Problem with 24-70 F2.8L USM

Hi all. New to the forum. I just bought a used 24-70 F2.8L USM and noticed that even the center sharpness at 24-35mm F2.8 was poor.

Obviously, the weakest spot in a lens is at the wide end but the difference between pictures is stark and surprising in light of the ISO chart for this lens.

Photos of the wheel were taken in shaded outdoor morning light manually focused on Live View at F2.8 24mm 1/250 (zoomed all the way in on the camera's review screen) and about 40mm F2.8 1/250 and backed away so that the object takes up roughly the same amount of sensor space. The problem only shows up at when the lens is opened up and at infinity. It looks and feels like it hits the focus limiter before it comes to focus from 24-35mm or so.

This may be happening at infinity at longer focal lengths too as the pictures of the tree show. The tree photos are all taken at 50mm infinity with different F ratios starting with F2.8 then F4 then F8. All pics are approx. 100% crops which are then re-sized and compressed for use here. When I stop the lens down, performance between focal lengths is similar.

Is this sort of performance normal for this lens? Is the wider aperture somehow showing up a focus problem that narrower apertures mask? I'm just trying to decide if this should be returned or just sent to Canon. If Canon charges too much, I may as well just pony up for any new ones that are still available considering the price that is common for a used one. Thanks for any input.

By the way, all of the pics were taken from a tripod and are crops taken from close to the center of the image.

Anyone have a guess on this?

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Originally Posted by Mikeinminn

Is this sort of performance normal for this lens?

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Definitely not. It looks very out of focus, even for a 40D.

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Originally Posted by Mikeinminn

It looks and feels like it hits the focus limiter before it comes to focus from 24-35mm or so.

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If it was, that would definitely explain why it looks so out of focus.

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Originally Posted by Mikeinminn

Is the wider aperture somehow showing up a focus problem that narrower apertures mask?

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Yes, the deeper DOF of narrow apertures can fix defocus blur.

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Originally Posted by Mikeinminn

I'm just trying to decide if this should be returned or just sent to Canon.

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I would definitely try to return it first.

Thank you very much, Daniel.

I'll also add that you don't want to test the sharpness of a lens at an ISO higher than 100 or 200 ISO. What ISO were you using when shooting these images?

I just checked my shot settings. It was set at 800 ISO which was probably a holdover from the night before. Oops. Rookie mistake from a rookie :)

Still, the comparison should still be valid since I was just comparing one aperture to another on the same lens. The defocus at infinity was very apparent even on the live view screen, not just in the photos.

Or am I wrong?

Thanks for the input.

If you take a picture of an object at 70mm, then walk toward the object letting it fill about the same amount of area within the viewfinder, how are you focusing at or near infinity?

Actually with the first two (the wheel), I started at 24mm infinity then walked away until the object filled approximately the same amt of the sensor at 40mm. It was not quite at infinity at 40mm, thus the room for accurate focus. The tree was shot all at infinity from the same location at 50mm with F2.8, F4, and F8. The tire was the only one that I moved the tripod for, and only the badly defocused shot was at infinity F2.8. I presented the two types of shot to provide clues as to what might be happening. Perhaps I confused the issue more than I clarified it.

At first, I had thought that the issue was just a focal length+aperture combination issue that might show up only at 24mm infinity. Then I took the 3 shots of the tree and found that even at 50mm infinity the same thing was happening at F2.8 especially. So from this, I gather that it is hitting the focus limiter before it reaches focus. So it's going back to KEH for repair.

I'm still baffled by your testing. Why are you testing a lens's focusing ability at infinity? Before you send it back, do this:

1) Tape a piece of paper with black marker writing on it (big letters) onto a wall. Put as much light on it as you can.

2) Set up a tripod about 10 feet away. To test autofocus, use the center point to focus on the paper. Disengage autofocus and turn the autofocus ring so that it isn't locked onto the paper. Zoom in, turn autofocus on, and focus on the paper again. Analyze the pictures to check for focus accuracy. (Really, you shold do this step several times to get a decent sample size).

3) To check for softness, do the same thing except use Live View x10 to manually focus on the target. Once focus has been achieved, take the picture.

4) Analyze results.

I'm posting results at infinity because that is the only area in which I've found a deficiency. With every other focus test on closer subject matter (which takes in the lion share of the photos I take) the lens did very well using something pretty close to the method you posted except that I used a clock face as a "target". At shorter distances, it focuses very well both in AF and MF. I also shoot outdoors quite a bit so there were plenty of opportunities for more distant shots but I'm usually stopped down to at least F8+ which seems to mask the problem.

So I was very happy with the lens until I was shooting outdoors in lower light and sped things up (F2.8) on a more distant target. That was when the soft photos showed up. They were so soft, I was able to see it on the review screen without any magnification. I tried both auto and manual focusing using live view x10. The only way to get sharp photos from the same location was to change focal lengths enough to get away from infinity or to stop down. Otherwise it seemed close to focus but couldn't quite get there before it hit the limiter. So I tried it again the next day in better light with more time to make sure my results weren't skewed by the limitations of my camera's sensor. The result was unfortunately the same.

Two more questions:

Explain your stabilization. What kind of tripod and ballhead/panhead are you using? What shutter speeds were you using?

A lightweight aluminum Manfrotto tripod (190XDB) with a 190RC2 head with a weight rating of 11 lbs. I was also using a remote to take the pics so I wasn't even touching the tripod at the time and there was no wind. Plus I waited a bit to be sure all vibration was damped. There might have been some shutter vibration because that setup is about as light as I'd want, but it was the same for all of the shots I took and the results were consistent with the pictures I posted.

The two wheel shots were both at 1/250. The F2.8 tree pic was shot at 1/6400. The F4 was 1/4000. The F8 was at 1/1250.

Well, it sounds like you've taken care to eliminate most of the variables that can cause issues during the test. Hopefully someone else can weigh in on this. If it were me, I'm not sure I'd send back a lens for being deficient in a way I would rarely ever use it. Then again, after spending a significant amount of money, it's hard to tell yourself that.

Try to return it first as suggested on the last page. If not, send it to Canon. Mine had the sort of the same problem on my 7D and my two rebels. Using at f/2.8 it worked fine outside using Servo, but anything else it was terrible. Indoors it would never focus where it was suppose to. I sent that thing to Canon 4 times in the year that I had owned it and took the very last time for them to fix the issue. Take photos in RAW and send them in with the lens on a CD to show them what is happening. That's finally what I had to do and it worked. It is now one of my favorite lenses to use! If you have the warranty, use it. Call Canon if under warranty so they will at least pay the shipping and you aren't out anything.

Well, I've called KEH Camera and they said that they should be able to fix it under their warranty at their facility. So in it goes. They will let me know more once they can look it over.

Sean, I thought that one over as well. But ultimately decided that, if they will fix it for free, it should come back better (I hope). I was considering Canon just because they have the best repair facilities + I thought it may just require a little tweak and not too expensive + I was unsure that KEH could do that kind of repair.

But KEH says they can, so that's where I'll start.

Good idea about the photo CD Jayson.

Thanks for the feedback.