What is the difference between Auto Iris and Direct Drive Lenses?

An Auto Iris lens is one that automatically adjusts its iris for changes in the scene lighting levels. The motor that opens and closes the iris is driven by an Amplifier that processes a small electronic signal changing with the light level.

A Direct Drive 'DD' lens does not have this Amplifier and can only operate with a camera fitted with one.

A camera specification will indicate the available output options.