Need help please! Defective AF on my new L lens?

Hi there,

I just bought a BNIB 24-105mm L4 from a forum member. Apparently he bought a 5D kit from ebay, and sold this lens in its original packaging. He did not open the packaging at all. Before we get to the test images, I have a question:

A. In this situation, will Canon honor the warrantee? I have the blank warrantee card--it has nothing filled in previously. If there is a problem with the lens, can I just send it in to Canon to be adjusted?

B. Okay, let's get to the images. It may just be my imagination. I'm new to SLRs and high quality cameras, so I don't know how much tolerance there should be. But here are low-res pictures of the images we will be comparing:

24-105mm_L_ORIG
24-105mm_L_zoomed_ORIG
50mm_1.8_ORIG
efs_17-85mm_ORIG
efs_17-85mm_zoomed_ORIG

Now, all pictures were taken on my 40D at f/7.1. The built-in flash was used at Av mode. The camera was mounted on a tripod at ~45deg (eyeballed) as prescribed, and a remote was used to actuate the shutter. I estimate the lens to be ~1.5ft from the focus point. The AF pattern was selected for the center box only, and I tried to make sure the focusing area to be exactly in the middle of the focus box, as best as I could.

I've included images from my 2 others lenses as well. The idea being that if the other images are fine, then it's not my camera's fault but the lens. Now here are high-res crops of the originals:

24-105mm_L_CROP
24-105mm_L_zoomed_CROP
50mm_1.8_CROP
efs_17-85mm_CROP
efs_17-85mm_zoomed_CROP

I want to give my notes after I hear your opinions, as I don't want to skew your thoughts.

Please help me out!--this lens is terribly expensive for me, so I need to know if my copy is good or not, and what I can do about it if it is not.

Thank you very much,
Dean

Hi Dean,

I see a bit of CA (I think) on the second Crop photo, but not sure if that's normal behaviour for the 24-105 at 7.1

In real world shots how is the lens performing? Try also manual focusing using live view 10X magnification at a flat object perpendicular to your camera and then see if when you press the AF on button, the camera focuses differently, or take photos of MF vs AF and see which is better

smorter wrote in post #5950266
Hi Dean,

I see a bit of CA (I think) on the second Crop photo, but not sure if that's normal behaviour for the 24-105 at 7.1

In real world shots how is the lens performing? Try also manual focusing using live view 10X magnification at a flat object perpendicular to your camera and then see if when you press the AF on button, the camera focuses differently, or take photos of MF vs AF and see which is better

hi... yeah, the reason i started doing these tests were because i suspected there were af issues with my camera or my other lenses. it just seemed to me that my pictures were not as sharp as they could be. so then i bought this L lens thinking that it would be a drastic improvement, but actually when i zoom in really closely, it is not that different from my kit lens the efs 17-85mm.

i don't think it's the camera anymore, cause as you can see, the test with the 50mm prime lens is almost perfectly focused. and also very sharp. however, it worries me that this $80 lens seems so much sharper than my $400 kit lens or the $1000 L lens. also, sorry, excuse my newbie-ness, but i don't know what CA is. but if you mean the color sepration where you can see some red and green outlining the letters, yeah, i see that quite a bit incidentally on the tests for the efs and the L zoom lenses. i wonder if that is normal too.

hmm, i haven't played with the live view much. i think i'll try your suggestion...

A comparison with the 50mm f/1.8 II is too hard a benchmark for the 24-105 in my opinion. Even though it's cheap the 50mm f/1.8 is sharper than pretty much every zoom lens (in my experience stopped down it's on par with the 70-200 f/4L IS, supposidly Canon's sharpest zoom) The 50mm f/1.8 II from f/4-f/8 outresolves or comes close to outresolving the sensor in my opinion and is pretty much the pinnacle of sharpness.

Do your results mirror these?
http://www.the-digital-picture.com …omp=0&FLIComp=0​&APIComp=4

Put your mouse over the images to see the 50mm crops and compare the two.

Yeah that green bleeding is what I meant by CA (chromatic abberation)

I think your lens is perfectly fine.

smorter wrote in post #5951897
A comparison with the 50mm f/1.8 II is too hard a benchmark for the 24-105 in my opinion. Even though it's cheap the 50mm f/1.8 is sharper than pretty much every zoom lens (in my experience stopped down it's on par with the 70-200 f/4L IS, supposidly Canon's sharpest zoom) The 50mm f/1.8 II from f/4-f/8 outresolves or comes close to outresolving the sensor in my opinion and is pretty much the pinnacle of sharpness.

Do your results mirror these?
http://www.the-digital-picture.com …omp=0&FLIComp=0​&APIComp=4

Put your mouse over the images to see the 50mm crops and compare the two.

Yeah that green bleeding is what I meant by CA (chromatic abberation)

WOW! That comparison tool is incredible! Thanks for the link man.

You know, yeah, my results do look like what that tool shows. Interesting. And even more interesting to me is that the 50mm f/1.8 II is even sharper than the f/1.4 and f/1.2 versions. I was actually going to go out and buy the f/1.2 to just show a comparison between high-end and "low"-end lenses... don't need to now. Saved me money!

Hmm, the jury is still out on the AF thing though... I got 1 vote for "perfectly fine." I still think I see the AF is out on my 24-105mm. If I get 2 more votes for being fine, I think I'll feel a lot better.

I'm not sure about the warranty rules in USA but I think you need the receipt/proof of purchase date to get it serviced. Maybe you can try and get the seller to send you a copy or something like that (not sure if it'll work though)

Determining whether AF is fine is quite difficult unfortunately. I try and take a photo of a flat object like a newspaper stuck on a white wall using AF (so nothing else can draw its focus), then another one of the same object using 10X Manual Focus and see which one is sharper (repeat a few times). I use the in camera LCD to determine this by zooming in to max in the image review then turning the main wheel back and forth to compare the two images in sharpness in the in focus area...if that makes sense. I'm not sure if my test is scientifically valid though..

I find the 3 battery test is not always the best because the AF locks on to the front or side of the battery randomly and it screws up the results a bit.