April 2010 - Digital Group Meeting - Sensor Cleaning

Meeting Notes March 2009 to 2018.
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spb
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Joined: Tue Mar 25, 2008 7:04 pm

April 2010 - Digital Group Meeting - Sensor Cleaning

Post by spb » Fri Apr 02, 2010 1:13 pm

The beginners subject tonight was PC Housekeeping, in which we covered filing, backups, security and routine maintenance. A couple of recommended applications are SyncBack Free which synchronises backup folders and Acronis True Image Home ($59) which creates an image of a disk for total restoration purposes. Microsoft Security Essentials (free) is proving to be an effective and virtually invisible protection against the more common threats.

DSLR SENSOR CLEANING

Digital SLRs are prone to contamination of the sensor and self-cleaning mechanisms are not a total answer. To check your sensor, take a picture of a white surface. Use Manual or Aperture Priority mode to set the minumum aperture. You may also need to switch to manual focus if the camera refuses to shoot such a featureless subject. To get access to the sensor, set the camera to sensor cleaning mode (for which you may need a fully charged battery). An illuminated loupe can help to inspect the sensor directly which is not as delicate as people fear and you are actually cleaning a glass filter, not the sensor itself.

Contamination may be dry eg dust, or wet eg atmospheric moisture particles. For dry particles a blower bulb is often recommended but I have found that this just re-distributes the muck from the mirror box and makes things worse. Some form of statically-charged soft brush is required and the Arctic Butterfly (£45) from Visible Dust is very popular. An alternative is a low-tack pad such as the Dust Aid products.

Wet contamination requires an alcohol swab such as those from Visible Dust. The important thing is not to use too much alcohol and not to rub the swab over the sensor repeatedly - one wipe per side only.

There are some good videos of sensor cleaning using various products on YouTube.

Compact cameras are not immune from particles on the sensor. In this case the only remedy is a service. For inexpensive cameras this may not be cost-effective and given that lens-mechanism faults are also common, I highly recommend buying from a retailer that includes an extended warranty of two or three years. I purchased a Canon G11 from Amazon recently and was amazed to find that they offered an additional two years warranty for only £20 which seems like a bargain for a pricey camera.

EXPOSE TO THE RIGHT

There has been much discussion recently about how to capture the maximum possibled detail in digital images. Although counter-intuitive it would appear that ensuring the camera histogram is as close to the right hand edge as possible (without actually going to the edge) ensures that a vast amount of highlight detail is not lost. Failing to use the top fifth of the histogram has the potential to lose half of all possible tonal values! Care must still be taken to avoid burn-out as shown by the flashing highlights camera display. There is an interesting explanation of this phenomenom at Luminous Landscapes . Although usually discussed in the context of RAW images, the same applies to JPGs as well.

The quality of the image on the back of the camera may suffer as a result of this technique but that is not a true guide to the final results that can be obtained by careful use of RAW conversion software. The image on the back of the camera should only be used as a guide to sharpness, composition and checking for erroneous camera settings!

This should not be taken as an endorsement of RAW image-taking. JPGs are totally acceptable for most purposes and I would never recommend RAW images for beginners. JPGs can suffer if the exposure is wrong but learning to control exposure is an essential skill for beginners to master.

TEE SHIRTS ETC!

I demonstrated a design project which was converted into Tee Shirts for a recent biking tour by Tee Shirts Etc! at Bovingdon. They did a good job at a very reasonable price of £13 each for a print on a good quality Fruit of the Loom tee shirt.

CURVES

Malcolm Cartledge recommended this plug-in for Photoshop Elements which adds a full Curves capability - one of the few significant tools missing from Elements in comparison to full Photoshop.

Cheers, Steve Brabner

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