Bests & Worsts Reviews from Amazon

I've had mine for three weeks now and have taken several hundred pictures under a wide range of conditions. I read all the reviews here and on other sites, both for Canon and Nikon mounts before I made a purchase. I hope to compare and contrast my experiences with what I've read here and on other review sites. My camera body is a Canon XTi. I read some reviews that complained of chromatic aberration (CA). Yes, there is some at the edges, at some focal lengths and apertures. If you look at the test results ([...]) you will see that the lens performs excellently at around f-6.7 to f-8. Almost no CA and excellent sharpness. This lens simply wants to run best at about f-8. So, I've taken to using my camera in Av mode at f-8 when I'm using this lens. Excellent results with no visible CA. I read some reviews that complained of 'softness' of the images in some situations. This is attributable to two issues. One is that if you let the camera program mode choose an aperture, you may get a very high number. At very high-number apertures (f-16+) the lens is limited in sharpness, not by any design fault, but by a basic law of physics. It's near the diffraction limit for that aperture. The second issue is that at long focal lengths the adaptive multi-point auto-focus algorithms mess up. If you're not watching carefully they may focus on a bush that's 50 feet away leaving the landscape that you were trying to capture out of focus. Blame the camera and not the lens. What I've been doing is using spot focus at longer focal lengths. Focus lock on what is supposed to be in focus and then frame the scene. Do that, and run Av mode at f-8 so you don't get high f-numbers, and 'softness' will not be an issue. I've read some complaints of slowness or inconsistency of focus. This seems to come mainly from Nikon owners. For me, it focuses very quickly and quietly under all lighting situations. No problems at all. I've taken it out on a dark night and pointed it at a star and had focus lock within two seconds. I think the issue is more related to the focus algorithms running in the microprocessor in the camera body than to the lens itself. With my Canon XTi, I couldn't ask for better performance. I've read complaints of 'lens creep'. That's the tendency of long-focal-length lenses to extend to their maximum focal length when hanging down, due to the weight of the front elements of the lens. Mine doesn't do it, yet. This could develop in the future. I don't expect it to be an issue, though. There's a simple lug that can lock the lens at the short focal length for carrying. While shooting I tend to support the weight of the camera and lens with my hand on the lens, and use the other hand on the body to work the controls and point. So lens 'lens creep' would not be an issue. I've read some complaints of inconsistent force on the zoom ring required to zoom through the entire range. That's true. It does take a bit more force to zoom between the 70mm to about 120mm range. It's noticeable, and I wish it wasn't there, but I know why that is. Somewhere about 70mm the cams in the zoom mechanism go into a range where large amounts of extension occur with small zoom ring movement. While it's not desirable, it's also not at all a problem. This lens is heavy, especially if you're used to the kit 18-55 lens. You'll get used to it and you'll be delighted if you're a Canon owner. If you're a Nikon owner you may have issues with focus in low light. All-in-all I'm quite happy with the purchase and I don't hesitate to recommend this lens. But, to be really happy with it, you have to understand the compromises that are part of its design and how to work around them. Edit: Almost a year later. I've now had the lens for just about a year and I've taken thousands of pictures. Just about everything I initially said I would say again. Two things I'd add: First, barrel distortion is quite noticeable at short focal lengths. This can be objectionable where there are things near the edges of the scene that should be straight lines (roof lines, highway bridges, etc.) that appear curved. This is expected with any lens at "fish eye" wide angle, and so it is with this lens. I've found that this effect can be entirely removed in a decent photo editing program like Gimp or Photoshop. Look in the menus for the tool for lens distortion effects. Second, there is strange focusing behavior using this lens on my Canon XTi when using a circular polarizing filter. One should never attempt to use a simple polarizing filter on a digital SLR because they mess up the camera's auto focus. But circular polarizers are supposed to work, according to the literature. Still, the circular polarizer that I've been trying to use seems to cause the camera some focus indecision, especially with far focus. Don't count on being able to use a circular polarizing filter with this lens if you have a camera similar to mine. Of course, Nikon might behave differently. Edit: Almost two years later. This lens has become my primary lens. It's the lens that stays on my camera in the bag, with the other lenses in the pockets. It's just a fantastic general-shooting lens. I've come to really appreciate the optical image stabilization. It's giving me an extra stop or two of usable range in low light. I would never have considered using an f3.5-6.3 lens in low light before this. But, Tamron's stabilization works. If the subject isn't moving, hand-held slow-shutter-speed photography is possible where it never was before except with a wide aperture lens. Just two days ago I was out in the boonies of Arizona shooting telephoto pix of javelina in low-light conditions that would have been impossible with any other lens. After a considerable amount of use the lens has developed some tendency for 'lens creep' (see above). It's not a problem, but it does happen. Use the locking lug. I remain delighted with this lens. Edit: Almost 3 years later. Nothing really to add. This remains my primary lens. Aperture priority at f6.7 to minimize chromatic aberration for general shooting. Yup, "lens creep" has set in. Point the lens down at a steep angle and ploop, there go the front elements. A minor annoyance. Glad I bought it. Edit: Four years later. I recently upgraded my Canon XTi body to a T3i body. This lens remains my primary lens. The T3i has better signal-to-noise ratio (translate: higher ISO capability) from the sensor than the older body, which combined with this lens significantly improves low-light performance. I've found myself doing much more creative low-light photography than I ever would have imagined possible just five years ago. Going out at night to set up scenes in moonlight or candlelight has become fun! This lens remains a perfect match for the Canon line of advanced amateur camera bodies with APS sensors.