I got a used Tamron 200-500 f/5-6.3 on eBay, and today was the first sunny day we've had since it arrived over two weeks ago. I went out to a local state park to play with it, intending to do a full battery of shots, and I ended up shooting at only the longest reach, although I did pick several subjects and distances.
This thread is more about the lens rather than the images, and trying to decide whether to keep it or put it back on eBay and get some money back.
It doesn't auto-focus on my D5000 (no focus motor in the body) which I knew going in, but focusing turns out to be more difficult than I expected. With "modern" viewscreens lacking the split-image we used to count on, the only indication is how it looks in the viewfinder, and if you happen to be able to look down, maybe you'll catch the "in-focus" dot lighting up at the bottom of the viewfinder. But breathing on the focus ring moves it far enough to ruin the focus.
First frame is a blue heron in flight, from about 200 feet away. The crop (on this and the next two images) is pixel-for-pixel without resizing (if you look at the full-size image) and I really don't know if the lack of sharpness is the lens, the distance, or not quite focused. I'm thinking 300 feet is just a bit of a reach.
Even more extreme, this egret was 300 or 400 feet distant. I'll come back to this image later.
Egret gathering nesting material, followed by a shot of the trees on their island, showing the nesting density.
Another blue heron, from about 50 feet:
Same guy from about 10 feet:
Mockingbird on the ground. (Florida's state bird, it's really pretty hard NOT to find one somewhere!)
Another individual, apparently following the first one around. Stalking, sort of.
Courtship display?
I bought the lens for what I did with it today, and perhaps as a sports lens. I can't focus fast enough with it to use it for sports, though, if today is any indication. I gave less than 600 bucks for it, so I can't fault the price. Besides the focus difficulty, I find the bokeh rather annoying. Items out of the depth of field don't simply blur, the lens seems to "copy" them vertically. In the last image look at the twig coming forward from the right wing. This is where I come back to the second image, that I said I'd come back to. Look at how this effect paints the background.
So I may not keep this lens. I've always wanted a really long lens to play with, but unless I get a body with a focus motor, this one may just be too difficult to use. OTOH, the images I got of near subjects (10 to 50 feet) are quite satisfactory, to me anyway. So maybe I'll put it back on eBay in a few weeks after playing with it some more, maybe I'll keep it.