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Tokina one of the independent lens manufacturers, albeit less well known than Tamron and Sigma. They do not have a very extensive range, but their lenses have a reputation for being well built.
I've owned their 80-400mm lens for two years now. I wanted as much reach as possible for as little money as possible and the Tokina fitted the bill best.
This lens is extremely well built. It's manufactured from metal, rather than plastic like most other lenses at the cheap end of the market, so is quite heavy. This weight does give the lens a solid feel, however. It does not feel as if it would fall apart if dropped. A tripod collar is built in.
I took this lens (fitted to my Canon 350D) on a boating holiday on the Norfolk Broads last year. The lens spent the whole week on a shelf under the windscreen, without any problems at all. Having the camera to hand meant that I could quickly take pictures and I managed to get some really good photos from that holiday, because of this. I'm sure a more expensive lens would have stayed in my cabin and I've have missed most of the shots I wanted.
The lens is very short in length for its focal length (It's marketed as the shortest 400mm lens in the world). This small size does mean that it fits well onto the smaller digital SLR cameras such as the Canon XXXD range.
The autofocus mechanism is not as fast or as accurate as other, more expensive lenses. The lens can seem to take an age going from one end of the focus range to the other. When it does get to the correct focus point, it has a tendency to 'hunt' especially in low light conditions (this is possibly not helped by the f/5.6 maximum aperture at 400mm). This is not, therefore an 'action' lens.
This lens does not have an internal autofocus mechanism and the end of the lens rotates when focusing. This makes it difficult to use a polariser.
One disconcerting aspect of the autofocus is that there's metal on metal contact when it hits the end of the focus range. The rotating part of the lens seems to crash to a stop. This sounds quite loud and violent, but mine has not broken anything, yet.
Optically, this is a bit of a mixed bag. Contrast is acceptable. Sharpness, whilst not excellent is pretty good for a 'budget' lens. Stopping the lens down a bit (f/8 or f/9) does improve the sharpness quite a bit. Stopping down also improves the quite noticeable chromatic aberration that this lens is prone to. I find anything under f/8 unusable if there are any high contrast areas in the frame (e.g. sky viewed through branches, or black and white objects).
Overall, this lens is excellent value for money. The image quality is pretty good (as long as you avoid shooting wide open), and its relatively small size makes this a very useful travel lens. The build quality is brilliant and it will take a bit of punishment. It's not the final word in sharpness, but then it's not the most expensive lens on the market either.