Should you clean your sensor? Some vendors countenance only dust-off cleaning, through the use of reasonably gentle blasts of air, while condemning more serious scrubbing with swabs and cleaning fluids. Removing dust from a sensor is similar in some ways to cleaning the optical glass of a fine lens. At the same time, imagine that dust particles are tiny, rough-edged boulders that can scratch the glass if dragged carelessly across the dry surface.

Picture the lens wipes as potential havens for dust particles that can apply their own scratches to your lenses.Those measures often include protective UV or skylight filters that can be cleaned more cavalierly and discarded if they become scratched. If all else fails, the experienced photographer will clean a lens’ optical glass carefully and with reverence.

The filters that cover sensors tend to be fairly hard compared to optical glass. Cleaning a sensor that measures 24mm or less in one dimension within the tight confines behind the mirror can be trickier and require extra coordination. Finally, if your sensor’s filter becomes scratched through inept cleaning, you can’t simply remove it yourself and replace it with a new one.

• Air cleaning. This process involves squirting blasts of air inside your camera with the shutter locked open. This works well for dust that’s not clinging stubbornly to your sensor.
• Brushing. A soft, very fine brush is passed across the surface of the sensor’s filter, dislodging mildly persistent dust particles and sweeping them off the imager.
• Liquid cleaning. A soft swab dipped in a cleaning solution such as ethanol is used to wipe the sensor filter, removing more obstinate particles.

The first thing to do is to lock up your camera’s mirror so you can gain access to the sensor. Some vendors recommend locking up the mirror for cleaning only if a camera is powered by an AC adapter, rather than by a battery. A damaged mirror, sensor, or both can easily be the result if the mirror flips down before you’re finished.

In practice, my digital camera’s battery poops out less frequently than I experience brownouts and AC power blackouts.

The easiest way to protect your sensor from dust is to prevent it from entering your camera in the first place. Here are some steps you can take:

• Keep your camera clean. Avoid working in dusty areas if you can do so. Make sure you store your camera in a clean environment.
• When swapping lenses, use a blower or brush to dust off the rear lens mount of the replacement lens first, so you won’t be introducing dust into your camera simply by attaching a new, dusty lens. Do this before you remove the lens from your camera, and then avoid stirring up dust before making the exchange.
• Minimize the time your camera is lensless and exposed to dust. That means having your replacement lens ready and dusted off, and a place to set down the old lens as soon as it is removed, so you can quickly attach the new lens.
• Face the camera downward when the lens is detached so any dust in the mirror box will tend to fall away from the sensor. Turn your back to any breezes or sources of dust to minimize infiltration.
• Once you’ve attached the new lens, quickly put the end cap on the one you just removed to reduce the dust that might fall on it.
• From time to time, remove the lens while in a relatively dust-free environment and use a blower bulb (not compressed air or a vacuum hose) to clean out the mirror box area. A blower brush is generally safer than a can of compressed air, or a strong positive/negative airflow, which can tend to drive dust further into nooks and crannies.
• If you’re embarking on an important shooting session, it’s a good idea to clean your sensor now using the suggestions you’ll find below, rather than coming home with hundreds or thousands of images with dust spots caused by flecks that were sitting on your sensor before you even started.

To save battery power, your dSLR doesn’t start to focus the lens until you partially depress the shutter release. But, autofocus isn’t some mindless beast out there snapping your pictures in and out of focus with no feedback from you after you press that button.

• Continuous autofocus. The chief drawbacks of this system are that it’s possible to take an out-of-focus picture if your subject is moving faster than the focus mechanism can follow, it uses more power, and it makes a distracting noise.
• Single autofocus. In this mode, once you begin to press the shutter release, focus is set once, and remains at that setting until the button is depressed, taking the picture, or you release the shutter button without taking a shot.
• Dynamic focus area. Because your dSLR has more than one focus sensor checking your frame, it may shift among them as focus is calculated. With dynamic area autofocus, the camera may automatically switch from using one sensor to a different sensor if it detects subject motion.
• User selected focus area. You switch from one focus area to another using the cursor pad.
• Nearest subject. In this mode, the autofocus system looks for the subject matter that’s closest to the camera, no matter where it is located in the frame, and focuses on that.
• Focus lock. Your digital SLR has a focus-locking button that lets you fix the focus at the current point until you take a picture.
• Focus override. Macro lock/lockout. Some cameras and lenses have a provision for locking the lens into macro position so focus can be achieved only within the narrower close-up range. Or, you might find a macro lockout feature, which keeps the autofocus mechanism from trying to focus closer than a given distance.
• Autofocus assist lamp. This is an optional feature that can improve autofocus operation in low-light situations.