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

Gymbow wrote in post #17540950
Images as well as the scene are in focus when looking at Live View. The OOF issues only occur when taking images though the view finder under the conditions I described earlier in this thread when I was responding to the OP.

Indeed.

This thread is not about live view focusing, it is not about shooting walls or hyperfocal distance, it is about a specific AF malfunction with this lens. The malfunction is easy to demonstrate and is reproducible for the lenses that exhibit the problem.

I would dearly like to hear from any owner of this lens whether they have noticed the same problem, or alternatively whether they have verified that their copy focuses accurately most of the time when shooting distant subjects with a wide aperture.

Well I've never shot at a distant subject with the lens wide open, but I will in the morning if you would like me to. I have a 7D/XSi so I can try both if you wish..........

h14nha wrote in post #17540980
Well I've never shot at a distant subject with the lens wide open, but I will in the morning if you would like me to. I have a 7D/XSi so I can try both if you wish..........

It would be appreciated!

The AF error (if it is present) varies randomly. About 1/3 are badly OOF, a glance at the pic on the computer and you know it.

I hope yours is good.

Left Handed Brisket wrote in post #17540628
shooting a wall tests for various lens problems that are related to the optics. Bad glass, misaligned elements, or just poor sharpness in all corners.

IMO it won't do anything to help explain or provide a workaround for your focus problem.

edit: the other issue when shooting a big wall is that you would have to have the camera sensor exactly parallel to the wall, both up and down and left to right. It's much harder than you might expect, i know from experience doing copy shots.

This is all correct. There is opportunity for many red herrings when chasing faults with lenses.

Nevertheless, I have done the wall test as best I could, with the lens wide open. I noticed nothing out of the ordinary. The optics of this lens are fine.

However, it has randomly bad AF when shooting distant objects.

I won't post the wall picture since that might distract from the subject of the thread.

gjl711 wrote in post #17540623
You misunderstand. I focused using the phase detect focus through the viewfinder just like normal. Then switch to live view to check the focus and see what it focused on. Each time there was no need to re-focus as it hit the target each time very consistently, it did not miss once. This was true whether focusing close or far at a larg aperture or small.

Well, this is a different angle on the subject. It is interesting, and I might give it a try myself. However, while it is related to the issue some of us are having with this lens, it does not actually address it. Will your lens give consistent sharp results when focusing on distant objects using normal thru-the-lens AF?

Archibald wrote in post #17540960
Indeed.

This thread is not about live view focusing, it is not about shooting walls or hyperfocal distance, it is about a specific AF malfunction with this lens. The malfunction is easy to demonstrate and is reproducible for the lenses that exhibit the problem.

I would dearly like to hear from any owner of this lens whether they have noticed the same problem, or alternatively whether they have verified that their copy focuses accurately most of the time when shooting distant subjects with a wide aperture.

I haven't noticed the problem with my 17-55 so far. But I did have general focus issues not limited to any one lens or distance that turned out to be the body, and these have now been repaired (according to Canon).

I will try to go out tomorrow and test for you.

Archibald wrote in post #17541130
Well, this is a different angle on the subject. It is interesting, and I might give it a try myself. However, while it is related to the issue some of us are having with this lens, it does not actually address it. Will your lens give consistent sharp results when focusing on distant objects using normal thru-the-lens AF?

You still don't understand. I am focusing as normal. not focusing using live view. Once focused I check the focus using live view zooming in 10x to see if the target I choose is in focus. Without fail it is. My copy of the lens is not missing focus.

gjl711 wrote in post #17541237
You still don't understand. I am focusing as normal. not focusing using live view. Once focused I check the focus using live view zooming in 10x to see if the target I choose is in focus. Without fail it is. My copy of the lens is not missing focus.

Do you take the picture and examine it on the computer? That's what matters, not whether live view agrees.

When I shoot with the lens, I get apparent quick focusing, confirmation beep, green dot, the target in the viewfinder appears sharp - everything appears normal until I take the picture and examine it on the computer. Then and only then do I notice that there are a significant number of shots out of focus (severely front-focused).

