Being of the newer Pro Back design, this particular back uses a fibre optic lens on the back itself to project the image onto the polaroid film plane. This results in a much higher quality image compared some of the older NPC backs. And more importantly, this back is able to provide full frame polaroids in the format of the camera, unlike many other backs which only offer a cropped image which is often too small to be useful. It's a niche market and obviously the prices reflect that as well. The new back costs US$900 and I'm sure the limited manufacturing runs add to the high cost of the item.