While out shooting at the weekend, I found myself discussing (with myself!) the merits of Tilt/Shift lenses for the subject matter which I was working on, namely architecture.
A tilt/shift or perspective control lens is unique style of camera lens, which allows the user to independently move one part of the lens relative to the cameras sensor, and thus enable you to achieve straight verticals & horizontals to basically display an image as your eye would see it, eliminating the distortion that occurs with wide angle lenses.
This is particularly useful when shooting interiors and exteriors of property as you can ensure 'in-camera' that your verticals are indeed vertical, which is important in real-estate photography and architectural photography in particular. Sometimes you can be shooting subjects like this and for the effect or look you want this is not important and a slant or angle to the shot can be the desired effect. These lenses are also capable of creating fascinating effects with control over the depth-of-field of an image: sometimes they are used to create the 'toy' look to scenes where a photograph initially looks like a scale model instead of reality.
These perspective control effects can also be emulated using various software programs quite successfully, but only with care and attention.
Nikon makes a couple (or three) of these lenses in different fixed-focal lengths, 24mm, 45mm and 85mm and due to their specialist nature they are quite pricey, although there are a couple of third-party alternatives now which offer very good results for less outlay.
With any luck, I might be able to rent of these in the near future to give it a trial run for myself outdoors!