Q: I am reasonably new to digital photography and recently bought a second lens for my Nikon D90. However I am now paranoid that changing the lens will allow dust to get on the sensor and in the worst case damage it. I was wondering if you could suggest environments that are safer to change the lens or places to avoid? Also, what is the most effective way of checking if the sensor has dust on it and what should I look for?
A: You’re not paranoid if they really are out to get you! Dust is a real issue for users of DSLR cameras and you’re wise to be concerned about it. That said, most manufacturers – including Nikon – have good dust-control procedures these days so it’s not the problem it used to be.
Common dust-reduction strategies include vibrating the sensor so dust falls off onto a sticky strip; putting a charge across the filter to repel dust, designing the mirror chamber to generate airflow to dislodge dust, and software solutions which map the location of dust specks and clone nearby pixels to hide them.
Where should you change lenses? In my experience there is only one place where you should never, ever change a lens – the Pilbara in Western Australia. This is a landscape composed almost entirely of what appears to be red talcum powder – except for the bits that are made of asbestos! The people there aren’t sunburnt – they are stained red. When I got back from there a couple of years back, my Canon EOS 5D needed a professional clean-out and my Ricoh GR-D lens had jammed.
That’s an extreme case and mostly you can stay dust free by following a few simple rules:
1. Turn the camera off before switching lenses – the sensor can carry a charge that attracts dust.
2. Try to keep the lens mount pointing towards the ground when you change lenses. Dust falls down and if the front of the camera is pointing down you will get less dust falling into the camera.
3. Don’t wave a camera body around without a lens on it – the goal is to change lenses as quickly as possible. If you don't have a lens to attach to your camera straight away, use a body cap.
4. If you're in a particularly dusty environment, change lenses as seldom as possible – when you do change try to do it somewhere less dusty, like in the car or indoors – ideally in an air conditioned room.
Professionals can often afford to ignore rules like these, especially sports photographers. After all, they are working very quickly, they have someone to clean up their images and their gear gets serviced regularly.
How can you tell if you have dust stuck to your sensor filter? Here’s a simple trick. Take a picture of a blue sky, or any single-colour surface with minimal texture. A white or pale wall is fine. But do it with the lens stopped down to f16 or f22 – as low as it will go.
Examine the image on a computer screen. If there’s dust on your sensor filter it will show up in your image as a grey spot.
OK, so now you’ve found dust what do you do now. Panic? Curl up in the foetal position and sob? Trade your camera in on a new one?
It’s not that serious, really! In fact, in most cases you can probably just ignore it. If you have to go to a 100% view on your screen to see it, it’s going to disappear into the detail of most shots. I shoot in a studio against a blank wall or background paper and I don’t have
much trouble.
If your spots are bigger you have a few options to get rid of them. The first step is to check your manual for advice. Some manufacturers recommend using a blower or brush to remove the offending particles. As far as blowers go, the Giottos Rocket is great. You first need to lock the mirror up and your manual should have instructions as to how to do that.
Remember, if a speck appears in the top of an image, the dust particle is on the bottom of the sensor unit. If you don’t have any success with the blower, you might be able to try a light brush if your manual recommends it. A big soft makeup brush works best, though obviously it should be brand new. Brush twice, very gently, in each direction, hardly touching the glass. The dust will stick to the hairs so you hardly need to touch the filter. Finally, blow out any dislodged, floating dust with a hand blower.
Finally, if that doesn’t work there are kits to wet-clean a sensor if you’re brave enough to DIY. I’m not, so if it’s that bad it goes in for a service.
Story by Andrew Fildes. First published in Digital Photography + Design.
Find the dust: Dust tends to be more noticeable in areas of low detail, such as skies and painted surfaces. It’s also easier to see on screen than it is in print.