Guys, just have a look at the Arecont-FAQ:
When should the user choose auto-iris option?
Many AV cameras support auto-iris option. These cameras are: AV1300-AI, AV2100-AI, AV3100-AI and AV5100-AI. Auto-iris option allows keeping the lens optimally closed when there is sufficient scene illumination, providing good depth of focus. When the illumination diminishes the camera opens the lens, allowing more light to reach the sensor, thus extending the sensitivity range of the camera. Auto-iris option should only be used for outdoor applications, where there is a large variation in illumination conditions. In many applications the auto-iris is unnecessary. It is important to keep in mind that the best image quality will be achieved with megapixel lenses. The auto-iris lenses available on the market today are not megapixel and will yield the images that are less crisp than those that can be obtained with manual megapixel lens.
There are also B&W Camera The AV3135 and the AV3130 have an B&W/colour (day and night) option.
Caution! Not all of the "experts" know everything!