I've had mine since January and it hardly ever comes off my Nikon D70 nowadays! I used to use a cheap Nikkor 70-300 G lens, but found the range to be too limiting. It was a toss-up between the Tamron and the Sigma 50-500. Went for the Tamron because it was a newer model and the optics would therefore probably be better.
The lens is great, although it is nearly half a metre long with the hood on and set at 500mm. Not too heavy though. I tend to use it with a monopod.
It gives best results at f6.3, which is good as this is what it is usually set at, given that i usually want a shutter speed of at least 1/500th. Even on cloudy days i can manage this (although i sometimes have to use 400 ISO).
Personally, i'd recommend the lens (in fact i may treat myself to the companion lens - the 28-300mm - in the near future).
It seems to autofocus quite well, although i haven't really got anything to compare it with. Occasionally it is a little slow - but then most long lenses struggle in dull light. Not a big problem though, as i just focus manually which is easy with the position of the focussing ring).
It comes with a good, light (magnesium) tripod mount, which i leave fixed to the monopod. Removing this is very easy and quick.
Quality of the images? Well - far better than those from my old Nikkor lens! Take a look at the pictures in
My gallery - most of these were taken with the Tamron lens.
Feel free to ask me any furthur questions.