What is the difference between no iris and auto iris ?
The iris controls how much light is let into the camera lens. In the old days, cameras came with no iris control. If you needed to control the light levels you would have to purchase a special lens. Nowadays, most cameras come with automatic shutters which perform the same function as the iris – controlling how much light is let into the camera. Unless you have an application with extreme light levels (like at a beach) you probably won’t need a special lens with iris control.
