Digital SLR Cleaning for Beginners
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Recognising when the sensor is contaminated.
For most photographers, sensor contamination usually manifests itself as unsightly dark ‘blobs’ that appear on the images. These are usually most noticeable in the sky area of outdoor shots. It’s also easier to see the contamination when viewing the images on a computer monitor rather than using the LCD screen on the rear of the camera. A key point to remember is that sensor contamination cannot be seen through the viewfinder. It can only be seen by viewing taken images, or by using a magnifying lens to physically examine the sensor. Dust specks visible through the viewfinder are usually caused by dirt on the focussing screen and we deal with this issue later in the article.
Dirt visible in the viewfinder is not sensor contamination.
The easiest way to test for sensor contamination is to take a nicely exposed image of a blue sky at a small aperture – say around F22.
Sky Shot – Full Frame
This shot shows some contamination near the bottom of the image.
Sky Shot Crop at 100%
Viewed at 100% the spots are easier to see….. If the imaging application you use supports an auto correct function (auto-levels in Photoshop®) its worth applying the correction as that can show up the fainter marks more clearly.
Sky Shot – Full Frame – Auto Levels
Clearly this sensor has many more contamination spots than were first visible.
Although this sensor looks quite bad, it is worth pointing out that images are rarely taken at F22 and at larger apertures, ( F8 or wider) many spots simply do not show. So, it not necessary to clean the sensor every time a dust speck arrives.
If a blue sky is not available for a test shot, try to shoot a uniform piece of grey cloud. You can also test using a clean sheet of white paper.
Hopefully, it is now clear how and why the sensor in a DSLR becomes contaminated and how you can check whether your sensor is contaminated or not. However, before you attempt to clean the camera, you should ensure that you are completely familiar with the internal parts of the camera and how they work, to ensure that you perform a successful clean.