Baffling focus issue with Canon EF-S 17-55mm/2.8

Some of you may be aware that I've had long-standing focus problems with my 17-55 lens. The lens has inconsistent AF problems when shooting at distance (for instance, landscape photography). More than half the shots are out of focus, to varying degrees. When the lens mis-focuses, the focal plane is always in front, and sometimes WAY in front, like at the ground in front of me instead of the building I was focusing on.

The lens has been to both Canon Canada and Canon US for service. So far it has completed five trips. Canon says the lens meets all specifications, but when it comes back, it still mis-focuses.

My lens shows the same AF failure on four different bodies, so I don't think it's the body.

My lens is currently at Canon Canada for yet another visit. This time they sent me a loaner lens, another 17-55mm. I got the loaner today and immediately went out and ran some tests. What I found to my amazement is that the loaner shows the SAME autofocus issues as my own lens. It misses focus on distant objects by variable amounts.

This is baffling me, and I could use some input from anyone who knows about lenses and AF.

It seems to me there are three possibilities:

- All Canon 17-55mm lenses have a design flaw that causes variable AF failure when focusing on distant objects (if so, why isn't this generally known?)
- The loaner by coincidence or by clever intent happens to have the same issue as my own lens (seems incredible)
- I don't know what I'm doing (but all my other lenses focus just fine).

So these three possibilities all seem unlikely. But there has to be an explanation.

Suggestions appreciated!!

Here is a recent example of the problem. These two shots were taken seconds apart, on a tripod. They are 100% crops. Below the comparison, the right-hand shot is reproduced uncropped and I think you can see the focus fell on the branches in the foreground.

I can eliminate your option #1. Mine his focus each time very accurately so it's not all lenses. Did you try it with IS both on and off? Just a guess but maybe the IS is affecting the image somehow.

Also, have any filter like a polarizer? Linear polarizing filters affect AF performance.

Which focus points are you using?
Looking at the bottom shot it seems to have grabbed focus on the rocks in the foreground

For all my tests, I use the center AF point only, and don't recompose. No filters were used.

I usually have IS on when hand-holding, but these particular examples were on the tripod, so IS was turned off. IS makes no difference to the AF performance (or lack thereof) of my lens.

what camera body and what shot mode?

troutfisher wrote in post #17538802
Which focus points are you using?
Looking at the bottom shot it seems to have grabbed focus on the rocks in the foreground

The word "grabbed" is a bit of an exaggeration here. The nearer rocks in the extreme lower left corner are indeed pretty sharp. I think the branch that cuts across them is even sharper. So the focal plane is maybe 10 feet away while focusing on a building a mile away.

But this is only in the right-hand shot. Focus was accurate in the left-hand shot. Settings were exactly the same.

The time stamps for these two shots were 12:08:37 and 12:08:41, so four seconds apart.

ksbal wrote in post #17538829
Is this on the 7DII? are you in one shot or ai server or??? Have you tried this on another 7DII body?

Yes, 7D2. One shot mode. It shows the same behavior on my previous 7D and also on an XSi and 40D.

Oddly enough, the focus success rate is much better (but not perfect) on my SL1.

i think i recall one of your threads about this with a distant mountain and a lake in the foreground.

anyway, my first thought after seeing this recent pic was about the lens/camera reporting that focus was achieved. Either that the lens thought it grabbed focus and reported that it did, or that it didn't grab focus but the camera still said "yeah, go ahead and take the pic."

the next thought was that either of those could have happened, and that you might be able to at least get a start on tracking the problem down, by first knowing that the last pic you took was OOF and before doing anything checking to see what focus distance the window on the lens is reporting. Of course, I'm assuming the 17-55 has a focus distance window, even if it doesn't, you could check how close the ring is to the stop point. Generally (and i just checked with my 85mm 1.8) I think that if the lens can't find focus it will park at infinity. I wonder if this changes on a lens by lens basis? Maybe the 17-55 parks at Minimum Focus Distance after not finding focus and there is some breakdown that is making it not be reported correctly to keep the shutter from firing.

and yeah, i know it should be hitting focus, this was just my first random, wishing it was friday thought.

wow, that is a ton of body's that have the same problem.. I wonder if it has to do with what is being focused on?

I think someone posted there is something in the AF manual about times the AF will hit a limitation... was another photo of like a window air conditioner that had some repeating square patterns in it.. Had the same focus issue.

It is a known thing that can happen with AF, and was pointed out in the manual, but I dont' remember where I saw the post.

Does it do the same on say, a light pole?

How does it do on shots other than landscape shots? Lets see some examples of common stuff around your house like the mailbox, the cat, bottle of brew...etc

I hope you get it sorted out, my 17-55mm is a beast and my favorite lens.

So when you're aiming to focus you're pointing it at the distant objects? What happens when you aim for something a bit closer and stopped down? I mean at 17mm and f8 focusing 10ft away will give you from 3 ft to infinity for DOF

Also is there a reason you're shooting it at f2.8?

DreDaze wrote in post #17538939
So when you're aiming to focus you're pointing it at the distant objects? What happens when you aim for something a bit closer and stopped down? I mean at 17mm and f8 focusing 10ft away will give you from 3 ft to infinity for DOF

Also is there a reason you're shooting it at f2.8?

SVT Wylde wrote in post #17538927
How does it do on shots other than landscape shots? Lets see some examples of common stuff around your house like the mailbox, the cat, bottle of brew...etc

I hope you get it sorted out, my 17-55mm is a beast and my favorite lens.

The lens focuses fine at closer distances. It only fails at longer distances.

The reason I'm shooting at f/2.8 is to facilitate testing the lens. The focus failure also occurs at intermediate f stops, but it is not as obvious. I posted an example of normal shooting a few months ago (testing was not on my mind then) showing the focus failure, as Left Handed Brisket recalled.

DreDaze, are you suggesting that I should not shoot in AF but routinely shoot in manual focus and set it to the hyperfocal distance? Is that what you do?

Here is the picture previously posted. It was shot at f/5.6. The AF point was in the center of the pic, on the distant trees, but the sharpest area is on the trees in the foreground.

The treeline in the foreground has better contrast for the AF to lock onto rather than the trees further away. IS could affect the IQ if it was left on whilst on a tripod, but the whole image would suffer not parts of the image.
EDIT
Try shooting a flat brick wall to see if the lens has issues across the frame.

h14nha wrote in post #17538972
The treeline in the foreground has better contrast for the AF to lock onto rather than the trees further away. IS could affect the IQ if it was left on whilst on a tripod, but the whole image would suffer not parts of the image.

Yes, you are right about the relative contrast, but I was using the central AF pt only. Also, I've done many tests with very high contrast subjects as targets and see the same problem. Ergo contrast of the subject is not a factor here.

The lens AF focuses OK about a third of the time, and always focuses OK in liveview in manual focus. So we can conclude that the glass is good.

Thanks for the suggestions.

What I'm really wondering is if anyone else has seen the same problem, or if I'm the only one in the world who has seen it.