better IQ?

For a crop, which has better all around IQ please rank

-Canon 15-85mm f/3.5-5.6 IS
-17-55mm f/2.8 IS
-Tamron 17-50 non VC

I would rank the 15-85 and the 17-55 just about even as far as IQ and would choose between them based on needs, speed vs focal range. The Tamron would rank third in this comparison.

DanFrank wrote in post #14688426
For a crop, which has better all around IQ please rank

-Canon 15-85mm f/3.5-5.6 IS
-17-55mm f/2.8 IS
-Tamron 17-50 non VC

lots of opinions and judgement here on the better "IQ" (whatever that is !)
But it depends on the focal range, the minimum aperture (do you need f2.8 ?) and do you need "IS" image stabilization

look at lens review sites like
www.photozone.de
or
http://www.the-digital-picture.com …omp=0&FLIComp=0​&APIComp=0

If you look at the photozone website as previously suggested, you will see the Sigma 17-50mm 2.8 has better numbers than any of the 3 you have listed.

nightcat wrote in post #14688546
If you look at the photozone website as previously suggested, you will see the Sigma 17-50mm 2.8 has better numbers than any of the 3 you have listed.

but what are the better "numbers" ?

optical quality ratings?
MTF resolution numbers?
price/performance ratings?

IQ depends by far more on the user, rather than on the equipment.

But in my humble opinion, 17-55 2.8 IS would give the best IQ overall, since it has both fast aperture (nice background blur, less ISO required) and IS (improves sharpness).

17-55mm f/2.8 IS

of course .

ed

I kept my 15-85, sold the 17-55.

15-85 is meant to be sharper or at least as sharp as the 17-55, and isn't as prone to flare. IMO the canon isn't worth 3x the cost of the tamron, IQ is extremely close, though AF is faster and it has IS, but then the sigma is $400 less and has those two things.

watt100 wrote in post #14688672
but what are the better "numbers" ?

optical quality ratings?
MTF resolution numbers?
price/performance ratings?

The numbers on the Sigma I referred to are MTF (resolution) numbers. Photozone comments... "starting at f/4 it beats or at least matches alternative products including the more expensive Canon EF-S 17-55m f/2.8 USM IS. The lens is extremely sharp across the frame here with no obvious flaw across the zoom range."

Here's the review... http://www.photozone.d​e/canon-eos/531-sigma1750f28os

rick_reno wrote in post #14688750
I kept my 15-85, sold the 17-55.

Rick, I have the 15-85 and I'm wanting a zoom 2.8. Tell me why I shouldn't

For me it came down to full time manual on the 17-55, the Sigma doesn't have that.

Does the 15-85 use a micro motor or does it have ring USM? I think it still has full time manual using a clutch if it has a motor. I also wanted a faster lens for what I use the 17-55 for. IQ on the 15-85 is very, very good from what I have seen though. I haven't had any flaring issues with the 17-55, but I always use hoods.

Keyan wrote in post #14692046
For me it came down to full time manual on the 17-55, the Sigma doesn't have that.

Does the 15-85 use a micro motor or does it have ring USM? I think it still has full time manual using a clutch if it has a motor. I also wanted a faster lens for what I use the 17-55 for. IQ on the 15-85 is very, very good from what I have seen though. I haven't had any flaring issues with the 17-55, but I always use hoods.

It has ring USM and FTM.

The point of the 15-85 is a compact lens that has a wider wide and a longer long end than the faster lenses are capable of.

Funny thing to me is all 3 lenses are very different despite the similar focal lengths.
Tamron does not have USM/USD drive so focus is spotty in lower light and no VC
17-55 is 2.8 and IS and expensive
15-85 is wider and longer but slower and variable Ap

So sharpness is only one factor amongst quite a few to consider between these choices.