Wednesday, 11 April 2007

Out, damned spot! - sensor dust (part 2)


You can spend quite a bit of money on products to clean your sensor. But when considering a large purchase bear in mind that in a very few years sensor dust may no longer be an issue on new cameras. Several current cameras have anti-dust measures built in, but a recent test on "PixInfo.com" suggested that most of them aren't terribly effective, although anecdotal evidence indicates that they may do better in "real world" conditions. It seems that this is an area where further development is needed. However, the manufacturers do seem to have dust removal in their sights and I would think the problem to be largely dealt with in the next few model updates. My point is just that dust removal equipment should not be viewed as a long term investment (but then by that logic digital cameras can't either).

As I mentioned in my last piece, the dust is not on the sensor, but a glass filter a little distance in front of the sensor, so when I talk about cleaning the sensor you understand that it is really this piece of glass that is being cleaned. OK. To the job at hand. First, some things not to use - under no circumstances use canned air directly on the sensor glass. I heard of someone who used such a can, and the nozzle came off and projected itself towards the sensor with expensive consequences (this will not be covered under your warranty, mainly because all the camera manufacturers tell you not to do it). Nor should you use CO2 blowers. Both of these may contain contaminants which will likely stick to your sensor. Lastly, don't use anything that will come into contact with the sensor that you use on anything else - just common sense really.

How do you test weather the sensor needs to be cleaned. A shot of a white evenly lit surface will tell you (I use a light box, but a plain sky or wall will do). Remember that the shot is of the sensor dust, so you don't have to hold the camera particularly still even at long exposures. Use a long lens stopped down to it's smallest aperture, and focus manually to throw your white surface out of focus so that you don't see any texture. Overexpose by a stop and a half and you should be able to see the dust clearly on the computer monitor, particularly if you increase contrast. Don't panic if it looks bad. You never shoot like that do you (You do? OK. Panic then). You are unlikely to get it looking perfect, but if you have the sort of spots that you can see in normal photographs then you are clearly looking for a marked improvement.

Quite recently Delkin announced a sensor viewer to give you an enlarged and illuminated view of the sensor and it's dust, and reports (one such here) suggest that it works quite well.

The first tool that everyone should have is a bulb blower. There is plenty of choice, but the one I use it the Giottos Rocket (large size), and it seems to be generally well regarded. I have no reason to disagree. This is the only method of DIY cleaning that Canon recommends.

If that doesn't work I use a "Visible Dust" brush. The brush has nylon bristles and is statically charged with compressed air. The static charge lifts dust from the sensor surface. This will work most of the time if the blower doesn't, but there are times when the particles are stuck or contaminated with something like grease (most likely on new cameras). An alternative to the brush method is the vacuum system used in the "Green Clean" produce. I haven't tried this, as it wasn't available when I bought my sensor brushes.

Where the brush doesn't work, wet and/or dry swabs are needed. There are many on the market but I have been using the ones produced in the UK by "Intemos". The same swab can be used either wet or dry, and I have found them to work well. Swabs are really the only method to use if there are greasy smears on the glass, because the cleaning fluid is a de-greaser. Do not over-wet the swabs otherwise you will be left with smears that then need to be removed.

As I have said, there are several methods, and you make your choice. However, most of these methods are not all things to all sensors. For instance if you start with a blower you may find that you can't get everything off. You might try a brush and find that some of the dust had grease on it so you now have to remove the smear (and clean the grease off the brush). What I am saying it that you will probably need several tools for different severity of dust, trying the simplest first (blower) and working towards the most severe (probably swabs) as the need arises - or as the severity of the problem rises.

Lastly, and as something of an afterthought, there is one other method of cleaning the sensor. You could send/take it to someone else to do. Some shops will do this (I heard of one charging about £200 - someone has a sense of humour) and of course the manufacturer of your camera. Either way this is not cheap, you will probably be without your camera for a number of days (Canon have just quoted me £30 inc. VAT to clean a 20D and £50 for a 5D and say it takes about a week) and there is no guarantee that the sensor will be spotless when it returns - in fact it's quite likely that it won't be. Let's hope that the camera makers get in-camera dust removal sorted sooner rather than later.

Some extra reading - www.cleaningdigitalcameras.com/ - Several links at top right - don't miss, also on Rob Galbraith's site and something from Bob Atkins.

Image: Isle of Wight, December 2006

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