I’m trying to determine the difference, end result-wise between, DC Iris and AES. My background is in photography so my first thought is that DC Iris is similar to aperture priority and AES is similar to shutter priority. Is this correct?

From what I’ve read, DC Iris is used when the camera is mounted in a location where the brightness level changes frequently. If this is correct, and DC Iris is similar to aperture priority, then the depth of field (what’s in focus) would change as the iris changes size. Is this correct?

If the iris is fixed, and the shutter speed changes, then there should be a greater likelihood of getting blurred moving objects in low light situations. Is this correct?

In photography it is possible to get the same photo using either aperture priority (DC Iris) or shutter priority (AES) from the standpoint of exposure, depth of field may be different or images may be blurred, but the image exposure would be the same.

So what’s the benefit of using DC Iris over AES, if both can product an equally well “exposed” image?

Thanks.

DC Iris (or auto-iris, since video iris is basically the same), actually opens and closes an iris in the lens using a motor and an electronic signal from the camera. AES only electronically varies how long the individual pixels are addressed. It works similar to a shutter, but its operation is purely electronic and is not capable of handling as wide a variation in lighting as an auto-iris lens. AES, however, responds much faster to lighting variations than auto-iris.

Your comparison with photography is pretty accurate and the reason we'd use shutter over iris is usually cost. A fixed lens costs less than a motorised one. There are advantages to motorised lenses but they cost more.

The big differences are the depth of field and smearing. In CCTV we want low light perfomance so if we use a fixed iris lens with shutter we will always set the iris wide open and as a consequence we end up with reduced depth of field. A motorised lens will give us more depth of field during the day. Smearing is less of a problem nowadays but CCD's can suffer under extreme bright light, light bleeds into the registers and you get vertical streaks. A motorised lens stops this.

The blurring you refer to isn't usually an issue with either shutter or motorised lens as both will have the same max shutter exposure.