A basic rule of thumb is that MI lenses should only be used in internal applications. This is because you rely on the camera's electronic circuitry to compensate for light fluctuations in the scene, which cannot compensate to the same extent as an Auto Iris lens.

Manual iris lenses allow you to regulate your iris by spinning a ring on the lens manually. Though the iris can be controlled from fully open to fully closed, most manufacturers recommend setting manual iris lenses to totally or 90%+ open to preserve low light.

Read More: How do you choose the correct camera for your application?