Should you clean your lens?

by Nick Kelsh

posted Tuesday, March 3, 2015 at 2:13 PM EST

 
One ride in the back of a pickup truck on a dirt road and your lens could end up like this. It’s looks a lot like sandpaper, doesn’t it? And that exactly how that grit will behave if you rub it with cloth.

I hesitate to even discuss lens cleaning; I risk turning you into one of those lens cleaning fanatics simply by broaching the subject and that’s the last thing I want to do. I want you to leave your lens alone.

But the time will come when the build-up of daily life needs to be removed and you need to do it carefully. What you really want to protect is that purple, blue-greenish coating that’s on the surface of the lens that actually helps light pass through the glass to produce sharp, colorful images. You paid a lot of money for that coating so let’s take care of it.

Dirt on lenses comes in two categories. First, there’s grit. That’s dirt. If you rub it it behaves like sandpaper. Do not sand your lenses. Secondly, there’s grime. That’s grease and fingerprints. That will require some rubbing to remove it, but very little.

I use canned air to remove dirt. Canned air can be tricky—if you shake the can liquid will shoot out, so shaking canned air is to be avoided. My approach is to set the can of air on the table and not move it. Then I put the lens in front of the nozzle and move the lens around. I never shake or move the can. That removes most of the grit.

Grime is another animal. My policy is to simply breath on the lens to fog it and VERY LIGHTLY rub it with a high-quality optical cleaning cloth. If the grime doesn’t come off with that method I just leave it. A little bit of grime doesn’t make any difference to lens performance.

I remember an optical technician explaining it to me this way. A lens consists of several pieces of glass. They’re called elements. If you calculated the entire surface area of glass in your lens, the front and back elements— the ones you can actually touch— would actually constitute a small percentage of the entire surface area of your lens. So if you leave a bit of dirt and grime on those two elements, most of your lens is still factory clean. In other words, don’t sweat it.

 
The camera being used to take this picture, on the left, of me and my Creative Memories friend was beyond dirty and in direct sunlight. I could see the dirt on the lens glowing from ten feet away. We stopped the photo shoot, cleaned the lens and proceeded to take the picture on the right. When there’s and dirt and grime on your lens and it gets hit by direct sunlight, you’re going to get a foggy, low-contrast look. You will not, however, see individual bits of dust and dirt in your pictures. If you do, your image sensor inside the camera is dirty, and that’s a discussion for another day.

It’s also worth understanding when a dirty lens is really going to affect your pictures. If harsh sunlight is hitting the dirt and grime directly it will make your photograph look like it was taken through a bit of fog. You won’t see individual pieces of dust and dirt; they’re too close to the lens. They’re way out of focus. But they will register as a bit of bad weather. On the other hand, if you keep stray light off of a slightly dirty front element, it will behave like a perfectly clean lens.

The secret to having a clean lens is to never let it get dusty and dirty in the first place. The time to take care of your lens is when it’s new.

It will never be cleaner than when it’s right out-of-the-box. And that is the time to put a clear glass screw-on filter over it that keeps the lens permanently clean. (These filters are called UV or Skylight filters. They cost about twenty dollars.) It’s comforting to clean—and abuse— a filter knowing that your expensive optics are warm and dry and clean underneath. And the filter behaves like a little piece of armor that protects the front of your lens from dings and drops. Please put a filter on every lens you own.

(An exceptional educator and a world-class photographer, Nick Kelsh is the founder of How To Photograph Your Life, an excellent source of affordable photography training and tips. Nick’s courses can be conducted by yourself in your own time, or with feedback from Nick and your fellow students. If you appreciated this article and want to improve your photography, visit How to Photograph your Life and sign up for a course today!)