here's the story:
yesterday I got a Contax RTS from a flee market with pro winder and Carl Zeiss Dataphot back. Now here's my question, whats a Zeiss Dataphot? Here's a pic of that thingy.
It did what every other data photo back does. It replaces the normal back to use light to print information onto the film.
This one is an early one and I think it just printed numbers so you could identify a roll.
Later ones became slimmer and printed the date too. http://www.mir.com.my/rb/photography/hardwares/classics/contax/shared/accessory/databack.htm
Basically a professional tool. If you were shooting a lot of film a day you could log it all and when the films came back you had an identification marker on the first frame.
Also helped to stop labs losing stuff.
Digital does it bigtime these days with exif data.
