Lens Cap... Danger! #91

Lens Cap... Danger! #91

Many moons ago I read somewhere that you shouldn’t leave your lens in the sun. The suggestion was left without a real explanation as to why. I thought perhaps it was an issue of heat, but it never seemed reasonable to me because glass doesn’t melt until about 1400C! Metal on the other hand melts at 1300C and rubber melts at about 187C! Trust me if you are sitting anywhere that is 187C you have bigger issues to consider than the health of your camera equipment. So why is leaving your lens or camera in the sun an issue? Other than perhaps the electronics, this advice didn’t make sense to me. A couple of years ago I finally read in a manual that you should not leave your lens out in the sun without a lens cap on because of the potential of a fire. The manual suggested that at the right angle the sunlight would magnify the light onto a flammable surface and blaam! Your house burns down! Although this seemed possible it just didn’t seem probable. That is, until this year. I’ll start by saying that nothing burned down and my house is still standing. So relax folks.

Ok, so what happened? I was about 5 days into my trip Mexico and I was shooting with my 70-200mm lens and I noticed that my photos were completely foggy and the image I saw through the viewfinder of my DSLR also looked foggy. But there was no fog. It was the middle of the day and sunny without a cloud in the sky. I thought perhaps my LCD was dirty so I cleaned that. But then there was the viewfinder, but that was also clean. The front element of my lens was definitely clean. Even with that I cleaned everything again, but it still didn’t resolve my problem. At that point, I decided to dismount the lens. And wouldn’t you know it, the back element looked like someone blew smoke into it and there was a film evenly spread across the glass. I proceeded to clean the glass and it resolved my problem. This was really weird because I rarely ever have a dirty back element and even then there’s ever just a little bit of dust. And I had already been shooting with the lens for days. But on the other hand I thought nothing of it until I changed my lens and put the rear lens cap back on my lens. Low and behold, there was a small hole that had melted in my cap and it started from the inside. The fact of the matter is that I do not use front lens caps. As a result my front element is always in the open. The only thing I can think of is that while traveling around I left my bag open long enough for the sun to shine through the lens and it melted the cap. As it did so the smoke left a film on the rear element. So there it was, proof positive that it is not only possible but there is an actual measured probability of this happening. So from now on I will pay more attention to sun hitting my lens! Crazy right?