It's Lens Cleaning Time
Having taken a look at sensor cleaning last week, it would be remiss of me not to also address the topic of lens cleaning. CCD and CMOS sensor cleaning is an important topic for digital shooters, but clean lenses are necessary equipment for all photographers, whether their preferred medium be digital or film.
The best way to clean your lenses is to prevent them from getting dirty in the first place. It may sound like I'm ignoring the issue, but I'm not. With proper care, your lenses will need cleaning much less often. The best defense is a strong offense, so to speak. When you aren't using a lens, be sure it has a cap over both the front and rear elements. Even when it's mounted to your camera, keep the font lens cap on it when you're just walking around and not actively shooting. Use a lens hood too. Not only will this help to protect the lens, it will prevent it from accidentally brushing up against something and getting dirty. When I'm working quickly, I occasionally do swap lenses without putting the caps back on, but when I do, they go in a clean camera bag, and are never left for very long on their own. Using a rear lens cap religiously will also help keep dust off your sensor. Your camera is basically just a box and once inside, dust can fall where it wants to.
When shooting, and particularly when changing lenses, be careful not to put your fingers on the front element. While I do use "protective" filters when shooting around salt water or blowing sand, I can not advocate their use to help with keeping your front element clean. The logic of using them for this totally escapes me in fact. Rather than getting fingerprints on the front element, those who advocate this would have you get smudges on your filter instead. Which you still have to shoot through to take pictures. How would that help any?
You might think you can scrupulously clean the front element of your lens along with the back side of your filter, then screw the filter on to hermetically seal things, leaving only the font of your filter susceptible to fingerprints, but this isn't really practical. If you ever want to use a polarizer or any other filter, you'd either have to remove that "protective" filter, or stack filters and risk vignetting and increased chance of lens flare. Granted, if you ruin a filter by over-cleaning it, you're not out much, but wouldn't it make more sense to do what you can to keep your lenses clean, and learn how to properly clean it when you do need to? If you agree, read on.
If you manage to get just a few specs of dust on your lens, they aren't likely to have any impact on the images you shoot. Wherever you focus your lens, the front element is certain to be far outside your depth of field. When shooting into the sun, excessive dust can cause flare spots though, so don't ignore dust completely. Fingerprints or other smudges can lessen image sharpness but are not difficult to prevent. As mentioned already, keep your fingers off the front element. Try to keep your hands clean too, just in case.
No matter how careful you are, sooner or later you will need to clean your lens.
First, make sure you don't have any dust or other particles on the lens surface. If you are unsure, use a blower or soft brush. The standard photographic blower-bulb-brush gizmo can work well. Every camera store will sell you one for a few bucks, but this is not an area to skimp. Get a good one. Don't use canned air since the propellant might come out, leaving a sticky mess on your lens. No sense making your situation any worse than necessary.
Now you are ready to deal with any smudges or fingerprints. Assuming you haven't been eating fried chicken while using your camera, there's no need to break out the nasty chemical solvents and steel wool pads. To safely and easily remove most smudges, simply use your breath. Breathe hard on the lens surface to fog it and wipe with a clean microfiber cloth. Be sure to wipe, not rub. You do not want to use increased pressure to deal with spots that resists your initial efforts. If at first you don't succeed though, try, try again. You'll be surprised at how well this simple method will work. I have a bunch of microfiber cloths, but prefer ones that have a satin sheen to them. They seem to be softer than other types. Keep your microfiber cloth clean by washing it if it becomes soiled. Hand washing is best, but you certainly can machine wash if you want. Do not use fabric softener.
If you did somehow get grease or other uncooperative substances on your lens, shame on you. You probably still do want to clean it off though, so you will need something stronger than just your breath.
You can buy any number of products purporting to be lens cleaner. Most are best left on the camera store's shelves as they are either little more than water or worse yet, strong enough to possibly damage the coatings on your lens. One I have found that work well and is safe is Formula MC, although I am sure there are others. This is another item you don't want to skimp on, so don't buy the first $1.99 bottle you find at your local camera store. Make sure you don't get one designed as an anti-fog cleaner either as they will leave a fine residue on your lens. Many eyeglasses cleaners fall into this category, so look for one specifically designed for camera lenses and other coated optics. A small bottle of quality lens cleaner will last you a long time and still cost little more than the cheap stuff. Buy a new bottle every few years anyway to retain its purity.
You will also need lens cleaning tissue, but again, don't just pick up the first thing you come across. Cheap lens tissue can scratch lenses, so invest in some better quality stuff. For ultimate quality, go with something like Pec-Pads. Yes, you can get all the items I've mentioned as a kit from most camera stores, but I would advise against doing so. I have yet to see such a kit that didn't skimp on at least one component. Keep all your lens cleaning supplies clean themselves by storing them in a plastic bag inside your camera bag.
To use lens cleaner, apply a couple of drops to your lens tissue, then wipe the lens surface with it. Use a rotary motion, starting from the center of the lens and working your way out. Clean the edge near the filter ring last. Don't wipe with a dry tissue as this can increase the chances of scratching. Don't use more liquid than necessary as this will increase the chances of leaving a hazy film behind. Don't apply the liquid directly to the lens surface either to prevent the possibility of it running down and getting inside the lens. Always apply the cleaner to the tissue and then clean. And remember, wipe, don't rub.
For truly stubborn grease spots, substitute R-O-R (short for "Residual Oil Remover") for your usual lens cleaner. This stuff will get off most anything, but don't use it unless you need to. As a rule of thumb, use the least drastic method that will work for the situation at hand. After cleaning with R-O-R (or some other lens cleaning fluids), you would do well to clean again with your breath and a microfiber cloth. This will take care of any haze remaining on the lens from using the fluid.
The biggest mistake most people make is over-cleaning their lenses. Cleaning occasionally as needed is good advice; excessive cleaning to the point of being afraid to use your lens is a tad obsessive. The surest way to damage your lens is to over-clean it or use too much pressure when cleaning it. The coatings used on modern lenses help minimize flare and ghosting, but are not indestructible. As mentioned, a few specs of dust are not a problem, so only clean when you really need to and your lenses will serve you well for a long, long time.