this is designed with the Nikon DX sensors in mind so is designed around the 1.5 (average) crop.
it is a true 180* veiw making it great for landscapes and depending on how you tilt it you can create some great effects.
i have also used this in portraiture (more specifically events and weddings) and its pretty sharpe and creates a really nice unique effect.
needless to say its a fish eye so you suffer from Distortion depedning on what you use it for (e.g. close subjects) but the effect adds flair to some otherwise BORING images with say an 18mm.
ive used this lens all over europe and never once have i experienced flare in an image, even when i deliberatly tried! a very rare thing to experience in such a wide angle lens.
There is a manual focus ring on it should you want to focus that way but you have to switch the camera so Manual focus, you cant just overide like the SWM lenses.
its a very sharpe lens through out the F stop range. well as of yet i havent found an F stop that creates a softer look but theres still time.
ITS WATER TIGHT!!! as long as its on the camera,,, i got caught out in a terrible rain storm, when i got back to the hotel (soaked through, camera in a bag that was as good as a reservoir!) checking the camera body and lens not a drop had got through the seals. AMAZING"!
BAD POINTS:
its the old Screw driver type focusing so its not compatible with the Nikon D40x but is with the rest of the models
being a DX lens its not really compatible with the FX sensors (full frame) like the D3, New D700 as there would be some Vignetting around the edges.
the built in lens hood is probably useless, i have no doubt if i dropped this on concrete it wouldent stand a chance.
the only way of mounting filters on this if through the back of the lens, and i havent yet found a filter small enough or something i can trim to fit.
its externally focusing so the front eliment zooms in and out but its so minor you dont really notice.
be carefull not to get your feat in the frame! ime seriousa slight slip while ime takking a shot and many times ive got my toes in the photo.
SUMMERY:
despite the minor bad points i find the a great versitile lens to have in my bag, its limitations are only level to the photographers imagination.
personally for me its a lens i dont regret buying, it doesent just sit in my bag just in case i need it it gets used and to good effect.
all the problems i were worryed about like flare and seeking for focus, soft points in the apature just dont happen so that alone justifys the price tag.
ALSO its an F2 lens it works amazingly well in low light! ive captures sunsets at 125th second before now.
fantastic lens, optics very sharp, but it is a lens you will not use all of the time, you have to really think about how or what you are going to use it for