My XSi+24-70L Focus Test - Is this acceptable?

I would like help understanding if the following results are "within spec".

The first picture had me worried that I had a small front focusing problem, as the intended focus point is further back in the depth of field than it is in the Live View/Live Mode shot. Indeed, the intended focus point is crisper in the second shot. But is the first acceptable?

I see the same thing with the focus test chart. In number 3 (AF) the depth of field is shifted just a little forward, I think. Not bad, but noticeable to me. The manual focus shot of the test chart (#4) seems to have a perfectly distributed DOF.

So, is everything within spec? Or would you be dissatisfied with these results? I'd like to think I'm nitpicking, but I just can't leave it alone.

Thanks in advance.

Details:

Camera:
XSi/450D, s/n: 032011XXXX
Auto White Balance
Standard Picture Style
Center Point Focus (only)
Evaluative Metering
On Tripod
Remote Release used to fire
All CF set to 0 except #8, which was set to 2 (to enable Live Mode focus)
Manual Exposure Mode (EXIF should be intact)

Lens:
24-70/2.8L
s/n: 1093XXX
date code: UW0212
fully zoomed in to 70mm
wide open ( f/2.8 )
no filters attached

Crops are 100%. Camera was as close as I could get it to 45-degrees (and the subjects were probably about three to four feet away).

#1 - Auto Focus (magazine). Center point was on the "d" in the word "Moondeer" in the line that reads "Moondeer & Friends". 100% crop, center of frame.

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looks like your af is back focusing from me just looking at the pictures and taking nothing into account haha, someone else cant jump in and type a page for you..

Are you shooting wide open? My chart went out of focus in front and behind at the 6mm mark at 60mm f2.8 positioned a little farther out than MFD.

It may be a little off, but probably not enough to cause any problems in real-life shooting. If you start noticing that the focus is consistently off in one direction (e.g. consistently front focusing) in real-life shots, you might want to consider re-calibration.

Alex: Yes, wide open, as stated above. But I was probably 3 or 4 feet away, not the MFD of 1.3 feet. If I get time I'll do another one much closer to MFD.

Jay: That's what I keep trying to tell myself, but it bugs me that my selected focus point is at the very back of the DOF. So if I focus on someone's eye, for example, almost nothing past their eye will be in focus. (I know I'm talking about f/2.8 here, which is a very shallow DOF to begin with, but like I said, I just can't seem to leave it alone.)

Thanks everyone so far. Anyone else?

Re-did the test, but much closer to minimum focus distance, probably about 18 inches away (all other info above is the same unless noted below). To my eye, the results are the same. With standard AF, the intended focus point is toward the back of the depth of field.

Again...is this within spec?

Thanks!!!

#1 - Center of focus chart, 100% crop on right edge of image. Auto Focus.

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Gratuitous self-bump. Would really like to hear what others think.

Thanks!!!

You have any "real life" shots to show if it is a real problem? Doesn't seem like it is to the extreme where it would affect it. Pixel peeping will always find something imperfect. If it bothers you this much as to ask for advice from others just send it in, but there is always a chance to get something back that is worse than what you have now. Canon might just say it is within their specs to and send it back. Take some "real life" shots instead of charts...

I am not a pro so take this with a grain of salt. (I prefer large grain "kosher" salt in my salads).

I think if your camera was misfocusing, the difference between AF and MF would be much more profound.

I also think I read somewhere that the way AF works, more of DOF is supposed to be in front of the intended focus point than behind it. This would be especially profound wide open with a shallow DOF.

I had initial focusing problem when I bought my XTi and when I sent it to Canon they confirmed & fixed it. My MF test chart shots were visibly more in focus on the target line than AF.

Added: Again, somebody correct me if I am wrong, but AF focuses on the area - not a point - and within that area looks for highest contrast. So at a close shot, if 2mm and target lines were both in the target area (2mm is really small distance), there's no telling what AF considered the "right" point to snap to.

I think, if I'm correct, to prove that you have front or back focus, you should print everything but the intended target line in medium gray, have the target line in deep black, so that AF is much more likely to snap to it. Then, if 2mm line is still more in focus, you know you have some front focusing issues.

Amamba wrote in post #5882550
Added: Again, somebody correct me if I am wrong, but AF focuses on the area - not a point - and within that area looks for highest contrast. So at a close shot, if 2mm and target lines were both in the target area (2mm is really small distance), there's no telling what AF considered the "right" point to snap to.

I think, if I'm correct, to prove that you have front or back focus, you should print everything but the intended target line in medium gray, have the target line in deep black, so that AF is much more likely to snap to it. Then, if 2mm line is still more in focus, you know you have some front focusing issues.

I believe you are correct there.

In this set your manual focus looks just like mine at AF with the 6mm marks going a little fuzzy in both directions. I would take the suggestion and reprint with the focus line dark and the others faint to let the AF snap on. But...as was stated the DOF still seems to include your subject even in your tests.

Looks fine. Just throw these tests away and keep them in mind if you drop your body or lens. Enjoy your lens for what it is.

Pixel peeping will make you crazy. Just enjoy your combo, and if you start getting blurry images, THEN resort to looking at things like this.

I used to use this test when getting a new lens/body, and it always seemed to front focus a little. But, I never noticed it in a real picture so stopped worrying about it after obsessing for a long time. I also never post web shots at 100%, nor do I print over 12x18.

Anyway, with an f/2.8 lens the AF is designed to be accurate within 1/3 of DOF, not perfect. It also seems to me canon AF tends to bias a little closer, but I can't prove it. If you are really concerned, take some macro shots and look at them 50%. If everything looks good in those shots, it will never bother you.