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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 12 Feb 2012 (Sunday) 13:46
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EF 24-70 f/2.8L, AF problem

 
TooManyShots
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Feb 13, 2012 10:25 |  #16
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Do a search on the message board, the 24-70L is known to have AF accuracy issue. I had to send mine in to Canon to have them recalibrated. I bought it new too.


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TooManyShots
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Feb 13, 2012 10:26 |  #17
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MGiddings Photography wrote in post #13877215 (external link)
Stop taking images like this it just fuels parania. You cannot test a lens properly this way. Go out and take some real images. If you like them it is OK. If not take it back get another or your money back. To be honest it is the wrong lens on a crop camera and you don't get the what this lens is capable of.


This may be true if you are talking about some other lenses. With the 24-70L, it is known to have AF accuracy issue. Probably it shows up in 3 out of 10 users.


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Andrew_WOT
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Feb 13, 2012 11:45 |  #18

similae wrote in post #13877207 (external link)
Some 70mm shots backfocus slightly, but only 2mm or so.

These variations are expected for phase detection AF.

Lens is clearly backfocuses at 24mm, collect battery test images, make sure to test at others FLs between 24 and 70, send it to Cannon and request adjusting AF at "all zoom positions". They can fix it.
I would also go further at test at 25xFL distance against flat target. You are almost shooting at MFD which is never a good test for AF.




  
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similae
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Feb 13, 2012 14:19 as a reply to  @ TooManyShots's post |  #19

Ok, here's a few real life samples. Larger, uncropped files as links.

1/125, f/4, ISO 400, flash, @68mm, sharpening "3". This one is ok. (ok if we do not discuss WB, exposure, composition etc.. ;) )

IMAGE: http://netti.nic.fi/~miksi79/images/potn/2470/IMG_6430_1024.jpg
IMG_6430.JPG (external link)

1/100, f/4, ISO 400, flash, @70mm, sharpening "1". Focused on left eye (camera left). Distance to subject aprox 2 meters.
IMAGE: http://netti.nic.fi/~miksi79/images/potn/2470/IMG_6400_1024.jpg
IMG_6400.JPG (external link)


1/30, f/2.8, ISO 2000, no flash, @24mm, sharpening "0". Focused on right eye (camera right). Distance to subject aprox 0,8 meters.
IMAGE: http://netti.nic.fi/~miksi79/images/potn/2470/IMG_6434_1024.jpg
IMG_6434.JPG (external link)

I took 117 images and saved 55 of those. The worst ones I have already removed, most of them due bad focus. I was of course fooling around with my new lens so some of bad images are my own fault. Even if I take half to my account it still leaves 30 OOF images. And not all I spared are great either as you can see...

Now I wait and hope I get a better lens back from service. Before weekend hopefully.

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similae
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Feb 15, 2012 00:35 as a reply to  @ similae's post |  #20

jwp721 wrote in post #13878230 (external link)
Don't worry your lens shouldn't be too difficult to correct. I had a similiar issue arise with my 24-70 after about two years of use and now it is my favorite lens and is on my 50D 95% of the time....

Enjoy your 24-70 and be sure to post after you get your lens back.

Thank you, this sounds comforting! I'll post after-service images next weekend (if I have got the lens back)

clintham wrote in post #13878532 (external link)
one of the best bits of software i have ever encoutered. well worth the money - i have confidently and accurately adjusted my 24-70, 70-200 and 50mm on my 5d mkii.

i have so many times to do this manually (batteries and charts just like you!),think i have it right but am never 100% sure. until i used this software. i can wholeheartedly reccomend it. i have the standard version too.

http://www.reikan.co.u​k/focal/ (external link)

Thank you for the tip. Unfortunately 550D is not supported (no microadjustment). Another good reason to buy a new body? ;)

Thanks to everyone else for posting also.


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similae
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Feb 16, 2012 13:20 |  #21

So, the lens and camera are on they way back from service. I called to the service and discussed with the technician who adjusted the lens. He told that the lens had significant front focusing especially in the tele end. Adjusted and tested now. Hopefully UPS delivers them tomorrow, can't wait to try it out!


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similae
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Feb 19, 2012 13:27 as a reply to  @ similae's post |  #22

Re-tested: EF 24-70 f/2.8L, AF problem

So the lens came back friday and I have had time to test it. It seemed to work, but still something in it that makes me unsure if it's ok or not. I took ~300 pics friday evening in school event, but many of the shots seemed to be soft. The lighting was quite dim so I wasn't too worried.

Now I have tested at home and the lens is just perfect when I shoot @70mm. Here's a test shot taken just 1 hour ago, 100% crop from the image. Sharpness =4 in DPP, no other edits. 1/80, f/4, ISO200, ext flash

IMAGE: http://netti.nic.fi/~miksi79/images/potn/2470/eye.jpg

Very good sharpness and focus is just where it should be. Distance to my son was ~ 60cm from sensor. Here's the room where the pic was taken, now without flash. (to give some idea about the lighting conditions)

1/30, f/2.8, ISO1250:
IMAGE: http://netti.nic.fi/~miksi79/images/potn/2470/kitchen.jpg

The problems start when focal length is closer to 24mm. The lens backfocuses nearly every time. Here's a sample:
1/160, f/4, ISO200, ext flash (100% crop, sharpness=3 in DPP)
IMAGE: http://netti.nic.fi/~miksi79/images/potn/2470/backfocus.jpg

The focus point should be in the eye, but it is closer to ear. The distance was ~1 meter, and the problem gets bigger with bigger distance. This backfocusing seems to be related in lower_than_direct_sunl​ight-lighting conditions, but AF should work in normal daylight indoor conditions reliably in my opinion. It does with other lenses at least.

