Despite my recent unfavourable comments to an earlier review I finally decided to purchase this lens, mostly because for an 800mm lens it is cheap, and unless I win the lottery I am never going to pay £7-8k for a Nikon telephoto lens.
When I attached the supplied T mount adaptor to the lens I found it to be loose allowing the whole lens to rotate, I found three fixing screws around the circumference which could be tightened down to stop this, fix the lens to your camera first so the lens is the right way up when you tighten these, the screws are not very obvious and appear to be hexagonal headed, I could not find an hex key to fit but eventually found a jewellers screwdriver that did the job, the screws were very tight, making me wonder if I was doing the right thing at first.
There were no instructions to tell me to do this and no tool supplied to give me a clue as to what needed doing.
The first thing I found when I tried it with my Nikon D80 was that the camera did not know the aperture of the lens, I had assumed that although the lens is fixed at F8, there would have been some feedback to the camera to allow the metering to work, but the only way I could get it to work was by setting the camera to manual and guessing the shutter speed.
The focusing is manual only, it is very coarse and difficult to get right, which could be a dissadvantage if you are trying to photograph a bird before it flies away.
I did not however consider it to be too heavy, it is lighter than my 50-500 Sigma plus 2 x converter which is the only other way I could get this sort of magnification, I had hoped that its more compact size might let me get away with a tripod, but no, you definately need a tripod.
Presumably because it probably has less glass to hold back the light than the 50-500 and 2 x converter the images appear brighter, and two images out of the twenty I have taken with it so far were not bad!
It is a lens that needs patience, practice and to be a good judge of exposure, something which I suspect most of us have lost a little of, mostly due to modern cameras doing everything for you.
Build quality seems surprisingly good, it is solid and metallic.
If you need a lens with that sort of magnification for professional reasons, then sorry you are going to have to spend a few thousand pounds, if you are a keen amateur like me who can afford to risk a couple of hundred on this, then go for it, you probably will not be dissapointed.
I would recommend that you save a bit more and buy a zoom lens with a range up to 500mm before you look at buying this, you will find it far more useful.