Principal design of film scanner

What are the principal design elements of a film scanner?

I do believe I have a decent understanding on how a flatbed is constructed, but I realize I have not the faintest idea on how a dedicated film scanner is constructed. Are they single element scanners, linear array scanners, or based on 2D sensor such as in a DSLR? What kind of optics are involved? Mechanics? Focusing systems? Lighting?

Is there a good source in the internet that I was not able to find when doing a quick google?

Have anyone heard of a decent DIY-project, except from the standard one of using a DSLR and some kind of back-lighting.

Help me satisfy my curiosity.

/Henrik

I've built a number of special purpose film scanners (mostly for some type of restoration project) It is very similar to the old days of slide copying. You are basically re-photographing a photograph that has a transparency component. So you need to think about all the elements in the image chain:

- the back light source (color temperature, field evenness, intensity)
- film carrier, needs to be in some type of rig that is holding the film flat and parallel to the camera's sensor
- optics of the imager
- the imager/sensor itself. (area array sensors make life easier, but are more costly)
- the image processing routines of the scanning software

The scanner is essentially an analog device and each element in the chain is important.

Here is an interesting open source project:
Kinograph v0.1 - DIY Film Scanner/Telecine - Machine Assembly