This shouldn't be the normal behavior for this lens, right? Is it possible that AF works worse with my 550D compared to some more advanced body like 60D, 7D etc?

Should I just take this back to store and get a manual focus prime instead... or should I have the right to assume that AF should be better than this with my lens-body combination?

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Andrew_WOT
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Feb 19, 2012 15:10 |  #23

similae wrote in post #13924861 (external link)
The problems start when focal length is closer to 24mm. The lens backfocuses nearly every time. Here's a sample:
1/160, f/4, ISO200, ext flash (100% crop, sharpness=3 in DPP)

The focus point should be in the eye, but it is closer to ear. The distance was ~1 meter, and the problem gets bigger with bigger distance. This backfocusing seems to be related in lower_than_direct_sunl​ight-lighting conditions, but AF should work in normal daylight indoor conditions reliably in my opinion. It does with other lenses at least.

This shouldn't be the normal behavior for this lens, right? Is it possible that AF works worse with my 550D compared to some more advanced body like 60D, 7D etc?

Should I just take this back to store and get a manual focus prime instead... or should I have the right to assume that AF should be better than this with my lens-body combination?

If you consistently get backfocusing at wide end, send it back to Canon for fixing, this is not normal. Accompany your request with sample pictures and demand to fix AF at ALL zoom positions. I've been in similar situation, took a while to square it up.




  
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similae
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Feb 20, 2012 05:09 |  #24

Sent the lens and body back to service. Hope they get it right this time.


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similae
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Feb 22, 2012 12:49 as a reply to  @ similae's post |  #25

I asked technician to call me when he's investigating the problem. Got a call today. He told he found...nothing. Everything is just perfect. AF focuses well in all focal lengths and the lens is sharp. Checked and re-checked.

So I just have to accept that:
- AF cannot work every time.
- AF cannot read my mind
- Not all images are perfect (not even mine ;) )
- I should not pixel peep.

:)

At least I know I couldn't have better 24-70! :D


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Xcelx
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Feb 22, 2012 13:06 as a reply to  @ similae's post |  #26

I've noticed my 5Dc sometimes back focuses under fluorescent lighting and low contrast areas. Maybe low contrast and artificial lighting is the culprit?




  
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similae
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Feb 22, 2012 13:40 |  #27

Xcelx wrote in post #13944450 (external link)
I've noticed my 5Dc sometimes back focuses under fluorescent lighting and low contrast areas. Maybe low contrast and artificial lighting is the culprit?

I'll have to pay attention to this. We have bright LED-lights in kitchen so that is as artificial as it gets..


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Feb 22, 2012 14:06 |  #28

Light sources that flicker will cause AF issues, or at least used to. Canon changed some of the phase detection AF to try to address this in some of the later models. I would think the 550D might be included in that, but maybe not.

Here is a tiny excerpt from a Canon whitepaper on the 5D2, which is supposed to be able to handle this better. The 5Dc certainly would be a victim of this.

"Improved precision over previous AF systems stems from each camera’s ability to adjust for different light sources while calculating focusing distance. Here’s how it works: during Phase Detection AF, the AF engine rapidly measures the density of horizontal and vertical details in a scene and the camera processor uses this data to determine where the sharpest edges and details are located. When found, the AF is locked on target. But under fluorescent lighting and some other artificial lighting sources, a rapid, imperceptible flickering of the light occurs along with sudden color temperature shifts. These tend to throw off the density measurements and therefore the accuracy of the AF calculations. In both the EOS 50D and EOS 5D Mark II, the type of lighting is taken into effect, and readings are averaged and processed with the help of the super-fast DIGIC 4 Image Processor. The result is improved AF accuracy and speed when shooting under lighting conditions that could fool the AF systems found on earlier Canon and competitive models alike."


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Mike ­ K
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Feb 22, 2012 14:28 |  #29

Canon recommends AF calibration tests be performed 25-50X focal length.
for 24 mm zoom position this is with the target 0.6-1.2 Meters and with the 70mm zoom position 1.75 to 3.5M. You are performing your AF testing too close a distance.
Of course Canoncan only calibrate AF at one zoom position, so other positions may be off. The micro calibrate feature in the new 1D X will calibrate a zoom lens at 2 positions and interpolate other zoom lengths.


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Andrew_WOT
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Feb 22, 2012 15:14 |  #30

Mike K wrote in post #13944976 (external link)
Canon recommends AF calibration tests be performed 25-50X focal length.
for 24 mm zoom position this is with the target 0.6-1.2 Meters and with the 70mm zoom position 1.75 to 3.5M. You are performing your AF testing too close a distance.
Of course Canoncan only calibrate AF at one zoom position, so other positions may be off. The micro calibrate feature in the new 1D X will calibrate a zoom lens at 2 positions and interpolate other zoom lengths.

Canon service can calibrate at all zoom positions, but you can't do it via MFA except on 1Dx as you mentioned.

Focusing on wide end against low contrast target in dim light is always a tricky business.
Get under sun, find a flat contrasty target and test there at 25x+ focusing distance.




  
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EF 24-70 f/2.8L, AF problem
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