Tamron Adaptall 70-210mm f/3.8-4

General
There are plenty of Adaptall lenses going around, and this used to be a very smartly conceived thing back in the old days. Basically, there was only one lens, and with different adapters you could use it on different cameras. Nowadays, we have autofocus systems and complex (sort of) electronics, which require a special mount for each brand (Nikon, Canon, and so on). But for some people this is still an interesting option, as it is very, very cheap lens. I got a copy for 20$ including a genuine Adaptall mount for Nikon

Pros/Cons
+ very cheap
+ more than decent image quality
+ fast at the long end (f/4 instead of the usual f/5.6)

- manual focus + tele = not the best combination
- the Adaptall system is completely obsolete; it has no meaning today
- heavy; heavier than any consumer modern zoom

At 200mm and fully open (f/4) it certainly is very strong, better than the consumer Nikkor tele zooms at the same settings

Intended Users
Great for:

• experimenting with some old film camera
• if you have less than 20$ to spend and you want a good quality tele, this is better than any other.
• using an Adaptall-to-m4/3 adapter, this would make a great lens for video use on a mirrorless

Not for:

• anything moving (manual focus, remember?)
• people disliking heavy lenses. This one is a heavy chunk of glass and metal
• if you can afford the cheap Nikkor tele zooms, they're better in every way except performance and aperture at 200mm

Final Verdict
Great value; 20$ for such a good lens is literally nothing. Having said that, its usefulness is questionable today. Manual focus lenses are tricky, and teles even more so. For some subjects it could be just fine (say, static landscapes). The fact that it's faster than other lenses at 200mm can be important for some applications. One possibly interesting use for this lens would be as a tele for video work on a micro 4/3 camera. Its manual focus ring is superb, offering precision adjustment. For 20$, it's worth at least a try!