Anti Dust Feature of Digital Slr Cameras

by : Or Hillel

Digital cameras use a sensor known as CCD in order to convert light energy to pixels. Dust that accumulates on the CCD can result in black pixels or imperfections in the photo as it blocks light energy from hitting parts of the CCD. We will go over a few solutions for eliminating dust on the CCD.

The CCD sensor is located behind the reflex mirror in a digital SLR camera. When taking a photo the mirror moves and lets the light coming through the lenses hit the CCD which then converts the light to a series of pixels comprising the digital photo. Most of the time the camera is closed and dust can not penetrate it. Some cameras might not be completely sealed against dust resulting in dust penetrating he camera's body even with the lenses installed. However in most cases the majority of dust exposure is when lenses are replaced. During that time the camera is open and exposed to air and dust.

In order to minimize dust on the CCD make sure that you minimize the time in which the camera is open and exposed to air. For example when changing lenses make sure that you are in a relatively clean environment and that you have the second lenses handy. Try to avoid changing lenses when in windy or dusty environment. Never take the lenses off a camera and leave the body open and exposed - either install other lenses or put a seal on the body to prevent dust penetration.

Even with careful care dust will eventually find its way into the camera and on the CCD. There are a few ways to get rid of that dust. Depending on your camera some of them will not be available to you.

Active dust removal: Most new SLR cameras include some sort of active dust removal mechanism. The most common one is anti dust vibration. This solution removes dust from the sensor by vibrating it in high frequency for a short period of time. Vibrating the CCD will result in dust falling off the CCD or "dancing its way" from the CCD. Different cameras turn the anti dust vibration at different times. Some cameras turn it on every time the camera is switched on, some every time it is switched off and some both when the camera is switched on and when it is switched off. Other cameras turn the vibration on periodically or let the user turn it manually.

Cameras that include an image stabilizer based on sensor movement usually also include anti dust vibration since they already include the mechanical part: a motor that can move the sensor and thus the anti dust vibration is a simply software addition.

Passive dust prevention: Passive solution that tries to eliminate some of the causes for dust accumulating on the CCD. The main reason that draws dust to the CCD is static charge. Some manufacturers add an anti-static coating on the outer layer of the CCD (usually this is the low pass filter layer). By doing that the CCD is less likely to attract dust due to its static charge.

Manual dust removal: Manual removal is simply a way for you to manually clean the CCD. When put in manual dust removal mode the camera moves the mirror and keeps it in a position where the CCD is exposed and is reachable. At that time you can try to blow off dust from the CCD for example by using an air blower. You could also use special cloth in order to clean the CCD but be very careful when doing that and make sure you read the manufacturers instructions for how to clean the CCD without damaging it. If you're not sure how to clean the CCD it is better not to attempt cleaning as it can be easily damaged.

All dust removal methods have their limitations. Adhesive dust or other material is either very hard to clean or impossible to clean. Eliminating dust completely from the CCD is impossible but by applying care and the mentioned features most of the dust that results in photo imperfections can be avoided. For the casual photographer the built-in active or passive anti dust features should be enough and manual cleaning will not be needed.