Focus question with 85mm f1.8/6D

[tevscale]

I recently bought the 85mm f1.8, and am trying to get used to it. I've noticed some oddity with the focusing on my 6D, as demonstrated in the attached shot. I was using center AF point only, and the spot was on the subject's face. The camera reported focus, but it was clearly way off -- focusing on the near shoulder/arm instead.

This is not a consistent problem, as I do get accurate focus sometimes. My one guess is that with the shoulder/arm being so much brighter than the face, that the AF got confused. But can light from that far away from the center of the frame really affect the center AF point?

Thanks for your help and advice.

 

[turbo1168]

Have you changed any of the setting in the C.Fn II: Autofocus menu, especially tabs 2,3 and 4? They dictate how much priority the camera puts on focus accuracy vs speed to release the shutter. Standard settings are tab 2, 0. Tab 3 center and tab 4 center.

 

[tevscale]

I have tab 2 set to 0, and tabs 3 and 4 set to focus priority. Also I should have mentioned I was using one-shot AF. My understanding is that tabs 3 and 4 at least are only relevant for AF Servo.

 

[turbo1168]

Maybe try some focus tests. I'm cheap so have used a piece of lined notebook paper with a sharpie mark across the center line at 30 or so degrees from the camera. Use a tripod and the 2 second timer while focusing on the sharpie'd line. Unfocus and autofocus a number of times from different distances. My 6D has been spot on with every lens I have used including the 85 1.8, my wife's 70D needs AFMA to some degree on all of them. If it is inconsistent, then maybe a lens or body problem.

 

[turbo1168]

And maybe a dumb question... were you using live view or the viewfinder?

 

[tevscale]

Thanks for the suggestion on the focus test. I'll give that a try when I have a chance.

I was using the viewfinder for the shot I posted.

 

[Viggo]

How did you calibrate the lens to the camera?

 

[Northstar]

I recently bought the 85mm f1.8, and am trying to get used to it. I've noticed some oddity with the focusing on my 6D, as demonstrated in the attached shot. I was using center AF point only, and the spot was on the subject's face. The camera reported focus, but it was clearly way off -- focusing on the near shoulder/arm instead.

This is not a consistent problem, as I do get accurate focus sometimes. My one guess is that with the shoulder/arm being so much brighter than the face, that the AF got confused. But can light from that far away from the center of the frame really affect the center AF point?

Thanks for your help and advice.

Tevscale....when I view this image:
1. I don't see anything in focus, and I see you shot at 1/400th, which probably rules out handshake, leading me to believe the plane of focus is behind the subject. Looking at the hand rail, it doesn't ever appear to be in focus as it leads all the way to the OOF subject.

2 I also note that the subject is dark, and the background behind him is dark, which yields little contrast for the AF to detect....always tricky for AF. My guess, and I would emphasize the word guess, is that the AF system had difficulty with this situation, which resulted in the plane of focus to be somewhere behind the subject....maybe the spots of sunlight on the wall directly behind the subject contributed to this.

Just my two cents....and good luck...and welcome to CR!
North

 

[bholliman]

I would certainly do an auto focus test as turbo1168 suggested, maybe this lens needs some AFMA adjustment with your camera body.

I own a 6D and have used a couple of different EF 85mm f/1.8 lenses with it and they always focused great. This lens is noted for its fast/accurate focus ability so my guess would be an lens/body calibration issue. Good luck.

 

[zim]

Hi tevscale, is it possible to post a much higher resolution version of that image? It's way too pixelated to discern anything from it.

Regards

 

[tevscale]

Here's a higher-res version. As for calibration, I haven't done any AFMA, but don't really think that's the issue: I do get some shots where the focus is spot on, but this one missed by a few inches (the focus seems to be on the stitching on the near sleeve)...

 

[StudentOfLight]

On your hi-res upload I'm seeing focus on the edge of the white shirt below the face. Were you half-pressing the shutter button after the camera reported a focus lock or did fully depress the button instantly? If you were half-pressing then perhaps you unintentionally locked onto the high-contrast-edge of the shirt and later drifted onto the eye when taking the shot. If you pushed it down instantly, then given the settings you supplied above it would be a miss-focus.

The problem you've demonstrated is a sample size one one image only though so I wouldn't panic. You can't draw any useful conclusion from a single shot. Test it out in a more controlled manner with repetition. If the problem is consistent then it can be corrected with AFMA settings. If it is inconsistent there may be a hardware issue. The 85mm f/1.8 is the cousin of the 100mm f/2 and 100mm f/2.8 (non-L) macro, so I would assume the AF performance to be very reliable.

 

[alexturton]

I used to ave an 85mm 1.8 and infinity was mislcalibrated so the autofocus got more inaccurate the further the subject distance. Afma only helped me at the distance I calibrated it too.

 

[zim]

Looks like it's front focusing but I'd agree with Student's second paragraph

 

[TeT]

you want to see how it focuses in bright light. See if you have any misses that way first...

That lens is slow to focus in general...

 

[Viggo]

My 1dx is still out for repair, so I'm using the wife's 6D, and have a miss like this with a low contrast subject in shadow with backlight isn't something it will do very well.

I struggle a lot to have proper focus on the 6d and I've run everything through FoCal twice. Without calibration you will never know if your hits are actually misses .

And also remember, the actual focusing point is much bigger than the square you see in the VF.

 

[tevscale]

Thanks again everyone. I did the simple focus test that turbo suggested, and it performed pretty well (if anything it back-focused slightly). I'll get another chance to use it in the real world today (kids' Halloween party) and see how it goes...