Canon has the largest range of tilt and shift lenses of any digital SLR system with the TS-E 17mm f/4L, TS-E 24mm f/3.5L II, the TS-E 45mm f/2.8 and the TS-E 90mm f/2.8. The original TS-E 24mm f/3.5L is also still in the market even if it's not made by Canon anymore. What makes TS-E lenses special is the range of movements of the lens assembly relative to the focal plane. Unsurprisingly the Canon lenses offer tilt and shift movements as their name would suggest.
First why the designation TS-E? Other Canon lenses for EOS cameras are EF or EF-S, but these special tilt shift lenses are not auto focus lenses so the EF or Electro Focus designation doesn't fit.
Since the movement of the tilt and the shift have different effects on the images we'll cover each of the two kinds of image results in isolation to make it clear, though the combination of the two is most powerful. For this article we'll look at shift, and use the video modes of the latest EOS digital SLRs to make the effect totally understandable. Tilt will be covered in a future article.
In this video above the TS-E 45mm f/2.8 is fitted to our camera and the lens shifted parallel to the sensor all the way to the top limit of it's movement. Then in the first part of the video it's shifted down to the centre stop where a small indentation let's you know you've reached the centre of the movement, and in effect at this point the lens becomes a normal 45mm lens. Second part continues the movement of the lens from the centre to the lower limit. Watch how the trees in the video keep upright and how the video shows that the relatively small range of movements can change what is in the picture by so much. Use a hotshoe mounted spirit level to make sure the camera is level during the shoot to keep the trees upright. Sure you could try and frame the scene by tilting the camera, back to get the tops of the trees in, but then the trees will start to look smaller to the top and bigger to the bottom. This shift is like moving the camera up or down, and not just by a few millimetres.
TS-E lenses offer the ability to rotate the tilt and shift planes relative to the camera. This makes the seemingly impossible pictures possible. For example if you need to take a picture of a person who is stood in front of a mirror then you can shift the lens sideways and take the picture, the photographer will be simply out of the frame and importantly not showing in the mirror! Widely thought to be only useful for architecture, interiors and technical imagery the TS-E lenses offer amazing possibilities for creative photographers.
For more reading then check some of these links to the Scheimpflug principle,and an article on the TS-E 45mm lens on CPN. If you want to see the TS-E 24mm f/3.5L II 'dance' then check out the bottom of this preview article at dpreview.