The water drops produced some rays on the picture due to the long shutter speed. Results may also vary from person to person. Well, the general optical performance of the lens is disappointing - at least up to slide standards. At 300mm I would rate the performance as poor with a rather dull contrast performance and mediocre sharpness. Vignetting is no big problem.
Distortions are visible at the extreme end though within normal margins.
It has the usual metal mount with body made of quite high quality plastic. I found the surface of the lens to be very slippery - not very convenient when changing lenses. The lens also has a rotating front element. As usual the lens size extends when zooming towards the long end. The lens just features the std.