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Digital SLR Cleaning for Beginners

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The basic internal parts of a Digital Single Lens Reflex Camera

Compared to a compact snapshot camera, the modern DSLR is a complex piece of electromechanical engineering. The imaging sensor is hidden deep inside the camera and it is not immediately accessible for cleaning.

Before any attempt is made at cleaning the user should ensure they are familiar with the components inside the lens mount of their DSLR.

DSLR Lens Mount & Mirror Box

When you remove the lens from your DSLR and look inside the lens mount, you will see the mirror. This component is designed to reflect the image upwards onto the focussing screen. However, unlike a normal mirror, it is semi-silvered. I.e. it also lets a portion of light through the mirror. This light is reflected by a small secondary mirror onto the metering sensors at the bottom of the mirror box. The semi-silvered main mirror is extremely delicate and easily scratched.

DSLR Lens Mount & Shutter

The main mirror swivels up to reveal the shutter behind. When an image is taken ( i.e. the shutter button is pressed) the mirror flips up ( blocking the focussing screen), the shutter opens and light from the lens hits the sensor behind to expose the image. In the image above, you can see the shutter is made up of a number of thin blades. The shutter blades are extremely fragile and should not be touched.

So, during an exposure, with the shutter open, the sensor is revealed.

DSLR Lens Mount & Sensor

Typical exposure times are measured in fractions of a second, so most camera manufactures provide a special mode on the camera that will lift the mirror and open the shutter to reveal the sensor so that it can be checked or cleaned. This mode is sometimes know as ‘Mirror Lock-Up’ or ‘Sensor Cleaning Mode’ and is usually accessed via the menu system on the rear LCD.

For example, on a Canon Camera

First make sure that the mode dial is not set to fully automatic ( Green Square)

Press menu and Rotate the Quick Control Dial

And select ‘Sensor Cleaning’ then press the ‘Set button’

Select OK and press set again to raise the mirror and open the shutter to access the sensor. When you have finished, turn the camera off, to close the shutter and reset the mirror.

And on Nikon cameras

Press Menu and use the multi-selector to choose Mirror Lock-up from the Set Up Menu

Press Enter

Select OK

Press the shutter button to raise the mirror and open the shutter to access the sensor.

When you have finished, turn the camera off, to close the shutter and reset the mirror.

Some older Nikons require that the camera is connected to a mains adaptor before allowing mirror lock up. It may be possible to update the cameras internal software (firmware) to allow mirror lock-up without requiring an external power supply.

Please consult your camera user manual carefully, to learn how use mirror lock properly. Always used a freshly charged battery when using mirror lock up. This will ensure that the camera has enough power to keep the shutter open while you clean or inspect the sensor.


If the shutter should close while you are cleaning the sensor, the camera will be damaged. Ensure you are competent at using mirror lock-up mode before attempting to clean your sensor.

Modern DSLR’s will disable the Mirror Lock-up function, if the power remaining in the battery is insufficient. But it makes more sense to ensure you have a freshly charged battery in any case.

The last component to be aware of inside the DSLR is the focussing screen. To see the focussing screen, remove the lens, tilt the camera back to and look at the plastic screen positioned above the mirror. During use, the lens focuses the image, which is reflected by the mirror onto the focussing screen. Thus the image you see in the camera viewfinder is being projected onto this screen by the lens and mirror. If you can see any dirty specks in your viewfinder, the contamination is usually on the focussing screen. We deal with cleaning this screen later in the article.

DSLR Focussing Screen

When the shutter is pressed to expose an image, the mirror flips up and the shutter opens to allow light from the lens to fall onto the sensor instead of the focussing screen. As the mirror flips up, it blocks the focussing screen which is why the image in the viewfinder ‘blacks out’ momentarily when you press the shutter.

Having read this section, you should now be familiar with the working parts of your camera, i.e the mirror, the shutter, the sensor and focussing screen. You should be aware of how delicate the shutter blades are and how open the shutter and raise the mirror to access the sensor. In the next section we consider the best strategy to clean the sensor when it has become contaminated.

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