Monday, June 5th 2006

Aperture and Sensor Dust

One of the main problems with digital SLRs is their tendency to collect dust on the sensor. Every time you change lenses you risk getting more dust on the sensor.

I noticed dust on my sensor the other day when taking pictures of lightning, since I was using a very small aperture – f/22. (The dust only shows up in pictures taken with a small aperture.)

I thought I’d investigate how small apertures you can use without the dust becoming visible.

I simply shot a series of photos of my white wardrobe door, out of focus, at different aperture sizes.

I decided to make a little animation, running from f/4.5 to f/36:

Series of shots taken to illustrate how visible sensor dust is at different apertures.

It seems as if you won’t see the dust at all if you stick to f/8 or lower, and in most scenes you would probably not be able to find the dust at f/11 either. At f/16 you might see the dust in large single-coloured areas. Apertures f/22 and up should be used with care, since you risk getting very sharp black dots in the picture.

The good thing is that you seldom need more than f/8 or f/11 to get the depth of field you want, at least on crop SLRs such as the 30D and 350D. In other words, you shouldn’t miss those very small apertures much.

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