Bought new lens ~ Need your opinion please

Just bought the Sigma 17-70mm for my 20D. Can you help me determine if this is a good copy or not? I'm a bit concerned about the softness from 2.8 to 11. I've read numerous statements it is indeed soft wide open but based on reviews (Photozone) and testamonials here it should be very sharp from F4 to F11.

All center crops, tripod used with timer, camera settings set to fine large jpeg, image parameters set to average (parameter 2) Is the mirror shake at 2.8 a big factor in softness? I'm thinking of returning it tomorrow but I would like to hear your opinions first. So what do you think? Am I being too critical?

2.8

Wide open looks a little soft, but they are cropped as well.

MikeI wrote in post #3140426
Wide open looks a little soft, but they are cropped as well.

Thanks Mikel. I did compare sample images from Photozone and my own. Full size images from Photozone is way sharper than mine even at same aperture values. Even closeups of grass are soft.

Your fastest shutter speed was 0.250 s (1/4), even on a tripod your going to get movement, seems no mirror lock up used... test it in the real world, somewhere bright...

looks about right for that type of lens, stopped down it's more than sharp enough

At shutter speeds like that, mirror slap can start to affect it - mirror slap does not change depending on aperture, as it's more akin to camera shake, rather than being misfocussed.

These shots don't look like they're affected by mirror slap - it just looks a bit soft wide open - sharpen a bit, and add some contrast, and you should be ok.

As Pete says, test the lens in an environment more akin to how you will use it in the real world.

Thats a big step in sharpness from f2.8 to f4. Frankly, I'd be disappointed with that performance wide open. I don't have that lens so I can't comment on how your's compares to a good copy. I would consider sending it in for calibration. The improvement will be worth the wait.

EDIT: Agree on the 1/4 exposure being way to slow for testing purposes, tripod mounted or not. Do another test in better light.

can i suggest something that may be totally wrong. i reckon its misfocusing, and as you focus on the box its actually focused slightly infront of the text, and hence why it gets sharper as you stop down (as the text enters the limits of acceptable sharpness) but not sharp as expected. probably needs calibrating, so you should get a test chart and see if it front/back focuses.

Thanks for all your inputs. My apologies for testing the lens the wrong way. I went back to the store today and got another copy. Here's a sample:

Cropped, default parameters, fine large, and the camera stabilized by my hand and the bench

Re focus test chart, what kind of chart is this and where can I get it? I saw it on some website but couldn't understand the language.

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