If you're like me, the thought of touching, let alone fully cleaning your precious glass or even worse, your sensor, strikes fear into your heart. It's a skill every photographer should have, however. Learn how to do it safely here.
Lenses are slightly (only slightly) less scary to clean than camera sensors. After all, we've all likely cleaned a piece of glass in our lives, right? Glass is relatively strong and can tolerate a thing or two. On the other hand, I'm convinced sensors are made of tissue paper and snowflakes. So, let's start with the easier of the two.
There are two guiding principles you should always follow when cleaning camera equipment: only do what's necessary and always minimize actual contact with the equipment. A few years ago, I used to give my gear a thorough cleaning every month whether it needed it or not. I found that this actually introduced more problems: by touching my gear so much, I was actually introducing more potentially damaging particles into the environment than if I had just left it alone until it truly needed a cleaning. Furthermore, you should only touch the equipment as much as you actually need to; often, this equates to not touching it at all. A good rocket blower may be all you need most of the time.
Step One: Blow It Off
This is always how you should start when cleaning a lens. It minimizes contact to the point of no contact at all. Don't use your mouth; blowing on your lens orally can coat it with saliva or condensed water. Also, never use compressed air; the condensation issue is quite pronounced. Instead, get yourself a good rocket blower. I'm particularly fond of the Giottos Rocket Blower. Always give the blower a few puffs directed away from the lens first to clear out any particulates it may have gathered internally. Then, hold it as close as possible to the lens (to minimize blowing any debris in the air between the blower and the lens onto the glass) and blow across the surface.
Pro note: I also keep my blower stored in a plastic bag to avoid it accumulating any dust that might be thrown on the lens when I use it.
Step Two: Brush It Off
If there's still debris or smudges on your lens after you use a blower, move on to a brush. I highly recommend the Carson CS-20. Begin by using the bristle end (never touch the bristles with your fingers) and gently brush across the lens surface, using your wrist to twist it back and forth. Never jam the bristles across the surface in an attempt to dislodge particularly stubborn debris.
Step Three: Wash It Off
If blowing and brushing fails you (or if you have streaking on your glass), it's time to clean it using a cleaning solution and cloth. Before anything, be sure to remove as much debris as you can with the two aforementioned methods, lest you may end up grinding it into the glass. Personally, I'm a big fan of Zeiss microfiber cloths and cleaning solution. Be sure you are using a specialized microfiber cloth; the relatively coarse fibers of regular fabrics can scratch your optics. Always keep the cloth clean (store it in a plastic bag). If you launder it, avoid using fabric softener and give it a second rinse.
Spray the cleaner directly on the cloth (not the lens). Using light pressure, wipe in increasingly large circles outward from the center of the lens. If there is residual moisture, quickly flip the cloth over to the dry side and wipe in the same fashion; doing so before the cleaner evaporates will help to prevent streaking.
Clean filters in the exact same manner as lenses.
Should My Lens Always Have a Filter Attached?
A lot of people argue that a UV filter degrades image quality. I have only seen extremely specific situations in which a UV filter could slightly increase flaring and loss of contrast, but these are situations one almost never encounters. For me, personally, a high quality UV filter causes no perceptible loss in image quality and greatly increases the protection of the most vulnerable portion of the lens, the front element.
On the Go
When I'm out and about, I always carry a mini blower and pocket brush. In the rare event that something happens that absolutely requires an immediate cleaning, I recommend Zeiss Lens Wipes. Just as before, be sure to clear the lens of any debris before you start rubbing it and be sure not to touch the side of the wipe that is contacting the lens. Also, only resort to this if the blower and brush haven't provided a sufficient cleaning.
Cleaning the Mirror
Never clean the mirror with anything but air. The surface coating of the mirror is extremely fragile and will scratch much more easily than the surface of a lens or even the sensor itself. If, by some misfortune, the mirror absolutely must be cleaned, send the camera to the manufacturer. Remember that any dust on the mirror may be annoying, but it will not have any effect on image quality.
Cleaning the Sensor
Before you decide to clean your sensor, you should be sure that you actually need to. To do this, grab a piece of printer paper and a normal focal length lens (avoid wide angle lenses in particular). Stop down to f/16 or f/22 (not more) and select a shutter speed that allows you to use the base ISO of the camera. Handshake is not an issue here. Take a shot of the paper, bring the photo into Lightroom or your favorite RAW processor, then remove all saturation and increase the contrast. Any spots of dust or other particles should show in sharp relief. If you see particles, use mirror lockup mode or a very long shutter speed to displace the mirror while you use a blower to gently remove those particles. Only use those modes for using a blower and keep it out of the path of travel of the mirror. If your camera has a built-in sensor-cleaning mode that flips the mirror up until you choose to flip it back down, use that. Keep the camera facing down during this process and be sure not to use the blower at full strength.
If your sensor is particularly dirty (think 30 or more particles that don't come off with a blower), it might be time to give it a full cleaning. Patrick Hall has written an excellent article on how to clean your sensor.
Keeping your optics clean is essential to maximizing image quality. Nonetheless, you should never clean more than you absolutely have to. It's always best to minimize contact with any fragile camera gear. Following these directions can help to ensure clean optics while minimizing the risk of damage.