Ian Evenden

The sensor of a DSLR camera is tucked behind the reflex mirror – as such, the camera has to be switched on while you clean it

Dust build-up on a camera sensor can lead to dark blobs on your DSLR images, which in the case of astronomical photos can obscure detail and darken the brightest parts of a planet or nebula – a particularly galling scenario when you’ve gone to so much trouble to capture that light in the first place. While these artefacts can often be removed in image-editing software with cloning or healing tools, it’s best to treat the problem at its source. That means taking the plunge and cleaning the camera’s sensor.

The sensor of a DSLR camera hides behind a reflex mirror, which deflects the light coming from the lens up into the prism that forms the viewfinder. It flips out of the way when an exposure is made or the camera is used in live view mode, and thus provides a certain degree of dust-proofing, but the tiny

motes can and will still get in. The air displacement caused by zoom lenses moving their elements around, for example, can suck dust in.

Dust-reducing systems are built-in to many modern DSLRs (look for the ‘sensor cleaning’ message on the screen as you turn the camera on and off) and these do a decent job of shaking light dust particles from the sensor by vibrating it at ultrasonic speeds.

Before and after

Before you clean your sensor, take a test shot. Pop on a lens, stop it down to f/22, and take a photo of the sky during the day (taking care not to aim at the Sun of course) or a plain white wall, then increase the contrast in an editing app. The resulting image won’t be the finest you’ve ever taken – in fact it will probably be a noisy mess – but it will highlight the condition of your