DSLR - Checking & cleaning Digital SLR Sensor Dust

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When stored, handled and used properly, a camera lens and photo gear in general can last a lifetime. Several things can go wrong when small things are ignored that become big issues over time - both the optical components and the mechanical aspects of your gear can be affected adversely, sometimes irreparably. Here's a quick review of some of the basics in camera care:

First off, a list of "Do's":
 - Keep a Skylight filter on the front element of your lens. It protects the glass from debris and scratches. The ring can absorb a light ding and be replaced if your camera "slips". A ding on the filter thread of the lens will require repair or worse. If you are shooting with high quality glass, use a nice quality filter. If you are shooting in challenging lighting and concerned with flare, you can always remove the filter for the shot and then replace it.
 - Keep your lenses clean and use proper lens cleaning equipment and technique.
 - Keep the lens cap on the front element at all times except when taking a photo. Keep both front and rear caps on your stored lenses.
 - Keep your lens and gear out of extreme temperatures and humidity. Do not leave photo gear in a car on really hot days. Some experts suggest storing your gear in a sealed plastic bag when bringing it back inside to warm up after being exposed to cold. This keeps condensation off the gear.
 - When storing your gear, do so at or near room temperature, in controlled low humidity and ensure it stays dry. If it is wet, towel dry and leave it out until moisture has had a chance to evaporate.
 - Use a camera strap. Loop it around your wrist before gripping the camera or keep it around your neck . If you drop the camera, the looped strap should save your gear from dealing with the more serious effects of gravity.
 - Always treat your camera and gear gently. Never force anything, whether it be a lens mount, filter thread or USB connection.
 - If you live in a tropical environment (high humidity), you should consider storing your gear with desiccant to assist in absorbing moisture.
 - Always take out the batteries prior to storing your gear. This includes the camera body, flashes and any accessories. Acid leakage has destroyed more than a few pieces of camera equipment.
 - With DSLRs, keep lens changes to a minimum and make your lens change quick. Hold the camera with the lens opening facing downward. This prevents dust from settling inside the mirror chamber. Change lenses while the camera is turned off. These steps will minimise dust contamination of the CCD/CMOS, a common problem.
 - Try not to change lenses in windy, sandy or salty environments, eg. the beach.

Now, the "Don't"s (pretty much the opposite of the above list)
 - Never allow your gear to get wet. Dry it immediately if it does, and allow it to air dry indoors prior to storing. There are "Rain Sleeve" type covers available online that are inexpensive and will cover your camera and lens while shooting in wet environments.
 - Never store it away wet. Metal can rust and seize parts; fungus can grow on glass and inside the lens.
 - Never store your gear in a way that items contact each other directly. Gear will scratch and wear when rubbing against each other inside a camera bag.
 - Never mishandle or treat your gear roughly.
 - Never take your gear to the beach...ok, you have to, but keep lens changes and exposure to heat, wind, sand and sea salt to a minimum. This stuff will wreak havoc with just about every aspect of your camera gear. Just one splash; a few drops of seawater will smoke off a digital camera. Trust me on that one....Sand grains will get just about everywhere and I don't mean just in your bathing suit. Sea salt can cause corrosion on metal and electrical contacts.
 - Never store your gear for long periods with the batteries installed.
 - Never use solvents on your gear, or commercial glass cleaners on your lenses. A lightly damp rag is usually sufficient. You can add a drop of dish soap to the rag to help cut grease from your hands. Use only lens cleaning solution and tissue/micro fibre on your lens glass, but first, use a blower brush to remove any grit.

Sensor Dust
DSLR's need special care to prevent dust contamination of the sensor. If you've downloaded photos and noticed small round dots all over your photos, particularly in the sky of your image, then you've got dust! You may notice it in only some pictures, because  it shows up more so when you are shooting with a smaller aperture.
You can reduce sensor contamination by doing the following:
 - Minimise lens changes (that is a tough one, after all, what is the point of having a single lens reflex camera?!)
 - Do not change your lens in a windy or dusty environment. As soon as you open up your camera, it is ripe for contamination. The beach, with sand and sea spray is the last place you should change a lens on any camera, nevermind your expensive DSLR. If there is no wind and no one is shaking out a beach towel nearby, I would take the chance and quickly change lenses to get the shot, though.
 - When changing lenses, point the camera towards the ground. Any dust and bits should then fall out of the camera rather than settle inside.
 - Ensure your rear element is free of dust and contamination prior to attaching it to your body during a lens change.
 - DO NOT leave your camera power ON while doing a lens change. Your sensor is a dust magnet when it is "charged" with the camera turned on - don't open up your camera with the dust magnet "ON"!  You might think your shutter (covering the sensor) will protect the sensor from dust and it does, right up until you press the release to take a picture. The sensor is then exposed and charged up, attracting any loose, floating dust particles that have entered your sensor chamber.
 - When shooting in particularly dusty environments, or when during a day doing multiple lens changes, clean your sensor as a part of your routine at the end of the day.

