Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- User Rating: 
Summary for Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- Ok for the price, but not for professional printing
Notes on Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- I purchased the Sigma 18-200 for use with a Canon Xt because I needed a wide zoom range and was on a tight budget. For the price this lens is OK. The auto-focus is slower than I anticipated, despite the reviews that say so. The lock on the one I purchased seemed stuck and the barrel kept coming out on it's own while walking. The first pictures I took with it were a great disappointment. I recently started a small pet photography business and also work for a local paper as their sport's photographer. I use a Sigma 70-200 2.8 for sports and it works great at an affordable price. As soon as I uploaded the test shots of the Sigma 18-200 I realized that despite my ISO being at 200, there was unbelievable grain (shot in daylight) as well as an overall muddy look to my pictures. It may have just been my lens. I tested it out against the kit lens (18-55) and the nifty fifty (50mm 1.8) and the Sigma was the worst in quality. I print pictures for my clients and I could not imagine sending a shot of such bad quality to print. Like I said, it may have just been the one I received, but the quality was just not good. I returned it and got the Tamron 28-75 2.8 for a couple of bucks more and could not be happier with it.
Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- User Rating: Summary for Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- Great All Around General Purpose Lens
Notes on Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- This lens provides adequate telephoto and a nice wide angle in one package. I've used it on both the Canon XT and XSi and it works great. It is the one lens I just leave on.
Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- User Rating: Summary for Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- An OK lens for the price; autofocus is hit and miss - and noisy.
Notes on Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- I received one of these for Christmas...so I've had it for 6 months now. I've taken thousands of shots with it, on both a Canon Digital Rebel XT (350d) and a Canon EOS 20d.
The bottom line...I like the lens - but the focus is not that great. Abour 35% of your shots are blurry due to inaccurate auto-focus.
Specifics...
1) At 200MM (Max telephoto), you will see some blur if you don't use a high shutter speed and hold it steady. This means that just placing your camera on the green "point and shoot" mode, or even "P" mode may not give you a fast enough shutter speed to keep from having blur unless you are in bright daylight. So....here's my technique: at 200MM you may want to bump up your ISO (film) speed to 400 or 800, then use Tv mode (Canon settings I'm talking about - manual shutter speed control) to get a fast shutter speed. I also hold the end of the lens (the petal filter) with my left hand and lean against a solid object or have a good foot stance - or use a tripod. All of this is not any sort of lens defect; rather, it is typical of using a long tele lens that does not have Image Stabilization (IS). You can get IS from Canon, but be ready to lay down some $$$ and carry multiple lenses...more on that later.
2) Noisy autofocus. Yeah, true, it is louder than other lenses, but so what. It is not any louder than the fake autowinder sound my Rebel XT makes. I find its focus quick and only sometimes accurate - except in low light. Although, I will say my 20d does much better than my 350d did with this lens in low light. But, honestly, I don't think the low light autofocus is any worse than the Canon 18-55 kit lens I initially ised. It hunted a lot too in low light, and often would not lock - necessitating manual focus. The manual focus on the Sigma works great in low light, or, to keep autofocus, you can use an external flash for IR focus assist and it locks right up - but it is not always accurate.
Other than the Tamron, you WILL NOT find as versatile a lens as this one, especially at this price point. Optical quality is great on my lens. You can do better - but with two lenses. My solution to have this kind of range if $$$ was no object would be the Canon EF-S 17-85MM f4-5.6 IS USM and the Canon EF 70-300mm f/4.5-5.6 DO IS USM...this would add image stabilization and 100MMs more range, but at much more cost, and you would have to carry two lenses.
I specifically bought this lens to have a compact, one lens solution. If you read all the reviews you can find, the general consensus is that the Sigma is better than the Tamron 18-200. Plus, the end barrel does not rotate, so you can use a circular polarizer. Show me a lens that has better bang for the buck in a one lens solution, and I'll buy it.
Update: I got sick of the blur with the Sigma. The focus is just not reliable enough. I bit the bullet and bought a Canon 28-70 F2.8L USM. Yeah, it is moe than double the cost of this lens and it is huge and weighs a ton, but the quality of the image is unbelievable.
Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- User Rating: Summary for Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- Great all purpose walkabout lens but could use image Stabilizer.
Notes on Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- I bought this lens for its compactness and light weight and nothing can beat that its amazing how compact and light it is. The range of 18-200mm is very useful and covered almost all my needs. The image quality is great and its truly an all around lens. At the full range of 200mm an image stabilizer can help. Overall this is a great lens its inexpensive and it is very recommended to cover a range used by 95% of the people from portraits to nature and wild life photography.
If you can spend more opt for the more advanced lens with image stabilizer this will be your final lens you will need nothing more......
Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- User Rating: Summary for Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- This Lens Rocks!
Notes on Sigma 18-200mm f/3.5-6.3 DC Lens for Canon ...- I've been using this lens with my Canon 20D for 3-4 months now, and I think I've taken it off only once or twice in that time. I love it. Its focal length range makes it incredibly versatile, and it's tack sharp through most of the range. Not as much distortion as I would expect at the 18mm end, and (as long as I keep a fast enough shutter speed and/or stabilize the camera) very crisp at the 200mm end. Best of all, when you're zoomed all the way out, you can actually get pretty close to a subject (within a foot or so) and still get a focus. Most longish lenses won't let you get anywhere near that close.
Another bonus with this lens: the seal with the camera is much tighter than with any of my Canon lenses -- so way less sensor dust!
It's my all-time favorite lens.:)
