Dirty Lens Caps Mean Dirty Lenses
I've written before about keeping your lenses clean and even about keeping your camera bag clean. It occurs to me though that there is something else paying attention to in your cleaning regimen: your lens caps.
In the heat of the moment when working a subject under rapidly changing light, you might actually have the caps off a couple of lenses so you can switch back and forth quickly, but this is the exception rather than the rule. Most of the time, each of your lenses should be safely protected with caps, front and rear when not in use.
But where do you put the caps for the lens (or lenses) you are using? You might put them in your pocket for safe keeping. Or you might just drop them in your camera bag. Hopefully you don't drop them on the ground very often, but it could happen on occasion. Where ever you put them though, they can pick up dust and dirt. And that dust and dirt can get transferred to your expensive lens once you put those caps back on it. And we all know how much fun that can be to clean.
But it gets worse. Dust that gets transferred to a lens from its rear lens cap ends up on the lens flange, or perhaps even falls into the back of the lens. Either way, that dust can eventually find its way to your sensor. And that can be even more fun to clean off.
There aren't any perfect answers since dust and dirt are facts of life, especially when shooting outdoors. But it is worth considering the problem and taking reasonable measures to limit its impact.
When returning from a trip, or sometimes even at the end of each day if conditions warrant, I take some time out to clean each of my lens caps. I also wipe off the bayonet mount flange to catch anything that might have landed there. I figure anything I can catch by doing so is that much less I may have to clean up somewhere else later.
Update 12/04/2007 - Some readers have suggested using "cap-keepers" — essentially elastic strings that fasten to your lens cap on one end and the camera body (or lens) on the other. I suppose some people do use these things, but I've personally always found them more than a bit annoying since they leave your cap hanging out there, swinging around while you try to work. To each his own though, I suppose....
Update 12/06/2007 - Aother idea from travel photographer Nevada Wier, by way of reader PS: coat the inside of your lens caps with double-sided tape so that anything that does get in will get caught. This sounds like it has potential, but I'm going to have to think about it more before trying it. While it might perform as advertised, I'd be afraid that it might also serve as a magnet to actually attract more dirt and dust when the cap is off. It seems as if you'd need to carefully store your caps in a plastic bag when they weren't tightly on a lens.