So why do sensors collect dust, and how do you detect it, and what do you do about it?

A sensor is just an electronic negative. But it collects dust for two reasons: one, it never changes (unlike a real negative, which changes for ever shot); and two, it is electrical and can therefore get electrostatically charged, meaning it attracts fine dust particles.

This dust can show up in images where you use a small aperture (like f/16) and have an even surface (like the sky). It looks like this:

So how do you know if you have dust on your sensor?

You do. Everyone does. Do not worry about it unduly – unless it shows up in images! But if you really want to know, here’s how:

1. Set your camera to aperture mode (A/Av).
2. Select a low ISO.
3. Select an aperture of f/16 or f/22 or even f/32.
4. Set the lens to wide
5. Focus manually to the closest distance
6. Point at, and fill the entire frame with, a clear surface like a white wall
7. Shoot – and move your camera about while shooting.

You will now, when you zoom right in, see the dust.

If is it annoying, then go about removing it in the following ways:

1. Use the camera’s anti-dust feature repeatedly.
2. If that does not work, ensure you have a 100% full battery and use a blower (set the camera to manual cleaning, or bulb mode, open up, and carefully use a rubber bulb blower.
3. If that fails, the safest way is to have it done by your camera maker.
4. Alternately, use the Visible Dust rotating brush first.
5. And finally, when even that fails, use wet pads.

The wet pad process is annoying and scary. You will clean some dust but deposit new dust. (Test after each attempt). You will see smears. You have to carefully repeat this process a number of times until you are finally dust free.

Finally: prevention etc: always minimise lens changes and when you do change lenses, carry the changes out with the camera pointed down. Store your camera with a lens attached, always.