The first question most people ask when shopping for a new lens is “Is it sharp?”, yet if you were to pop the lens cap off that new lens a month down the line there’s a 50-50 chance you’ll find dust and a fingerprint or two on it. And if it’s not on the lens, there’s a 50-50 chance there’s dust or a fingerprint or two on the “protective filter,” which was purchased to keep dust and fingerprints off that new lens. And that’s on a DSLR.
If it’s a point-and-shoot camera, there’s even a greater chance of dust or fingerprints on the lens because when you turn the camera off, the lens usually slips behind little louver blades that A) protect the lens, and B) hide the fact there’s dust or a fingerprint on the lens.
Checking your lens for dust and smudges is something you should do on a regular basis, not only to ensure you’re getting the sharpest possible pictures, but also because a fingerprint or alien smudge left to “ripen” can cause permanent damage to the lens coatings. Keeping your lenses clean isn’t rocket science, but nonetheless, is a chore that should be performed carefully, thoughtfully and with the proper tools and techniques.
Dust and smudges on the front element of your lens (or your filter) are the easiest to spot because they’re front and center. While dust and smudges on the front element can diminish sharpness and contrast levels, you lose greater levels of sharpness and contrast when you have dust or smudges on the rear lens element because that’s the one that ultimately projects your image onto the camera’s sensor (or film). If your “projector lens” isn’t clean, your pictures won’t be sharp as they can be.
The surface of your camera’s lens has special coatings designed to maximize contrast, color saturation and color fidelity as well as minimize flare. These coatings can be scratched easily, and as such, when cleaning your lens it’s always a good idea to keep things simple. If dust or loose grit is the only villain, the best way to get rid of it is to gently brush the surface of the lens with a soft, camel-hair brush or give it a few blasts of air using a bulb-style air blower. Avoid using pressurized canned air. Avoid grinding grit into the lens surface with a cleaning cloth.
Smudges and fingerprints take a bit more effort, and here too, you should be as gentle as possible. Start by taking a soft micro-fiber cloth or a piece of lens tissue (folded, not bunched up), breathe onto the lens surface (never dry-clean a lens) and gently wipe the lens surface in a circular motion. Repeat if needed using a fresh piece of lens tissue or clean portion of the micro fiber cloth. If this doesn’t work, try dampening the tissue or cloth with a few drops of methanol (wood alcohol) or alcohol based lens-cleaning fluid and try again by gently wiping the lens in a circular motion.
Alcohol or lens-cleaning fluid should never be applied directly onto the lens surface. Doing so can possibly harm the lens coatings and/or compromise the adhesives that hold the lens elements in place.
If you’re out on a shoot and need to clean dust or smudges off your lens, and do not have a micro-fiber cloth or lens tissue with you, a cotton t-shirt or similar cotton-based material (preferably old and not freshly starched) should do the job equally well. What you never want to use is facial tissue, paper towels, polyester-based material, or any type of coarse or abrasive fabric or paper surface.
If the above procedures fail to do the job, or if gritty particles that can scratch the lens coatings are embedded in the smudge, you’d be wise to have a qualified technician address the problem.
If you can see a few bits of dust floating around between your lens’s inner elements, they’re not worth fretting over, as they will have little if any visible impact on the sharpness levels of your photographs, and are certainly not worth the time, trouble, or expense of having the lens taken apart, cleaned and reassembled.
A common misconception about dust is that you can see it in your camera’s viewfinder. The truth is the specs of dust you see in your viewfinder are not on your lens, but on your camera’s mirror. These dust marks, as distracting as they may be, do not affect your picture quality. Now before you take your lens off and try to clean your mirror, be advised the mirror in your camera is a surface-coated mirror finish, which can be permanently scratched with little effort on your part. Never, ever try blasting dust off with canned air, because you’ll most likely pit or scar the mirrored coating, or even blow the mirror off its hinges altogether.
The most drastic action you should take is to try removing the dust particles by gently blowing them off with a bulb-type air blower. If this doesn’t do the trick, bring the camera to a trained technician or simply live with it because as noted above, dust on the mirror is annoying, but will not affect your picture quality.
Dust marks on your image files―specifically, blurry smudge-like marks that appear repeatedly on the same portions of all of your image files―are caused by dust on your camera’s imaging sensor. Here too, the most drastic and least invasive action you should try on your own is to remove the lens, set your camera to the mirror-lock position, and gently blow it off with a bulb-style air blower while holding the camera face down. If this does not work, it’s recommended that you have a trained technician clean your camera’s sensor. And just as you should never blast your mirror with canned air, the same goes for your camera’s imaging sensor.