I just picked up an EF 24mm f/2.8 a few days ago. Taking a few test shots on my 40D, I've noticed a couple things, mainly that wide open (f/2.8) at close range (within a few meters) it mostly (but not always) front focuses -- the target is at the back of the in focus region. Stopped down even a little the focus seems to shift to the correct range, the more it's stopped down the less finicky it seems. The second thing is that the lens seems pretty soft unless it's stopped down considerably, say to f/8, where it starts to look like a completely different lens. (I may or may not put some expired film in my Elan 7NE and try it out there.)In reviews I read that focus can be a little tricky in this lens, I'm just wondering if this is within the norm and I'm just doing something wrong, or if I should try another copy. (This is my 4th Canon lens, and the first that hasn't been spot on in auto focus under similar conditions, so I don't think it's me . . .) I'm leaving on a trip in a little under 2 weeks, so I don't have time to send it in to Canon for calibration, I would either exchange it for another copy and hope for better results, or just work with it for now and send it to Canon when I get back.Links to a few example shots. In all cases the center phone is at 24" on the yardstick, and I'm focusing on the "Uniden" logo near the earpiece. The ratio in these pictures, of about 1/3 focus attempts being correct, is probably about right, maybe a little generous.Front Focus: Exposure: 0.002 sec (1/500) Aperture: f/2.8 Focal Length: 24 mm ISO Speed: 400 http://farm2.static.flickr.com/1073/1347777342_c5e0f737bc_o.jpgFront Focus Exposure: 0.002 sec (1/500) Aperture: f/2.8 Focal Length: 24 mm ISO Speed: 400 http://farm2.static.flickr.com/1059/1347779668_f64644aa53_o.jpgReasonable focus range Exposure: 0.002 sec (1/500) Aperture: f/2.8 Focal Length: 24 mm ISO Speed: 400 http://farm2.static.flickr.com/1206/1346892317_c1ecc816a7_o.jpgEdit: original post had the first and third photos swapped

Well, I can see what you are talking about... i.e. a front focus on the first two. If this is what you get 66% of the time, I would say that's not good, and not the norm.FWIW, I have a 24/2.8 which I use on a 30D, and do not experience what you are seeing. Your comment regarding stopping down working/sharpening up I interpret as a function of the DOF changing, and don't have any bearing on the AF. for that matter, AF is completed wide open, and then then the lens closes to the desired aperature prior to shutter opening.Too bad about your time limit as that does limit your options and finding out if it's a lens calibration, camera issue, or testing issue. FWIW, I assume you set the focusing on your camera to center focus sensor to eliminate any issues of the camera picking the wrong focus point.good luck, Dave

Thanks. I think you're right about f/8 and DOF, where it decides to focus at f/8 just matters a lot less. And just to confirm, I was using the center focus point (shooting in Av mode).After trying a few more shots, and re-reading reviews of the lens (none of which mention behavior consistent with I'm seeing) I decided to try and exchange. Reading reviews of this lens, I didn't expect it to be perfect, but I just can't get in focus shots at f/2.8 without manually focusing, so something must be wrong.

yeah, i'd do an exchange. i had this lens with a crop camera. it was very nice.. size/weight, focal length and fit on a 20d. always quite sharp. great for your type of photography.bcleewrote:Thanks. I think you're right about f/8 and DOF, where it decides to focus at f/8 just matters a lot less. And just to confirm, I was using the center focus point (shooting in Av mode).After trying a few more shots, and re-reading reviews of the lens (none of which mention behavior consistent with I'm seeing) I decided to try and exchange. Reading reviews of this lens, I didn't expect it to be perfect, but I just can't get in focus shots at f/2.8 without manually focusing, so something must be wrong.

I have this lens on a 20D and find the focus wide open at about six feet is not reliable. I do not shoot charts or carry yard sticks, but I know what I see is not what I want. If you stop down a bit, depth of field might obscure the issue, it works for me.

maybe you need to exchange yours, too?richardalanfoxwrote:I have this lens on a 20D and find the focus wide open at about six feet is not reliable. I do not shoot charts or carry yard sticks, but I know what I see is not what I want. If you stop down a bit, depth of field might obscure the issue, it works for me.

I use 24mm f2.8 with 10D body and the focus at 2.8 and short focusing distances is very precise. Try to exchange the lens for another copy if you don't like the results. Anyway, have a nice trip

Thanks everyone for your comments. To follow up, I just got my new copy today. At 2.8 the focus is a bit more jumpy than my other lenses (well, maye it competes with the 50mm f/1.4 at 1.4) but across 6 different targets and 20 shots, it got a perfect focus (center of focus just slightly behind the target, but the target in focus) 11/20 shots, and I would say acceptably close in more than 2/3rds of the shots. I marked down 7/20 as front focus, but 4 of those were on a single target which apparently the camera didn't like. So if I throw that target it's about 73% perfect focus, 93% acceptable focus. Again, this was all at f/2.8 -- wide open. That's a lot better than the > 67% front focus I was getting with the last copy, so I'm happy with this one.And to be clear, I don't usually do this kind of testing with a new lens -- I usually take a few shots in my back yard, including some shots of a dark pebble on the top of a concrete wall at an angle to see the DOF, just to check out the lens. With the first three lenses I got, they seemed to be performing perfectly so after that I just used them. This one (the first copy) I wasn't getting a single shot in focus at f/2.8, so I didn't start shooting pictures of rulers until I was trying to figure out what was wrong.

What dealer did you purchase from? Was there any problem exchanging it?

I had a 24/2.8 which was a dog. It did nicely on my EOS-3 but with my DSLR it just didn't cut it. The images looked as bad or worse than the dog-toy 18-55 kit lens. I just had to sell it away. The 17-40L that replaced the kit was way better.

trumpet_guywrote:What dealer did you purchase from? Was there any problem exchanging it?B&H, so I don't expect there will be any problems. My experience with B&H is that if they even suspect you might be unhappy for whatever reason they offer to let you return or exchange. Since they're closed until next week I had them ship a new one to me & charge my card (they don't cross ship replacements unless you offer to let them charge your card). I'll get a refund when they get the other one back.