Tuesday, December 18, 2012

Auto aperture adjustment

The aperture is the iris inside the lens that determines how much light reaches the sensor in the camera. This has a massive impact on image quality, and not just whether it’s too dark, too bright, or just right. Depth-of-field, focus and image quality are all influenced by the size of the aperture, (which is reported in f-stops.)

And why am I rambling on about this today?

Well in machine vision we normally use lenses with a manual aperture. We dial it in to the optimum setting (typically around an f-stop of 2,) and lock it in to place. But sometimes it would be useful to be able to adjust it, preferably without clambering inside a machine to reach the camera (from where you can never see the monitor anyway.) And that’s why aperture control might be of interest.

What I didn’t know until today though us that there are two types of aperture control; DC iris and P iris. How did I learn about this? By reading “Auto iris control with Point Grey cameras” in the Point Grey Knowledge Base. This gives a good summary of the differences between the two; it’s worth a couple of minutes of your time.

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