I believe the [Horizon camera][1] is an example of a [slit-scanning camera][2]. During the exposure, the lens assembly rotates from one end of the panoramic field to the other. A narrow slit is used to ensure that only a thin line of film is being exposed at any instant. The result is that the whole image is exposed using the center of the lens, which can form a high-quality image, and you don't get [distortion][3], which is typical on very wide-angle lenses.

One example of a digital scanning panoramic camera is the [Panoscan][4], which takes medium-format lenses, and scans mechanically to create an image using a trilinear CCD (one column of pixels in each of red, green, and blue) to form an image.


  [1]: http://www.kremlinoptics.com/catalog/item/horizon_s3_u_500_panoramic_camera.html
  [2]: http://en.wikipedia.org/wiki/Panoramic_photography#Full_rotation
  [3]: http://photo.stackexchange.com/questions/11054/what-are-barrel-and-pincushion-distortion-and-how-are-they-corrected
  [4]: http://www.panoscan.com/MK3/index.html