Sensor Dust

Dealing with the Dust

Do I need to say anything more. Anyone with a DSLR knows the frustration of dealing with the blotches on their images created by tiny of pieces of dust, pollen and hair which inevitably settle on the sensor and require long periods of painstaking editing to remove from the final images.

Dust Detected

Lightroom Ready for Spot Detection

Newport Sunrise : Cleaned

First I should point out that dust usually does not actually contaminate the sensor, instead it lands on the overlying glass anti-aliasing filter.  Although not as expensive as the sensor this piece of glass is liable to scratching and is not cheap to replace. We live in a dusty world and there is no way to fully avoid the problem of sensor contamination. Given that there is no completely satisfactory  cure for the problem, I have only a few incomplete thoughts on the subject of dealing with the dust.






Dust Avoidance.
Since prevention is always the best approach how can sensor dust be reduced or avoided. I can suggest only one absolutely reliable preventive measure, use a fixed lens camera or never change your lens. 

Canon SX50 HS

Dust almost always enters the camera at the time of lens changes and if the lens is never removed the sensor should remain pristine. In especially dusty environments, I will occasionally restrict myself to my fixed lens cameras. Actually dust can come from the shutter enclosed within fixed lens cameras, but modern cameras are designed to avoid this problem and the images from my Canon G11 or my SX50 have never shown dust spots. If I must use my DSLR in these situations I try to restrict my camera to one all-purpose lens and only consider changing the lens if I can find a protected area.

DON'T Changes Lens'

If lens changing is unavoidable I try, although not always successfully, to follow a careful lens switching technique. I start by getting my replacement lens ready for the switch. To reduce the time of exposure, I keep it close at hand. Since much of the dust comes from the internal element of the lens, I use my pocket rocket to blow away any contamination and I try to keep the internal lens cap clean. To keep gravity working for me, I try to keep both the open camera body and the lens pointing down. It is also important to be sure that the camera is turned off during lens changes. Power flowing to the sensor creates an electrical charge that can attract the dust particles.

 


Reducing the Dust Effect
 

Dusty Sky

You have been fanatic about following good "lens hygiene" and yet dust inevitably can match your efforts with an equal or greater fanatic attraction for the cozy environs of your sensor. Before we talk about approaches to dust removal there are a couple of steps that can help reduce the impact of the contamination.

 



The visibility of sensor dust on an image is closely related to the

Jaffrey Center Sky : Aperture Effect

camera aperture and since the dust actually lies on the filter overlying the sensor, the apparent sharpness of the dust particles is also related to the distance between the sensor and the anti-aliasing filter. The particles are much more obvious at small apertures. You can demonstrate this relationship by comparing images of a clear sky take at high and low f stops. In my example the dust is seen sharply at f22, but is only a vague smudge at f4. Obviously there are many factors that contribute to the decision to use a specific aperture, but if all else is equal a wide aperture can reduce the need for intense editing when you get home.


What You Can't See

Cut Out the Sky

Sensor dust is primarily a problem in bright homogeneous areas containing little detail. In other words it is mostly an issue in the sky. Reducing the impact of dust is just another reason why you may decide to minimize the amount of uninteresting sky in your images. I still scan all of my images for dust, including areas of high detail, but dust hidden among the forest greenery is much less likely to require cloning than the flecks seen overlying the clear sky.

 
Getting Rid of the Dust
There is a long list of techniques to physically remove sensor dust and as might be expected the most effective approaches are also those most likely to cause sensor damage, but let's start with the noninvasive techniques.


In-Camera Dust Removal
 Many cameras have built-in sensor cleaning functions. Automatic dust removal generally works by generating an ultrasonic vibration in the overlying anti-aliasing filter to dislodge the dust and allow it to fall to a dust collection area below the sensor. This works well for loose particles but sticky contamination such as pollen may not be removed.

 


Blowers
My next step is to use a blower. I use my Giotto Rocket blower to clean the lens elements as well as the sensor. My Canon 5d has a lens cleaning function which locks the mirror up to expose the sensor. I insert the blower right over the sensor and apply several vigorous squirts of air. I generally do this with the camera aimed down in hopes that the dust will fall away. This procedure should not be done with canned compressed air since the jets may be contaminated with oils or other solvents. The use of a blower is a reasonably safe procedure, but it is not totally risk free. The danger is that if the power shuts off during cleaning, the mirror and shutter will close potentially leading to severe damage. Ideally the camera should be attached to an external power source or at least have a fully charged battery.

 
Touchy-Feely
If after I have applied a vigorous blow there is still substantial amounts of dust on the sensor, I am faced with a dilemma. The next steps in cleaning are more vigorous, involve touching the anti-aliasing filter and can cause scratches or leave residues. I am very reluctant to risk damage to the sensor and I have to consider very carefully weather physically removing the remaining dust is worth the risk. I have only rarely resorted to the use of brushes and swabs and have never suffered a disaster, but I don't like pressing my luck. Most often I have decided to accept the requirement to remove dust splotches in post processing. Dust removal tools in Lightroom, Photoshop and other editing programs have improved to the point that there is less need to risk your sensor, but, if you are an adventurous sort, the internet contains many excellent reviews of the more invasive dust removal techniques.

• Cleaning Digital Cameras 
• Sensor Cleaning : Luminous Landscape 
• Canon sensor cleaning: remove dust in 4 steps

An Plan of Action

Use Levels Adjustment to Reveal Dust

My general approach is to do all I can to reduce the exposure to dust and minimize its effect. I use the automatic sensor cleaning and when necessary I carefully blast away with blower. In general I can manage the remaining dust with the use of Photoshop's Healing and Cloning brushes. 

Remove with Healing Brush

 
I usually use a Levels adjustment to darken the image, which reveals even the more subtleblotches. Dust spot removal is just part of my routine detailed inspection of my images and does not add significantly to my processing time. Both Lightroom and Photoshop have specialized spot removal tools, but I usually still stick to my careful manual approach.  I find that I have better control over the size of the brush and the source of the healing pixels.

Five Barns, Putney, Vermont : Cleaned Sky

Lightroom Spot Removal

More Foreground, Less Sky

Don't get me wrong, I still get annoyed by all those blemishes and when they get too prominent and refractory to ordinary cleaning methods, it is probably a good time to send the camera to the manufacturer for a thorough cleaning. It means having to fall back on my smaller "pocket" cameras, but it can be nice to be liberated for a couple of weeks from my massive beast. And, when the monster returns, it is nice to have a spanking clean camera with that lovely, new camera smell and no dust.


Jeffrey Newcomer
Partridgebrookreflections.com