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Hi folks, i've bought a Sigma 24-70mm f2.8 HSM for over a month now and just thought i'd share my experience. Before i bought it, i searched the internet for reviews and found barely any! I'm sure people interested in getting this lens will have the same problem so i'll provide what experience i've had to help with that. The review that convinced me was a chinese review where they compared it to Nikon version and i saw very little difference @ f2.8. Quite frankly, i'm very surprised by the lack of buzz this lens has generated. Anyway, before i start i should mention i use D50 & D300, my lens line-up include: Nikon 28-200mm, 18-70mm, 50mm f1.4 and tokina 12-24mm. I'll be comparing the sigma to those.

Built
On the outside, the lens reminds me of the 18-70mm alot in terms of feel & looks. It is a giantly fat lens, make no mistake about that! The built is a step above the 18-70mm but a step below the tokina 12-24mm. The other thing is, the lens is very heavy, and i can't help but think a lens with this amount of weight should have a more solid built. It is a perfect fit on the D300. On D40 & D50 it gets very front heavy, and if you don't hold it by the lens, it feels like it'll break off from the body! I can't imagine this lens being used on a body smaller than D300.Take a look:





Design
The design isn't of a professional lens. It extends towards the long end, hence may suck in dust over time. However the zoom & focus rings are nicely damped & fluid in use. Unfortunately, it doesn't feature rubber sealing ring around the mount. The petal hood feels really cheap, much worse than tokina's petal-hood and it's actually smaller. Another thing that bothers the hell out of me is the 82mm filter thread. Being in NZ everything's expensive, the only 82mm UV filter my local shop had was NZ$125, so i opted for a stepping ring + 77mm filter instead. To my surprise, when i mounted this combination on FM2 film camera, the corners did NOT vignette! Not sure if FM2 has 100% view though...

AF
One thing you'll notice is the AF pathway is very very short, in fact you can see the entire pathway in the AF window. While this allows fast AF, but i think this may be responsible for the AF problem (that and sigma's QC). Mine has a severe front-focus problem at close distance focus. The dealer tested 3 copies for me all with the same results. D300's AF fine-tune adjustment does help but not at the closest distance (0.38m). This is a serious warning to all potential buyers.



Optic Performance
Now i'm sure this the bit you are all interested in. You can relax, it is easily the best performing lens in my line-up (though that's not hard). It is sharp at all apertures. My benchmark has always been 50mm @f4, and the sigma rivals that at all but f2.8. At f2.8 it's about the same as f2.2-2.5 on the 50mm, nothing a little software sharpening can't handle. Above f2.8, everything's so sharp that the prints will give you papercuts! There's also no evidence of vignette except at f2.8 on 24mm, even then it's not very obvious at all. There's also no issue of colour casts, in fact i can't tell the difference between the sigma and the rest of my nikon lenses. Surprisingly, i've yet to seen any CA visible, but then again i haven't been using it that long. Overall, there's no major weakness that's worth worrying about. It is the only lens in my kit where i don't have to stop down for image quality. Keep in mind the findings only apply to DX format. Feel free to ask questions about this lens.

Time for some 100% crops (none with UV filter of course!), all on D300 RAW straight conversion with NX2:

1. 70mm f2.8 ISO 3200 this one converted with ACR*


100% 1m from subject, focus problem is clear here


*2. 70mm f2.8 ISO 3200*


100%: No AF problem here!


*3. 24mm f2.8 ISO 200*


100%: Center


100%: Right


*4. 44mm f9 ISO 200*


100%: Upper right corner. No CA!


*5. 70mm f13 ISO 200*


100%: Center


*6. 70mm f10 ISO 200*


100%: Center


*1. 24mm f2.8*


100%: Again, focus problem visible here, i AFed for the center of the basket


*2. 24mm f2.8*


100%


*3. 70mm f2.8


100%


*4. 24mm f2.8 As you'd expect, sharpness decreases with close distance focus


100%

thank you for your very detailed review.
Sigma really need to do some work on their QC department and improve their AF accuracy.
they have many good lenses in their current line up like the
24-70 HSM, 50 f/1.4, 30 f/1.4
but their QC and AF accuracy is really letting them down...

Thanks for sharing this with us jeffery, and i've fixed the links.
you need to add the [ img ] and [ /img ] tags (remove the space) to your picture to get them display properly here.

hi, thank you Mr Admin. Yes, i managed to figure out the code from editing so thanks very much.

I checked out a number of other Sigma lenses after i bought the 24-70. I noticed quite a number of them have short AF travel path too, some of them HSM as well. I don't understand why have short pathway when HSM is as fast as nikon's SWM, it makes MF that much harder.

Thank you for the review.
re the lens focus ring travel distance...i'm not a lens engineer, but i think it's just a trade off between speed and MF friendly:

A smaller angle travel (higher internal gear ratio?) like your Sigma means faster AF but not so MF friendly.
A higher angle travel (lower internal gear ratio?) like a lot of Nikons means slower AF but more MF friendly.

Compare the latest Sigma 50mm f/1.4 with the nikon 50mm f/1.4 G....
Sigma's focus ring travel is approx 90 degree from infinity to closest focus distance
Nikon's focus ring travel is a bit more 180 degree.

Sigma's autofocus is A LOT faster than Nikon.
but Nikon's 50mm is definitely a lot more MF friendly.

Another thing i noticed is that most of the larger aperture prime lenses f/1.4 f/1.2 normally has a much slower AF speed than their their cheaper version (normally f/1.8).

e.g. Nikon 50mm f/1.4 G vs f/1.8D, Nikon 85 mm f/1.4D vs f/1.8D, Canon 85mm f/1.2 vs f/1.8...etc
i'm wondering if it has something to do with the shallow dof/higher precision AF required for these lenses?

I think what Yellow15 has said is true.

I think the faster the lens, the shallower the dof and hence the need for more accurate a/f. At F1.4, the need for precise A/f is much higher than fast a/f. Just my opinion!

Thanks for the review.

Hi yellow15, you mentioned the Sigma 50 has faster AF than the Nikon version. Do you have both? If so, does the slower AF on Nikon actually bother you? I don't actually find lens with longer AF path more of a bother in actual use. Sure they are slower, but only when going from one end to the other, other times you don't even notice it.

What i'm wondering is, why have a short AF pathway when HSM is already fast? The increase in speed compared to say AF-S 18-70 is hardly noticeable, but the (in)ability to MF is very.

I don't have both (crazy if i have both hehe). i only have the Nikon 50mm f/1.4G. (and i had the 50mm f/1.8D before)

I was really intereted in the Sigma 50mm 1.4, so i went to the local shop, ordered one ... but finally decided to buy the Nikon instead after trying both side by side, you can read my comments/impressions here: http://www.nikonjin.com/forum/showthread.php?tid=53

Anyway, both lenses use HSM/SWM motor design, with similar spec/price... but the Nikon 50mm f/1.4G's AF is A LOT slower than the Sigma 50mm 1.4, probably because of it's longer focus ring travel range (more optimized for MF).
Does the slow AF speed bother me?
Not when i'm shooting landscape/formal portrait..etc
But Yes it does if i want to shoot moving objects or when i want to take a picture quickly. i've missed many shots because the AF just took a little bit too long to lock the target.

So my guess is, if they make the 24-70 to have more focus ring travel for easier MF... it would significanlty decrease the AF speed, just like the 50mm 1.4G..

And i'm guessing the majority of the Sigma 24-70 users don't or rarely use MF, so it kind of make sense to optimze the lens for a faster AF speed than ablitly to MF.