Canon 17-55 2.8 issues. me or the lens?

[gbc]

Just got this lens refurbished. Some shots, like the cat below, look pretty sharp. Others, do not. So I'm wondering if it's the lens or if it's just me. I'm wondering if the autofocus is faulty. Don't have any previous experience with this lens, so any opinions would help. Thanks.


All shot on a rebel xsi.


f 2.8, 1/1600, 55mm, ISO 200


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Maybe this is a light issue, but I couldn't get this sharp. Maybe the autofocus couldn't lock on?


f 6.3, 1/250, ISO 200


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This one looks better, I think. I'm just not sure why some are really crisp and others are not.


f 2.8, 1/50, 55mm, ISO 800


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[Benjamin]

Can't tell if it's a focusing issue in the first two photos. But as long as the lens is able to deliver sharp images in some of the photos, the lens sharpness should not have problem. You can run through a focusing test to see if the camera is front/back focusing (I assume that you know how).


Also, try to test sharpness in good lighting, not just because good lighting will yield fast shutter speed, things do appear better in sharpness in good lighting overall. Always use a tripod and shoot stand still subjects for such a purpose - in your case your body may have moved back and forth slightly without noticing (I do the same) or the flower may shake so they're slightly off focus when you take the shot due to the wind.


Just my $0.02.

[bradlove]

The 17-55 is not a macro lens and because of that you might have been trying to focus too closely on the first picture and that is why it is out of focus. The other two pictures look great and are representative of what this lens is capable of when used correctly. Hopefully you were just trying to focus too closely and there is nothing wrong with your lens.

[Colin]

it looks like all of them are sharp. It may be that when you get closer, the depth of field gets smaller, and more is out of focus, but that's just because the focal plane is 'thinner' in a sense, shallower depth of field. If ANYTHING in the picture is sharp (like some of the flower is, and most of it is not), thenthe lens is sharp. If you want more to be sharp, you need to simply stop down and use a smaller aperture setting.


If the part that is in focus isn't the part that the autofocus point is set to, that's an entirely different problem. I had that problem with a 135mm that I sent back, but now that store can't get them anymore. With that issue, the lens focuses to the wrong distance. I.e., you focus on somebody's eye, and the tip of their nose is in focus, but the eye isn't. you can test this with a ruler, taking a picture at an angle. Offset it, say 30-45 degrees from flat (flat being perpendicular to the direction of the lens direction), and use a single autofocus point set at a point. Then check to see if that point is in focus. If it is, you're good. If it isn't, but some part of the ruler, either closer or farther way from the focus point is, then it's back or front focusing, which needs to be fixed. As some have pointed out, if you can't do calibrations with your camera, you may want to send the lens in with your body so that the lens is calibrated to match the camera, as it may actually be the camera body, or just the combination of them together, that's the problem.


However, it looks like it's entirely possible that it's just a matter of a narrow depth of field up close. Just stop down, of course you might have to crank up the ISO or exposure time to compensate, but that's the headache/fun part. []

[gbc]

Hey, thanks for the tips. I will definitely try that out. I guess I've been lucky so far, having never gotten a bum lens. I hope this isn't the case this time. I think maybe I was too close, or the wind kicked up. But thanks again!