Canon 17-40 and Sigma 17-70 comparison

[Citizensmith]

I own a 17-40 (on a 300D). I like it, its a solid lens as you'd expect from an L. My only problem is the 40 part as I sometimes find that short for a walkaround lens.

At work I just got a 17-70 (on a 400D). I'm still getting used to it, but as it is something I'd considered I figured I'd run a few comparisons.

First, the stuff you can't take photos of.

Autofocus.
The 17-40 is silent and deadly. It finds focus quickly and makes no fuss about it. The Canon has full time manual focus.
The 17-70 is fairly quiet and pretty quick. It's still good, definitely good enough, just not the same as the 17-40.
17-40 1: 17-70 0

Price.
The 17-70 is a lot cheaper. Both come with hoods but the Canon hood is for full frame. Small sensor users may consider getting a different hood for the 17-40.
17-40 1: 17-70 1

Build.
The 17-70 is smaller which I would consider a good thing, but it really doesn't have the build of the 17-40. Both have a non-rotating front, but the Sigma extends, while the Canon does not. The Sigma feels solid, but the zoom ring is overly tight and mounting the lens on the camera seems to need more of a twist than any other lens I've used. I'll call this one a draw, better build vs smaller size, as the Sigma still has good build and the Canon isn't huge.
17-40 2: 17-70 2

[Citizensmith]

Close Focus.
This was a clear win for the Sigma. While the photos don't look that different the Canon was at its limit. The Sigma would have gone close if I'd taken the hood off.
The Canon image is first.
One other notable difference is a slight warm cast to the sigma. Or a blue cast to the Canon. Hard to tell, but I'd say the Sigma shot looks warm.
17-40 2: 17-70 3

[Citizensmith]

General detail.
This next shot was to look at General detail. In reality this should be a whole slew of tests but I have neither the time or the skill to do it accurately. In these two shots its pretty much a wash, with the Sigma again having a warm look.
Again, Canon first.
17-40 2: 17-70 3

[Citizensmith]

Corner sharpness.
From the last image we have a crop from the bottom left corner. The Sigma while good is a little softer and shows some haze and color fringing the is absent from the Canon image.
17-40 3: 17-70 3

[Citizensmith]

Aperture - Maximum
The Sigma is an f/2.8-4. The Canon is an f/4.
While the Sigma gets up in maximum fairly fast it still have a definite advantage.
17-40 3: 17-70 4

Aperture - Using the lens wide open at 17mm.
Just a small image for this as it shows very little.
Wide open (f/4) the Canon showed no notable vignetting.
Wide open (f/2.8 ) the Sigma showed very slight vignetting. Nothing concerning and fairly hard to see, but it was there.
A draw because the vignetting on the Sigma was too insignificant to hold against it.
17-40 4: 17-70 5

[Citizensmith]

Zoom Range.
The Sigma has the whole 40-70 (64-112) range on it that the Canon doesn't.
17-40 4: 17-70 6

Distortion.
Both seem about the same, and wide open neither are great. Of course you can't expect miracles from a wide angle.
17-40 5: 17-70 7

[Citizensmith]

Flares.
Both lenses have well controlled lens flare. The Sigma had some slight flare, notable principally in the opposite corner to the sun. Moving the sun just out of frame had little effect on the flare, just changing its shape. The Canon had flare with the sun just outside the frame, although marginally better controlled than the Sigma. Surprisingly there was no visible flare from the Canon with the sun in the shot. Point to the Canon.
FWIW neither lens had a filter on for these shots.
17-40 6: 17-70 7

[Citizensmith]

How wide can you go.
Not much in it, not really enough to make it worth a point, but the Sigma (second image) is definitely wider.
17-40 7: 17-70 8

[Citizensmith]

Sharpness.
Lastly some overall shots. Please note that the sigma image is incorrect. The wide part was f/2.8 not f/4 as noted.
The Canon is very good. Sharp wide open so f/8 doesn't make enough difference to consider important.
The Sigma is good. On 100% crop its fairly soft wide open but that is gone by f/8.
At f/8 there was nothing between them. However I'm going to give the point to Canon for wide open performance. I know that sounds unfair as the Sigma was at 2.8, but if you've got it you better be able to use it, and the Canon had the Sigma beat at f/4.
17-40 8: 17-70 8

Color and Contrast.
To be honest I really couldn't see much difference. Both were very good on the wide shots. The Sigma did seem to have that slight warm cast, but it was only notable on white surface. Draw.
17-40 9: 17-70 9

[Citizensmith]

And the final scores. Equal. Ah well.

Take your pick. The Canon is more expensive but you get your moneys worth. The Sigma has better range, but where they overlap the Canon does it better. It's all a wash really. Anyone want to send me a 17-55 and 17-85 so I can check them out too.

And, to be honest, I think I was hoping the Sigma would win. I really do find the 17-40 range too limiting and wouldn't mind an excuse to swap to something else. This was me seeing if the 17-70 would be a good choice. It's a nice lens as its reviews had implied, but offers no overall benefit vs the 17-40. My other solution (Keep the 17-40 and add a 5D and 24-105) is a little expensive.

Oh, and as someone is bound to make the point. Yes, I know the 17-40 is a full frame lens and the 17-70 isn't. This review was done on a 400D and so reflects just the results a small frame sensor user could expect.

[El Duderino]

Thanks a lot for putting this together.

[KevNJ]

Very nice write up, thats for the time put into it. Was a good read.

[grinchy]

good job on this article..

[Tony-S]

I sold my 17-40L for the 17-70. It was a bit soft wide open, but sharpened up nicely at f/5.6. It's saturation was remarkable - certainly better than the Sigma. Had I planned to migrate to a full-frame camera one day, I would have kept it. It is, afterall, designed for such cameras.

[kennys350d]

My cousin has the 17-40L, and I was tempted to buy it as my first L lens, but the Sigma was to hard to refuse, so I went w/Sigma.