Sigma 18-50mm F2.8 EX DC

I bought this lens because I've seen many good reviews and very good pictures taken with it. I also saw some bad reviews, but I thought I can't be that unlucky to get a bad copy.
Well, I was that unlucky. It had bad front-focus, it was extremely soft on the top-right corner too and even from day one I noticed some dust particles inside it.
Fortunately the shop that sold it to me (online shop) is replacing it with a Canon 17-40 L F4 and I am paying the difference. I'm not willing to go over several lenses just to find a good copy, so I'm betting on Canon L glass this time.

All in all, this isn't a lens you want to order online. Be sure you test it before paying for it, or check the return policy of the shop.

- F2.8, but if you aren't lucky enough to get a good one, it will be soft at 2.8
- good focal range
- relatively small and easy for- macro, even if it isn't true macro (1:1). It's just 1:3 magnification.
- polarizing filter can be used since focusing doesn't rotate the front element
- the build is pretty good, it feels solid; the zoom ring feel comfortable in using too; the finish gives it a classier look
- even with all the problems I mentioned, at smaller apertures it produced good images; for as long as the subject was in DOF it worked pretty well

- Sigma has bad QC, especially with this model it seems (heard other users complaining about it)
- bad front-focus
- top-right corner very soft
- AF behaves erratically especially in low light, but it might be because the above problems
- AF isn't HSM, thus it's a bit noisier and slower
- Focus ring moves while using AF
- Focus ring has a very small rotation angle, making it impossible to use Manuel focus
- if you want manual focus, you need to switch to it

Canon 18-55mm F3.5-5.6 (Canon 400D kit lens)

Extremely bad service in Romania: there is a dealer but they won't help you unless you bought the lens from them; International Warranty has no meaning here it seems.

I promised myself I wouldn't buy anything big at the Camera show, man did I break that one. I was wandering around the show and happened to stop by the Sigma demonstration booth, a couple friends had purchased Sigma products before and both seemed happy about it. Using my Nikon D70s I started trying out lens, and a sales rep came over to me and suggested I try this latest offering that they had. I slapped on the lens and took it over to where a model was standing to give it a shot. Man I couldn't be happier. I walked right over to the Henry's table and bought one.

I have since used it in the two primary fields I shoot in, events, and architecture. It performed admirably in both. If you're looking for a replacement for a kit lens, this is it. It gives you a fast lens (f/2.8) at a price under $1,000. It's a fast sharp lens, plus has good Macro capabilities as well.

Anyone with a dSLR, still using just a kit lens, should get this one to replace it, hands down. (Comes in multiple mounts Canon, Pentax, Sony, Nikon). The money you save can be put towards a 50mm f/1.8.

- Sharp, razor sharp
- Fast lens
- Good Price

- Slow on Auto focus
- AF motor Noise
- only zooms to 50mm

Nikon Nikkor AF-S DX 18-70mm (Kit)

None required

I have the Nikon D70 camera and most frequently use the Nikon 18-70mm lens. While I've been pretty happy with this lens, I've often wondered if there wasn't something a little shaper and a little faster out there in a price range that I could afford. After reading several highly positive reviews of the Sigma 18-50 I decided that this was the lens for me.
To tell you how impressed I am with this lens, after shooting a "test roll" and carefully viewing the pictures in Aperture, I'm putting my 18-70 on Ebay and getting rid of it.
This lens delivers everything it promises. It's incredibly sharp, focuses just as fast as the 18-70, and I'm also amazed at how small the minimum focusing distance is.
Yeah, if you shoot at a brick wall at the 18mm end the distortion is significant, but nothing that can't be fixed with the latest software.

Sharpness!!! WOW. I can't overstate this enough. This lens is really sharp.
Contrast - nice and punchy.
Ability to open up to f2.8.
Fast focusing.

Focusing noise is slightly louder than the Nikon 18-70.
Distortion at 18mm.

Nikon 18-70mm AFS

I purchased the Sigma 18-50mm f/2.8 EX DC to go with my Nikon D50. Essentially, the constant f/2.8 aperture is what did it for me. Even Nikon's and Canon's midrange zooms usually have f/3.5-4.5. I wanted f.2.8 for the extra low-light shooting ability and the added depth of field flexibility, and I wanted it without paying $1200 and carrying a lens that weighs in at 3 or 4 lbs. This lens fits the bill pretty well. Overall, performance is good. The AF is not a silent, HSM motor, but for normal focusing the noise is not distracting. It's quick enough unless focusing from macro distances to long distance. When doing that, it takes the lens a bit to go from one end of focus to the other. Overall, though, the AF is fast and doesn't hunt too often. A weekend before buying this lens, I played with my friend's Canon L lenses. (He's a pro wedding shooter.) When I got this lens, I was pretty thrilled to find AF speed close to his lenses. Also, I didn't feel like my lens hunted more than his did in low light. So, yeah, that was encouraging. In terms of sharpness, I'm happy with the lens. Even at wide open f2.8, I find the lens is quite sharp. In the bottom-right corner of my lens, it gets a bit blurry, but in real life shooting, I never notice. It's maybe 1% of the total picture area. As for distortion, there is a bit if you're shooting straight lines along the bottom of the photo, but I use PTLens to solve this quite well. Vignetting is also present when at 18mm at f/2.8, but overall, I haven't found it to be noticeable in normal shooting conditions either. Again, PTLens can help with this when it is a problem. As for chromatic aberations, I was very pleased that this was not an issue at all. I've shot fairly demanding shots in this regard and never seen any fringing. So, in this regard, I'm 100% satisfied.
In re-reading my review, I think I come off a bit too negative. I like this lens. In fact, I really like this lens. It's sharp, has reasonably good AF, isn't too noisy, and has a wonderful constant aperture that can't be found on 1st party lenses for less than $1000. I paid about 1/3 of the price of the Nikon 17-55mm, and I also have a smaller, more convenient lens. Do I wish there was absolutely no vignetting or distortion at 18mm? Sure, but these issues are not really noticeable in 90% of my shooting. So, overall, and especially for the money, I really like this lens.

-constant f/2.8 aperture is really nice
-sharp
-quick AF
-at 50mm, distortion is very mild

-mild barrel distortion at 18mm
-some vignetting
-fairly quiet, but not HSM

-wide range of Canon lenses, but not extensively, so not much.

-haven't needed it yet

I plunged for this because I wanted constant aperture throughout the zoom range, faster speed, and the extra 10mm over the Canon 17-40L. And of course, the price. I'm very impressed by the lens. Seriously sharp. I've sort of experienced focusing "problem" mentioned by many reviewers - but I'm not sure if it's really the camera instead of the lens. It crops up when one is trying to focus on really thin foreground/background objects, so my guess is perhaps the actual autofocus point selected by the camera was wrong - and that is because the user is not aiming perfectly. In any case, simply using manual focus solves everything. However, one possible "problem" is that depth of field tends to be quite short especially in low light, so if you didn't focus on the right thing, the result could go very wrong - but that's par for the course for any lens. Build quality is great and solid - material feels like magnesium alloy but I'm not really sure. Also, it's not too big (an inch longer at widest than the 18-55mm kit lens on the 350D at full tele) and not too heavy.

- build quality - constant aperture - price - size

- narrow depth of field (?) - front of lens element does not rotate during focus, but a section in the centre does. Slightly annoying if your hand happens to be in the way