Motor for DC Auto Iris?

Usually a stepper motor is used for the auto iris because of the slower speeds obtained without need for gears, although a dc gear motor could be used. I have also encountered galvanometer operated auto iris on some older cameras. Recently, I experimented with a small (1/4" dia x 3/8" long) stepper motor from the auto focus of a 1/4" cctv camera. I set it up controlled by an Arduino micro controller using the MotorKnob example sketch. By varying a potentiometer, the position of the stepper's lead screw could be varied quite accurately.

Just go to ebay and search for "miniature stepper motor", and look for the ones with the lead screw, as those are likely to be designed for a camera application.

A stepper motor has 2 separate motor windings. The windings are energized in a sequence, and current is alternately reversed through the windings in this process. A magnetized rotor follows the sequence, causing the rotation. A micro controller can generate the sequence, and a motor driver integrated circuit like the SN754410 provides the current to drive the stepper coils.

Interestingly, the same type of motor driver can be used to provide bi-directional drive current for a dc gear motor. That gear motor would likely still require the analog amplifiers or micro controller to operate the iris based on a light sensor.