Lenses

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Optical quality
Value for money
Overall

Cons: Vignetting No constant Aperture

Pros: Good image Quality

Summary: My favorite All-round Lens!

Build quality
Optical quality
Value for money
Overall

Cons: Field curvature at wide angle. Slight CA.

Pros: Sharp. Very sharp stopped down a bit. OS works. A little faster than most others. AF reasonably fast.

Summary: Good choice for all around lens.

Build quality
Optical quality
Value for money
Overall

Cons: - No full time manual autofocus - Focus ring turns only 60° or so, difficult to focus manually - (Suspect) production quality issues, many people report front/back focusing

Pros: - Excellent image quality (stopped down), good quality even wide open till 50mm - Good and fast autofocus (comparable to Canon's USM) - Good IS (again comparable to Canon's) - Decent build quality, no zoom creep (and lock switch provided, unlike Canon) - Fast for a zoom with this focal range - Not macro but VERY close focusing - Cheap, and hood included (shame on you Canon!)

Summary: I don't understand the bad user reviews lamenting softness.. in the range 17-35mm this lens is super sharp, and for the rest is still very sharp if stopped down 1 stop. So the softness problems some people is experiencing must be front/back focus i guess.. something they should ask Sigma to fix. Before buying this lens i compared it side by side (shooting resolution charts) with the highly regarded Canon 15-85mm, my old Canon 17-85 and Canon 50mm prime which is also super sharp. The Sigma matched or slightly exceeded (short range) the Canon 15-85mm AT THE SAME APERTURE at all focal ranges, it doesn't make sense to compare the two lenses always wide open because the Sigma is one stop faster at all focal lengths. Wide open at long focal lengths it is indeed a bit soft, but a soft F4 is still better than no F4 (and it improves a lot already 1/3 or 2/3 stopped down). As for Chromatic Aberration, it's present only at the shortest focal length, but the same is true for the Canon 15-85; if you want to see a lens with CA problems, look at the Canon 17-85 which is plagued in the whole focal range (and it's softer than the Sigma too). This lens has L-class image quality (if you get a properly calibrated auto focus) at a bargain price!

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Optical quality
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Cons: Chromatic aberration = huge problem. Some flare problem.

Pros: Cheap all-round lens. quick and correct auto focus. Good optical stabilization.

Summary: Shoot 900 images indoor, narrow space. 400 images @17mm. All need to apply lens correction filter in CS.

Build quality
Optical quality
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Overall

Cons: Very warm colors comparing to standard Canon 18-55 IS. Heavy. Slow focusing in low light. Soft Picture quality. Visible distortion.

Pros: Macro

Summary: Was expecting better quality of the pictures.

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Cons: Slightly soft picture what doesn't fortunately come as obvious with 6Mpix sensor (Nikon D70) what it would be on 12Mpix or so on. Manual focusing ring is little narrow on its turning range, so getting it sharp takes steady hand. What really annoys is the the zoom what rotates wrong direction for me. This is of course individual broblem, but it seems after month still difficult to fit it back of my head...

Pros: Tracs focus very fast and accurate (backfocus IS fixed from the body). Can't get from stabilization quite that 3 EV improvement what promised. Surely 1 to 2 EV advantage on real situations has come apparent. Light passes trough nicely on wide end - would be great lens if that happened on another end too. Guess that would cause more softening on images and other optical difficulties.... For me the macro is really positive surprise! It focuses really close on 70mm end. Haven't measured but somewhere close as 2 cm. On smaller aperture it really gives nice details and works fluently! OS doesn't seem to shorten battery life noticeably what is really nice thing to discover!

Summary: Nice piece for lower resolution sensor. Not too much to complain about this other than price... Anyhow, I am pleased on this lens. I was looking one lens to rule all sitatuations and this is it for me. I can spot the possible faults on optical quality on this if you want to go really pro... softening and all. But this is not too big of a compromise to get good photos with one lense. I'm planning to keep this!

Build quality
Optical quality
Value for money
Overall

Cons: -White markings on the lens can be scratch off easily. Mine got scratched off just by thumb nail while changing AF to MF. -Heavy even on my Canon 50D -Backfocusing problem for mine -Not accruate focusing in low light, slight hunting occur. -Colour too warm compared to my Canon lens. -Very soft picture quality after 50mm. -Soft picture quality when wide opened. -distortion quite visible at 17mm -Macro focal length too far to be considered as a Macro lens

Pros: -Good Focal length and aperture range. -Fast and silent auto focus. -Very good center picture quality -Little chromatic aberration -OS and Macro

Summary: Overall a very good all round lens in the market. if it didn't backfocal on my 50D i would have given it a better score.