Weekend Thoughts on the Important Subject of Lens Caps
Despite the important purpose they serve by protecting glass elements, we're usually in a hurry both to take lens caps off in order to shoot and to put them back on when done. We treat lenses as being important but not really lens caps. It's time to give these small but important items proper consideration.
The primary purpose of a lens cap is obviously to protect the lens elements, but protect them from what, and when? I've made my views known before on using clear filters to protect a lens when you are using it, but suffice it to say the use of lens caps for protection is much more universally agreed upon than the use of so called "protective" filters. This is interesting since such filters stay on a lens all the time but a lens cap only protects the lens when not in use. You have to take the caps off to use a lens. And much of the time when a lens isn't being used it's just sitting there, seemingly less likely to get damaged than when being used. Perhaps an anomaly that would go unnoticed by most, but this consensus of opinion really does speak to the usefulness of lens caps for protecting a lens. Of course when you do take the cap off, be sure to use a lens hood whenever possible. Not only does a hood help reduce glare and ghosting problems it can also be help prevent mishaps caused by an exposed front element glass hanging out there.
Lenses can potentially get dropped or bumped any time, but the main enemy most of us want to keep away from our lenses when they're not in use is common, everyday dust. Dust doesn't seem like much of a danger but all I have to do is look around my house to see how it can pile up when you aren't looking. Dust is sneaky and clever, finding its way into unexpected places unless you take steps to prevent it. Not only is it difficult to take a sharp picture through a layer of dust, it's quite possible to scratch a lens element by rubbing too forcefully when cleaning a lens with dust on it. Dust acts as an abrasive. Your best bet is to avoid getting dust on the glass in the first place.
To be effective at protecting against dust, a cap needs to fit its mated lens snuggly and not be liable to pop off at the slightest provocation. Spills and stains can also cause problems. It's surprising how easy it is to get a fingerprint on a front glass element when picking up a lens with no cap on it. I hate reaching for a lens in my camera bag and finding that the cap has come off in transit.
In my experience a lot of third party lenses come with extremely cheap lens caps. There are exceptions but cheap lenses almost invariably mean cheap caps. I have a couple of the newer Sigma "ART" lenses with nice caps, but these lenses generally cost as much as name brand Nikon or Cannon equivalents so they don't contradict my "cheap lens, cheap cap" rule of thumb. Cheap front caps are often too thin to provide much gripping surface to hold them on. And cheap rear caps are often not manufactured to fine enough tolerances to screw on smoothly and not come off until I want them to.
The best front lens caps I know of are the current "center pinch" Nikon caps. The older "side pinch" ones stayed on just as well, but they were sometimes difficult to remove when wearing gloves in cold weather. Reaching into a lens hood to remove one of the old caps was difficult even without gloves. The new caps are a definite improvement. If you're still using any of the old style front caps I'd recommend spending a few bucks to buy replacement new style caps. Just be careful of counterfeits. It's remarkably common for people on eBay and elsewhere to be selling fake Nikon lens caps. I used to know some Canon shooters who buy Nikon front caps for their Canon lenses which is a testament to how good they are. One Canon guy I knew though sticks black tape over the Nikon logo so people don't find out. It's a complicated world we live in I guess. Canon did recently redesign their own front caps so this use of the competitor's caps seems less prevalent today than it was a couple of years ago.
One Nikon shooter I know these days defaces his lens caps for a different reason. He paints them with fluorescent orange spray paint to make them easier to find if he drops one. I guess a black lens cap can be hard to spot, but thus far the only cap I've ever lost was one that blew away in a gust when I set it temporarily on a bridge railing. There wasn't any wind at all, or so I thought, at least not until that fateful moment. Sometimes the unexpected can and does happen, but no amount of fluorescent paint was going to allow me to retrieve that cap from the streambed a hundred feet below that bridge. As such, my Nikon caps are still their original color.
Another interesting lens cap marking trend I've observed has to do with which cap goes with which lens. Some photographers label their lens caps with the focal length or some other designation for each of their lenses. This seems to be intended to improve the ease with which they can quickly find the lens they are looking for in their bag but I've yet to have much difficulty in this regard myself. I figure if I have two lenses so similar I can't tell them apart I probably don't need to carry both. The lenses themselves already come from the manufacturer with appropriate markings. There's actually a line of rear lens caps for both Canon and Nikon called LensBling made by BlackRapid that feature preprinted focal length markings. We live in a complicated world indeed.
Personally, I want all my caps to be interchangeable. I like that most Nikon "pro" lenses feature a consistent 77mm thread size so the front cap from one can fit on the front of another. With only a few exceptions, Nikon rear caps are already universally interchangeable since they all fit the same Nikon bayonet mount. I don't need to put the right cap back on the right lens; I only need to worry about making sure a cap is back on each since they're all the same. Nikon teleconverter caps have a more mixed history though. It was annoyingly possible to get an older Nikon body cap stuck on a teleconverter if you mixed up a nearly-but-not-entirely identical BF-1A with a BF-3 cap. Once stuck, it was almost impossible to remove so I did mark my teleconverter caps to keep things straight. Thankfully, the newer BF-1B incarnation fits both just fine. I bought new caps to replace all my older body caps so I can't get things stuck in the future.
If you really don't want to worry about your front lens caps coming off by accident there are always screw on caps. Most lenses have front filter threads that also accept screw on caps but I don't view this as a viable option in general. It would just be too difficult to screw the caps off and on when lighting conditions or my subject is changing rapidly. There are also push on lens caps, but they rarely fit properly without being either too lose or too tight. Years ago I did find a great Contax push on cap that perfectly fit the front of the old Nikon 77mm polarizer. The filter itself was an odd front size so it was hard to find any cap that would fit of any type. Before I found the Contax cap I had already tried every type of Tupperware and Pringles potato chip can caps I could think of. Nikon themselves sold the filter in a big box with no thought to a cap whatsoever.
Once you take a lens cap off, the question arises what to do with it. Numerous companies sell "leashes" to tether a cap to the lens it came off of, allowing it to dangle freely from a cord around the lens body as you shoot. I rarely see anyone with much experience using these, perhaps because of how silly they look. I just drop my caps back in the camera bag or stick them in my pocket. I did have one cap that was somehow lost for over a year and magically reappeared one day. I still don't know which flap or divider it must have been hidden under or behind for that long but I was glad to have it back. I always carry a spare of each cap with me just in case and had bought a new spare when I got back from that trip. Once the wayward cap did reappear I had a second spare. Just make sure that before you put a cap back on your lens that it's clean. Putting a dirty lens cap on your lens can result in a dirty lens.
Some photojournalists dispense completely with using lens caps, even viewing their naked lenses as a badge of honor. Going sans-cap makes it that much easier to quickly change lenses I suppose, and if newsprint is your standard for resolution dust isn't any more of a concern that would be a few scratches. Most of us like the protection afforded by lens caps which makes it all the more curious why most cell phone cameras don't have caps. With the high megapixel counts in current mobile phones it's getting quite possible to take serious pictures with a phone camera so it would seem inevitable that users would be concerned about keeping the lens clean. But right now you're on your own. I rarely see someone cleaning the camera lens on their phone before taking pictures with it. Again with the complicated world I suppose.
Lens caps may be small items that are easily viewed as necessary evils or an afterthought but they really are worth paying attention to and giving some thought to. Your lenses and your images will thank you.