Big and heavy, but beautiful.
You may obtain very crisp images from this lens, but you have to put it on a rock-solid tripod (or shoot whit a lot of light at high speeds), maybe interlocking something between the tripod mount and the lens itself to avoid vibrations (often a rollfilm plastic case filled with something is good enough).
It could be a useful travel companion, but for my tastes is too dark, so I use it mainly for landscape and macro work.
It is sharp wide open, and past two stops down don’t improve so much.
(Will not work on full frame, on DX equivalent to a 15-30mm)
A very good performer indeed, if you don’t care about it’s border sharpness (only so-so).
If you need it as a reportage lens buy it and you will not regret your money; if you want it to use as a landscape lens try to test it before you buy to see if it met your expectations.
For infrared use it is a “mixed bag” lens: really really sharp in the middle of the frame, but often with the borders not up to my standards and, only sometimes not everytime, a big hotspot in the middle.
Again: if you can try it before you buy it.
Rating: visible light