"How do I know if my sensor is clean?"
Chances are, if you are concerned about sensor dust, you've already found a blob or two (or more!) on your images.
As mentioned above, routine sensor cleaning is a good part of your routine camera maintenance.
Some DSLR users may notice a slight vibration emanating from your camera. This is the sensor shaking to remove dust from your camera's sensor. This is your first line of defence against sensor dust.
For more resistant dust, first blow out the mirror box with the camera off and lens removed - preferably in a wind free, dust free location. Use a good "rocket blower". We use Giotto's - you can search them out on eBay. Don't bother using one of those little lens cleaning blowers - they don't generate enough air flow to be effective. Some DSLRs have a "Sensor Cleaning" function in their submenus.Follow the instructions for initiating sensor cleaning mode (maybe review the section on cleaning in your camera manual beforehand). With the sensor exposed in cleaning mode, remove the lens for a second time and use a rocket blower to blast air over the sensor to remove stubborn dust. Turn the camera off to exit cleaning mode and immediately replace the lens.
To check your sensor for dust, the first thing to do is take a picture! Actually, you need to take a picture of a blank sheet of paper. Use your flash, with a stopped down (f/16, f/22) aperture and a fairly close focus lens. Try to fill the frame with the paper sheet so that all you get is a blank, white image. You may need to increase your flash setting to get a good exposure. You may need to manually focus due to the lack of contrast.
Download the image of the paper on to your monitor, and magnify to 100%. Review the entire image - you'll likely still see some dust spots. Larger dots (3-5mm) will be pretty obvious already on your regular picture images, but smaller dust spots may not show. If you've already detected dust in your regular images, performing this test will confirm the location of the dust and the also map out the degree of contamination. Remember, what you see on the image is flipped compared to the dust locations on your sensor. Left to right does not change orientation, but top to bottom is reversed.

"What do I do, now that I have dust on my sensor?"
As detailed above, non-contact sensor cleaning is very easy and safe if done properly. Work carefully and deliberately. You need a good bulb blower like a Giotto's (no brush attached) to generate a sizeable blast of air. The little silver dollar sized blower you got for blowing dust off your lens is not big enough. There are several blowers on the market that are bigger and more appropriate. Do not used "Canned Air" to blast your sensor as it contains propellant that will totally mess up your camera's insides.

Step by Step Proper Sensor Cleaning Procedure (a more detailed approach):
Step 1
In a well lit, dust free environment, preferably indoors, remove your lens from your DSLR (camera is turned off!) Point it towards the ground and while holding it so you can see up inside to the shutter plane, use your blower to squirt rapid blasts of air inside the mirror chamber, (taking care to not bump anything with the bulb tip!) then reattach your lens. You have just NOT cleaned your sensor. What you have done to this point is hopefully removed any contaminants from the mirror chamber. We use a bright LED lamp pointed upwards so that we have plenty of light and can visualise the inside of the camera and don't inadvertently get too close to the shutter or mirror.
Step 2
Now follow your camera's instructions (in the manual) for putting your camera into "cleaning" mode and follow these instructions to the letter. This process releases the shutter and exposes the sensor so that you can repeat the previous instruction step and blow air across the sensor, hopefully releasing any dust that is attached to the sensor. Ensure that the tip of the blower does not touch the sensor.
Step 3
Repeat the "paper test" and compare your new, hopefully cleaner image to the original test shot. If there is significant improvement in decreasing the amount and size of your dust contamination, you can now go take a picture of blue sky at f/22 and see if your original dust dots are gone from a "regular" photo. If your image is clean, then your sensor is clean enough. If you still see dust in your regular images, you'll have to repeat the cleaning process. Sometimes it can take a few attempts to be successful. Your serial "paper test" images will give you a reference map of whether you are making any progress in subsequent cleaning attempts. You'll never get all the dust off the sensor and even if you did, it would eventually re-accumulate, so only clean your sensor to the point that your photos are clean.

Sweeping and Cleaning
If after several attempts, there are dust spots that haven't moved, it is likely that these are firmly attached to the sensor.
To remove stubborn, or "glued on" dust particles you will need to "sweep" your sensor with a brush, and possibly "wipe" it with a moist pad. You can cause damage by scratching the glass filter that is in front of your sensor if you are not careful. Make sure my brush is blown clean prior to sweeping, and blow both the brush and the sensor after each attempt to clean. (Don't use the brush for anything else!) Repeat the "paper test" to check your progress. Because a brush does not have a static charge to attract dust, you will mostly move dust around the sensor, but sometimes this is enough, coupled with the blower, to dislodge stubborn particles.
If sweeping doesn't work, and you've still got dust blobs affixed to your sensor, it's time for a moist wipe. There are commercial products advertised on the internet and in camera stores for brushing and wiping your camera's sensor, including Visible Dust, Artic Butterfly and Sensor Swab. A quick google will send you off to read reviews of these products and others, their pricing etc. 
Apply a couple of swipes (gentle pressure) with it, then repeated with a dry swab to collect any moisture and finally some air blowing to remove any paper fibres can work wonders. Try a couple of swipes, enough to cover the surface area of the sensor once should suffice. Back to the "paper test" and you can check your work.
Again, remember that you won't get everything off the sensor - once you've got this far with your cleaning, try taking a photo of blue sky at f/22 and check your image for spots. If your image is clean, it's "mission accomplished".

Summary
Those are some of the more common sense things you can do to take care of your gear. We tend to tuck our camera stuff away for extended periods and a lot of nasty things can destroy gear while it sits in the closet! The worst environment for your camera gear includes moisture, warmth and darkness. You might not recognise your camera after it has sat in the closet for six months in those conditions. If you are lucky, the damage will be cosmetic only. Unfortunately, battery corrosion and fungus growth can cause permanent damage. And sensor dust can be frustrating. The last thing I want to do is "spot clone" a weeks' worth of vacation photos to get rid of dust spots! A little maintenance prior to or during your trip or next shooting session will reduce the post-processing work afterwards.

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