Auto Focus Problem with Canon Lens

Flyinggina

Today I had my 6 week old Canon 24-70 2.8L sent back to Canon. :cry My husband and I did some experiments to check out the operation of the auto focus and think that the lens may suffer from what the fellow at Calumet calls a "back focus" problem. Has anyone else heard of this? Whatever the problem, I have been very disappointed with the lens, especially since it gets such good reviews. And, of course, because I paid a pretty penny for it. The bokeh is beautiful, but softness at the point of focus has spoiled many a shot.

Is it true that Canon lenses are more unreliable out of the box than say Nikon's? This is the second lens I have returned to Canon because of auto focus issues.

I seem to remember reading something by Andy a while ago about how to be sure the lens you buy is a good one but I have been unable to find it using dGrin's search function. If anyone can point me to good threads on the subject, I would appreciate it.

Thanks,

Virginia

ziggy53

Flyinggina wrote:

Today I had my 6 week old Canon 24-70 2.8L sent back to Canon. :cry My husband and I did some experiments to check out the operation of the auto focus and think that the lens may suffer from what the fellow at Calumet calls a "back focus" problem. Has anyone else heard of this? Whatever the problem, I have been very disappointed with the lens, especially since it gets such good reviews. And, of course, because I paid a pretty penny for it. The bokeh is beautiful, but softness at the point of focus has spoiled many a shot.

Is it true that Canon lenses are more unreliable out of the box than say Nikon's? This is the second lens I have returned to Canon because of auto focus issues.

I seem to remember reading something by Andy a while ago about how to be sure the lens you buy is a good one but I have been unable to find it using dGrin's search function. If anyone can point me to good threads on the subject, I would appreciate it.

Thanks,

Virginia

Virginia,

Without seeing your test shots, either links to full res or full sized crops, it's hard to comment about what "you" saw. It is also helpful to provide EXIF and the circumstances of the shot.

I haven't heard about Canon being worse than other manufacturers regarding focus issues, but Canon shooters may be more attuned to, or vocal about, the problem.

If you continue to have problems, consider that your camera may need to be calibrated and adjusted for your lenses.

ziggy53

Flyinggina

Thanks for your comments, Ziggy. I appreciate your taking the time to answer.

I don't think it is the camera. My 70-200L f.2.5 has had no problems at all with the AF. It has performed superbly since I took it out of the box. My 17-85 was rebuilt by Canon under warranty after they conceded that it had a defect. It now does a really nice job for a non-L lens. My little 50mm 2.5 has no problem producing sharp photos with the AF, although the AF does hunt a bit in low light or certain difficult focusing situations.

After I used the 24-70 f2.8L for about 6 weeks to give myself time to learn its strengths and to make any adjustments I needed to get the results I expected, I took a series of shots at a 45 degree angle to a chart with markings on it in order to test where the picture was sharpest when I focused on point 0. If I set the focus manually to infinity then used AF to take the photo at a distance of roughly 6 feet (using a tripod), the sharpest area was consistantly (at different aperatures and f stops) behind the point of focus. It did do better when I immediately took a second shot after it had already focused on the 0.

If there is a problem, Canon will be able to tell when it bench tests the lens. If they say there is no problem, then I will work up some photos to post on dGrin and see if someone on the forum can help me figure out what I am doing wrong. For the moment, I'm betting that the AF need adjustment.

All of that said, your points are well taken. It is always good to consider all of the working parts of a system when things go wrong and, I concede in my case, it is often the photographer and not the equipment that is at fault.

Virginia

mikeb380

Flyinggina wrote:

Thanks for your comments, Ziggy. I appreciate your taking the time to answer.

I don't think it is the camera. My 70-200L f.2.5 has had no problems at all with the AF. It has performed superbly since I took it out of the box. My 17-85 was rebuilt by Canon under warranty after they conceded that it had a defect. It now does a really nice job for a non-L lens. My little 50mm 2.5 has no problem producing sharp photos with the AF, although the AF does hunt a bit in low light or certain difficult focusing situations.

After I used the 24-70 f2.8L for about 6 weeks to give myself time to learn its strengths and to make any adjustments I needed to get the results I expected, I took a series of shots at a 45 degree angle to a chart with markings on it in order to test where the picture was sharpest when I focused on point 0. If I set the focus manually to infinity then used AF to take the photo at a distance of roughly 6 feet (using a tripod), the sharpest area was consistantly (at different aperatures and f stops) behind the point of focus. It did do better when I immediately took a second shot after it had already focused on the 0.

If there is a problem, Canon will be able to tell when it bench tests the lens. If they say there is no problem, then I will work up some photos to post on dGrin and see if someone on the forum can help me figure out what I am doing wrong. For the moment, I'm betting that the AF need adjustment.

All of that said, your points are well taken. It is always good to consider all of the working parts of a system when things go wrong and, I concede in my case, it is often the photographer and not the equipment that is at fault.

Virginia

Virginia, having sold lenses in a local store, I haven't seen any difference in return rates between Nikon, Canon, Leica or any other top notch camera. I do have to say that depending on AF on any lens is a chancy thing. Try focusing manually on your chart from different distances and see what the pix look like. Almost an6ything can confuse an AF lens, even a stray flash of light on the subject. I keep my Canon EOS on Manual Focus for over 90% of my photos. The only time I use AF is when i shoot my grandson running around and just don't feel like focusing, however shooting wildlife, or sports photos I use manual focus and follow focus to keep the subject sharp. To me that is the only sure way of doing it. I have photos of hawks flying taken with a 300mm lens hand held and follow focus and they were sharp.

If I had been given a choice when I bought my camera, I'd have bought one without AF which is one reason I'm back to an old Canon F1 and a bunch of RF cameras. Good luck with your lens.

Michael

Flyinggina

Thanks for the input, Mike. It is reassuring that your experience is that Canon doesn't have more problems with its lenses out of the box than other high end manufacturers. I did get very spoiled with the 70-200 which exceeded my expectations from day 1. I sort of expected to get the same high quality when I invested in another L lens. Ah well.

My husband agrees with you about manual focus. At the moment, AF is much more reliabe for me because I am severely nearsighted. I gather that the problem for me is that my glasses correction is off just a bit plus my eyesight is changing rather rapidly at the moment. In any event, what looks tac sharp to me when I focus manually always (and I do mean always) turns out to be OOF on close ups. :uhoh Of course for distance shots with a high f stop, it is easier to get sharp shots -- which is true even using AF that is not perfect. I have been through one prescription change recently and will be having my eyes checked again in October. This getting older business is not for the faint of heart as many have observed before me.

Thanks again for taking the time to answer. I really appreciate it.

Virginia