EOS 5D mkII with 24-105mm L f4 AF problems

[20pictures]

My last two jobs using the EOS 5D mkII with 24-105mm L f4 have lost about 50% of the images through poor focus.

I use the centre focus point, one shot, with the expanded 'invisible' AF points disabled. Focus beep enabled & focus search after focus failure disabled. Firmware is updated to 2.1.2 & all electrical connections have been cleaned.

I set up a high-contrast & low contrast subject as a control test. The EOS 5D mkII with 24-105mm find the focus on the high-contrast subject but not on the low contrast subject. If I put the lens on an EOS 5D or EOS 400D it finds the focus on the low-contrast subject. If I put a 50mm f1.8 or 20-35mm zoom on the EOS 5D mkII it finds the focus on the low-contrast subject.

Is there an issue with the EOS 5D mkII with 24-105mm combination using the phase AF? I toggled the IS which makes no difference.

[cale_kat]

At the very least, I have never heard of a camera being infected with a virus but ..........................

I haven't either. I'm speculating, of course, about the cause of any auto focus malfunction. But I'm struck by the high and low contrast test and the differences in test results.

I believe the 5D Mark II has two systems (contrast and phase detection) but only one is available when using the optical viewfinder. I'm not technically knowledgable about the system, so you'll undoubtedly have to correct me, but it seems that the low contrast subject matter does not register on the auto focus sensor with sufficient strength to allow the camera to resolve the focus point. 

The OP also had success focusing on the low contrast subject with different lenses. One lens, a 50mm f1.8, is considerably faster than the 24-105 f4. The other lens was posted with a typo, I believe. The results of this comparison suggests that the lens is to blame. However, when transferred to a different body, the lens works properly. The 5D, however, does not have live view but has a very similar auto focus system. That points to a communications (software) problem between the mk ii body and lens. The 400D test, which also accepted the 24-105 lens without problem, has a different auto focus system. It would be difficult to make a judgement based on this last test.

I have gotten just as far as speculation will take me. I am guessing that the lens is confused by the instructions it has received from the body but have no idea how to resolve this problem.

[20pictures]

Thanks for taking the time to discuss this issue. It's a shame I have not been able to correct the fault.

With regards to my tests the lenses used were:

• CANON EF 50mm f1.8 II
• CANON EF 50mm f1.2L US
• CANON EF 20-35mm f3.5-4.5 (discontinued)
• CANON EF 24-105mm f4L IS USM

There was a typo...!

[ebiggs1]

I am going to fall back to my original suggestion.

"Maybe a C&C by Canon is in order?"

Send it to Canon for a "clean & check".

[20pictures]

OK ...I've sent the lens & the body to Canon to fix the focussing issue.

They contacted me today to say that the lens is giving an Error 01 & that the power diaphragm needs replacing. I'm at a bit of a loss. The fault is a focus issue & I never have any error messages in all the years I have used this lens/body combination. They had stripped & cleaned the lens but I am wondering if they damaged it during the service.

Any comments?

[ebiggs1]

"... I am wondering if they damaged it during the service."

In a word, No.  

[20pictures]

I am curious to know why their service software would show an error that doesn't show on-camera? I assume the error would display on the preview screen but (as said) I have never seen one.

They have yet to test the AF...

[ebiggs1]

They have far more intense diagnostics than your camera does.

[cale_kat]

@20pictures, Your mention of using the focus assist made me wonder if this problem (difficulty locking on in low contrast scenarios) didn't exist before you used the auto focus accessory.

[20pictures]

Yes, it did. The AF Assist was an attempt at a work-around which is why I did not include it in the Control Tests I performed.

[ebiggs1]

"@ebiggs1. I notice that you use Lightroom with your Canon. So an Adobe product is OK but not a Yongnuo product? I'm trying to follow your logic in this example which involves AF electronics."

Sorry, but you really lost me with that statement!  

"I'm trying to follow your logic ..."

Lightroom in no way interacts with the camera.  It can not accurately be described as a camera accessory!  It does not send electronic signals to the circuitry in the camera. Now whether a 3rd party flash is at fault, is not known. I don't use them nor do I recommend anyone else use them. But if it is your cup of tea, more power to ya.