 2010 20:29 |  #1

Is this 35L back focusing?

at 1.4 http://picasaweb.googl​e.com …8pfzieepo?feat=​directlink (external link)

IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO


at 2.8 http://picasaweb.googl​e.com …8pfzieepo?feat=​directlink (external link)
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO


at 4.0 http://picasaweb.googl​e.com …8pfzieepo?feat=​directlink (external link)
IMAGE NOT FOUND
IMAGE IS A REDIRECT OR MISSING!
HTTP response: 404 | MIME changed to 'image/png' | Byte size: ZERO



  
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AWGD8
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Jun 16, 2010 20:41 |  #2

It looks like it backfocus by -1mm which is not much. That -1mm off could be your setup with the tripod angle and the focus chart.


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Tee ­ Why
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Jun 16, 2010 21:42 |  #3

I'd personally keep it.


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xarqi
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Jun 16, 2010 23:02 |  #4

If you are consistently getting this result, then yes, the lens (or the body, or the combination) is slightly back-focusing. Is it an issue? Only you can decide.




  
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YseanY
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Jun 16, 2010 23:39 |  #5

Thanks! I just eyed the 45 degree angle with a folded piece of paper so I'll try to take a few more test shots. I haven't really had much problem with the lens except the last few shots I thought I nailed was not as sharp as I expected so I did the test today. I was debating if I should return/exchange the lens or just not deal with any shipping or restocking and have the lens cleaned and calibrated before the warranty.




  
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Heavy ­ Smiles
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Jun 16, 2010 23:50 |  #6
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Test your lens on a real-life subject ;)


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xarqi
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Jun 17, 2010 01:05 |  #7

YseanY wrote in post #10376681 (external link)
Thanks! I just eyed the 45 degree angle...

The 45° angle is by no means critical. Getting it a bit wrong just means that the scale is not calibrated in true mm.




  
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yogestee
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Jun 17, 2010 09:54 as a reply to  @ xarqi's post |  #8

Looking at your images, where you focused is spot on..

What you have forgotten to factor in is, there will always be slightly more area in focus beyond the point of focus than infront..

This is one reason many landscape photographers will focus just infront of the main point of interest.. This way, they have a greater depth of sharpness all the way to infinity.. This is also dependant on aperture and focal length..


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YseanY
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Jun 17, 2010 12:08 |  #9

yogestee wrote in post #10378591 (external link)
Looking at your images, where you focused is spot on..

What you have forgotten to factor in is, there will always be slightly more area in focus beyond the point of focus than infront..

This is one reason many landscape photographers will focus just infront of the main point of interest.. This way, they have a greater depth of sharpness all the way to infinity.. This is also dependant on aperture and focal length..

so generally this is "normal" or well within tolerance?

and just my knowledge, why is the focus usually beyond the point of focus?




  
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AWGD8
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Jun 17, 2010 12:35 |  #10

YseanY wrote in post #10379281 (external link)
so generally this is "normal" or well within tolerance?

and just my knowledge, why is the focus usually beyond the point of focus?

Research on "HYPERFOCAL FOCUSING" It`s a great subject, but I did my best with my FF body and a Sigma 50mm 1.4 and was tough to get everything sharp from close to infinity. (Landscape shots)
Even when I crank the aperture to max f16, my Sigma 50 copy did not give much details on the pics either.

I bet when you shoot portraits, this tiny mm off won`t matter. Makes sure if shooting wide open aperture, shutter speed is fast enough for hand holding.


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Alamy Creative Collection Contributor.
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stsva
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Jun 17, 2010 12:38 |  #11

You might want to take a look at this and run some numbers to see how it works:
http://www.dofmaster.c​om/dofjs.html (external link)


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YseanY
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Jun 17, 2010 14:20 |  #12

thanks everyone! looking at the depth of field calculator, it seems like the lens is within acceptance/tolerance as the depth of field usually focus just a little further back just a little bit. i think the lens will be kept




  
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yogestee
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Jun 17, 2010 20:02 |  #13

YseanY wrote in post #10379281 (external link)
so generally this is "normal" or well within tolerance?

and just my knowledge, why is the focus usually beyond the point of focus?

Yep,,your lens is within "normal tolerances"..


Jurgen
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Is this lens back focusing?
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