The film is moved through the telecine machine mechanically. If the mechanics of the telecine machine are not precisely set up, the film can weave backwards and forwards as it passes through the machine, with the result that the final video image wobbles from side-to-side as well.
Telecines are not the only source of wobble in a
video image, however. Wobble can also be introduced by the original camera
shooting the film if its mechanism is not perfect.
Dune (Original Release) 0:05-0:10
Note the titles wobbling from side-to-side