http://www.nikonchat.com/nikkor-12-24-lens-2/

Nikkor 12-24 second hand? or Tokina 11-16?
Hi all, I've been waiting a wide angle lens for quite some time and has the following opportunities to buy them: Whether a new Tokina 11-16, I've heard is excellent, if not better than the Nikkor. However, I'm afraid I might get a defective part (the has happened to a number of people and customer service where I live is not so great). In addition, cameras will work with the future of how a Nikkor 20 years old works almost perfectly with today's cameras? Or second hand Nikkor 12-24 f / 4. I just got the lens to try today and so far have been pretty images good. I can get for about $ 550. Unfortunately, the exterior glass elements are not so clean, the front and back with dust and minor scratches, along with what appears to be drops of water, and the claws are used. The person who offers me is a photographer must have used the lens a lot. My budget is somewhat less $ 650. Thanks.
difficult choice. The Nikon is an interesting target. However, what you describe that looks like water droplets can be fungi. If it appears be in one of the internal elements that would be very, very careful of that lens. Fungus can be stopped, but requires a full stop dismantling to be expensive. Was provided used in a wet environment? The tokina … I've worn once and was very, very impressed with it.It will give more brake light that can be useful. With regard to future-proof. I have bought and sold a lot of Nikon mount lenses in recent years of various brands. The lens only time we found was a 1980 19-35 f3.5, which happened to have the tokina ID card in it (but the same lens is sold under different names quite a few). With that lens my body was convinced that would be open to F1.1. Surprising at first, but quickly learned to deal with it. Now with Canon know where some very good third party lenses had to be updated to follow working. Malignant samples can happen to any brand, including Nikon. The best solution would be to buy the ens in a store that allows you to test it in the store or to change after a few days. So .. . Think if you want extra stop, think about what I said about fungi as possible.