So maybe I don't understand, but please tell me if you actually take the picture and examine it on the computer.

I believe something happens to the focus (in a significant number of instances) in the moment between focus acquisition and pressing the shutter button all the way.

Archibald wrote in post #17541244
Do you take the picture and examine it on the computer? That's what matters, not whether live view agrees.

When I shoot with the lens, I get apparent quick focusing, confirmation beep, green dot, the target in the viewfinder appears sharp - everything appears normal until I take the picture and examine it on the computer. Then and only then do I notice that there are a significant number of shots out of focus (severely front-focused).

So maybe I don't understand, but please tell me if you actually take the picture and examine it on the computer.

I believe something happens to the focus (in a significant number of instances) in the moment between focus acquisition and pressing the shutter button all the way.

I have taken pictures and looked at them as well but not every time. Checking with live view confirms that the lens has focused. I do not show this behavior. It focuses accurately every time.

Archibald - this must be very frustrating for you. I just noticed this thread and haven't read it thoroughly so my apologies if I'm repeating previous comments. I had a 17-55 years ago with the exact same problem. It was a mystery that went on for some time and occurred with the IS in the on or off position. Eventually the IS failed and I sent the unit in for service. The only reference on the manifest was regarding replacement of IS components so I can't say if something else was done but the problem never reoccurred after that service. The only specific detail I recall from the manifest was a reference to the 3rd group assembly. Hope that provides some help to you.

gjl711 wrote in post #17541496
I have taken pictures and looked at them as well but not every time. Checking with live view confirms that the lens has focused. I do not show this behavior. It focuses accurately every time.

Thanks, JJ, it is very useful to know that you have a copy of the lens that focuses accurately and without issues at long distances.

Ok, I did a quick and dirty test earlier, F8 on the left and F2.8 on the right. It was a quick, hand held shot to test your theory, shots taken seconds apart. I've zoomed in and taken a screenshot so it's not the best of example, but the F2.8 is definitely blurry..........

Just one quick question, if this front focus is as severe as it seems from the posted images, surely you are seeing it in the viewfinder? I'm sure I would notice if the image was that out of focus when I was viewing the image in the VF. Not that that helps with the issue of the lens randomly missing focus on subjects at longer distances.

Alan

I ran some more tests today on the loaner 17-55mm lens that Canon Service provided. I used a tripod, AF center point, IS off, OneShot, ISO 100, and shot at focal lengths of 35mm or 55mm. Here's what I found.

On my 7D2, 15 blurry shots, 4 slightly blurry, 7 sharp. That's 73% failures.
In Live View, I obtained 4 out of 4 sharp results.

I also shot some tests on my SL1 body, same conditions as above. Results were
No blurry shots, 1 slightly blurry, 13 sharp. Only 7% failures.
Also 2 sharp shots in Live View.

All the blurry shots were severely front-focused.

When shooting, I get quick apparent focus lock, a confirming beep, and green AF dot in the viewfinder. The subject looks sharp. The distance scale of the lens does not move when the shutter is released. Everything seems fine while shooting. There is no indication at all of a problem. However, the problem is obvious when chimping and when viewing the results on the computer.

At a zoom of 55mm, most of the results were sharp. At 35mm, most were bad.

When comparing AF and Live View, I noticed that the focus usually shifts slightly and sometimes significantly when going from Live View to AF. I don't know if this means anything.

Like I said, I'm baffled.

Here is an example from today, comparing at 100%. I guess it should be obvious, but AF is on the left and LV manual focus on the right. Straight out of the camera.

h14nha wrote in post #17542031
Ok, I did a quick and dirty test earlier, F8 on the left and F2.8 on the right. It was a quick, hand held shot to test your theory, shots taken seconds apart. I've zoomed in and taken a screenshot so it's not the best of example, but the F2.8 is definitely blurry..........

Interesting.

I don't recall if I mentioned it in this thread, but Canon Service recommended that I shoot at f/22 with this lens ... he said he found that a "greater percentage of shots were sharp" at f/22 when he tested the 17-55mm.

A $1000 lens and he tells me to use it at f/22.

There's actually a veiled admission of fault in his advice.