Here's something of an albatross. It's a Nikon Nikkor 28mm f/3.5 PC (perspective control) lens. I bought it years ago for around 550USD back when I thought it would be just the ticket for taking photographs of buildings. Yet over the now many years it's been shot in anger very few times. It followed me to Europe and, even now, rests peacefully in the Toy Box as a rather expensive testament to my lack of impulse control.
What makes this lens "special" is it's vast field of view and unique barrel construction. It covers a much broader area than is normally required by a 35mm full frame lens. The lens barrel allows sliding movements of up to 11mm's. This is a shift lens.
Shift lenses are great for situations where you want to avoid "keystone" optical effects when photographing subjects such as tall buildings. If you level the camera where the plane of focus is parallel to the plane of the subject you can shift the lens to include more of a building (for example) and less of the foreground. Looking at this image the vertical lines remain parallel and I was able to eliminate a lot of the uninteresting foreground but shifting the lens up.
This lens is not a tilt/shift. In those kinds of lenses you can not only shift a lens (decenter it) you can also tilt the plane of focus. Because of the more complex barrel mechanism these tend to be rather expensive (and well out of my price range, particularly these days). Tilt/shift lenses provide imaging flexibilities similar to an old fashioned large format film camera. Changing the alignment of the focus plane to the subject allows a user to manage what portions of the scene are in focus and which are not.
The reason my lens sits largely unused and unloved is that modern image processing software usually have "keystone" correction functions. You can make vertical lines parallel very quickly and easily on a computer. This, in turn, removes the "need" for a specialized lens and has put downward pressure on prices of these old shift optics.
Other than when deliberately used because I feel guilty, I don't really know what to do with it, so this pretty Nikon Nikkor 28mm f/3.5 PC Albatross sits in the Toy Box. I wonder if someone would like to trade with me for another "interesting" lens?