Camera Labs

To play Devil's advocate, how did you come to the conclusion that you had to go for that specific lens?

There's the 15-85mm IS USM, which offers vastly better quality than the 18-55mm IS and it's priced roughly half way between it and the 17-55mm IS USM. No it's not quite as sharp but if you're willing to compromise quality a little bit if you can bring the price down noticeably, I reckon it's worth a look.

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Bodies: Canon EOS 550D w/ Magic Lantern
Lenses: Tokina AT-X 116 Pro DX f/2.8, Canon EF-S 15-85mm f/3.5-5.6 IS USM, Canon EF-S 18-55mm f/3.5-5.6 IS, Canon EF 50mm f/1.8 II, Canon EF 70-300mm f/4-5.6 IS USM
Accessories: YongNuo Speedlite YN-468 Flash, Neewer Macro LED Ring Light, Meike Battery Grip, YongNuo RF-602 Wireless Flash Trigger & Receiver YongNuo WR-128 Wireless Remote Control

The choice between the 15-85 and 17-55 is largely not down to price. The 15-85, which I picked, has the widest angle without going to an ultra-wide zoom. The 17-55 of course offers f/2.8 if aperture is a bigger priority.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.

Not to be awkward but actually, yes, the choice was down to price for me. I like the 17-55's sharpness but I didn't need that or its constant f/2.8 aperture enough to spend the premium. The 15-85 offered the best compromise to me - the wider focal range was a bonus.

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Bodies: Canon EOS 550D w/ Magic Lantern
Lenses: Tokina AT-X 116 Pro DX f/2.8, Canon EF-S 15-85mm f/3.5-5.6 IS USM, Canon EF-S 18-55mm f/3.5-5.6 IS, Canon EF 50mm f/1.8 II, Canon EF 70-300mm f/4-5.6 IS USM
Accessories: YongNuo Speedlite YN-468 Flash, Neewer Macro LED Ring Light, Meike Battery Grip, YongNuo RF-602 Wireless Flash Trigger & Receiver YongNuo WR-128 Wireless Remote Control

I never saw the 17-55 as having a noticeable sharpness benefit. That only leaves price and aperture, and I think for most, the aperture is the decider with price being incidental.

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Canon DSLRs: 7D, 5D2, 1D, 600D, 450D full spectrum, 300D IR mod
Lenses: EF 35/2, 50/1.8, 85/1.8, 135/2+SF, 28-80 V, 70-300L, 100-400L, TS-E 24/3.5L, MP-E 65, EF-S 15-85 IS
3rd party: Zeiss 2/50 makro, Samyang 8mm fisheye, Sigma 150 macro, 120-300 f/2.8 OS, Celestron 1325/13
Tinies: Sony HX9V.