Sensor Hygiene
Hairs, out of focus blobs and small specks of dust dotting your pristine blue skies – these are all things that your client does not want to see.
Dust on negatives and transparencies has always been an issue, but the advent of digital capture has bought it to the fore as one of the most irritating by-products of the modern photographic age.
Sensor dust can be a big deal, but some simple tools can deal with the problem effectively making hours with the cloning and spotting tool once again a thing of the past.
The term ‘dust’ is a generic term for a range of sensor contaminants from atmospheric particles through to animal hairs; particles of dried lubricant; plastic from body caps and, most significantly, shavings of brass from the lens mount.
These contaminants affect not the sensor itself, but the low pass filter that covers the sensor on all Canon DSLR cameras.
Electron microscope image of contaminant sticking to the sensor glass.
To deal with these various problems there is a range of solutions.
Preventative strategies
Before dealing with methods of cleaning, it is worth mentioning a few ways of avoiding the problem in the first place.
- When changing lenses, always turn the camera off to ensure the sensor is not ‘charged’.
- Replace camera body caps with the later, non-shiny type - they are less prone to generate dust in the camera. All new cameras from the new Mk III / Mk IIN / 5D / 30D / 400D onwards have been supplied with these as standard.
- Keep the camera internals clean – Dry/Wet DSLR sensor cleaning.
Solutions
Giottos Rocket-Air blower.
The main ways of dealing with sensor spots and to help prevent them in the first place are as follows:
Mini-Vacuum:
The Mini-Vac has a similar purpose to that of the cotton bud. Make sure you do not make contact with the sensor
as there is a high probability of damage, but it can remove small particles in the mirror box area of the
camera.
Air Blower:
One of the most common methods of light sensor cleaning is with blown air or gas, intended to remove light
contamination from the sensor’s cover glass. The old bulb-type blowers work well for light contamination
and modern variants such as Giottos Rocket-Air provide more power.
Air blowers also provide a safer alternative to the popular but risky cans of compressed or ‘canned air’. These can be dangerous as an oily residue can often be sprayed directly onto the sensor.
Many people swear by compressed air cans and certain brands claim to be residue free, but reports of sensor
contamination persist. Perhaps these are best avoided.
Sensor Brush
the Sensor Brush in its various designs from VisibleDust has become one of the most favoured products for sensor cleaning.
The technology is a spin-off from the medical industry and is based around very precisely formed brush filaments. When charged they attract dust from the sensor. When blown with compressed air or spun they allow particles to pass through them preventing the particles being dragged over the sensor therefore avoiding scratches.
Life Size detail of the filaments on the Arctic Butterfly.
It is very important to stress here that these are not normal brushes. The filaments are produced to very strict tolerances and brushes are individually inspected under a microscope before shipping. Trying to use an artist’s paintbrush will not work. There are many tales of scratches caused by paintbrushes.
Although similar to the naked eye, paint brush filaments are formed from natural materials and have sharp edges that scratch the delicate glass of the sensor cover. Additionally, they frequently contain a binder material that can cause contamination.
The original idea was that canned air was blown through the filaments to make them attract dust particles. For reasons outlined above, this rendered them vulnerable to contamination by the propellants in the can.
The solution was the beautifully named Arctic Butterfly, a sensor brush with a battery powered spinning device to charge the fibres and to dislodge any existing dust particles before use.
Wet Sensor Cleaning:
Generally, if your sensor is dirty, it is because there is a build up of dust on the low pass filter. On rare
occasions, the problem can be caused by moisture build up or a smear from the chamber lubricants. To heighten
this problem, dust sometimes gets in the mix and binds to the filter in a very stubborn fashion.
- swabs
At this point it becomes necessary to use a sensor cleaning swab with a specialist cleaning solution to wet clean the cover glass. This is the main process that Canon themselves use in their service centres for cleaning. It is extremely effective, but sometimes not necessary for simple dust contamination.
Rule of thumb
If there is a smear, carry out a wet cleaning then a dry cleaning, otherwise, just do a dry.
Conclusion
Canon is making great strides forward, especially on the EOS 400D and EOS-1D MarkIII, in its attempts to remove the problem of dust. Doubtless this will appear in other models in the future, but for the moment, the issue is something that photographers need to address.
Currently, the technology solution does not deal with liquid or more stubborn contamination, so sensor cleaning swabs and sensor brushes are likely to have a place in the photographer’s tool kit for some time to come.