How high is the light gathering power of a fast lens? High enough to light a cigarette!

You’ve probably heard that objects made of glass can cause wildfires, which is why you should not throw them away or leave them behind in the outdoors. However, according to Wikipedia not all glass objects are equally dangerous. Supposedly glass bottles and pieces of broken glass are relatively harmless in this regard, because unlike magnifiers, eyeglasses and camera lenses, they do not possess the light gathering power high enough to ignite dry grass and foliage. What this means for us photographers, is that we shouldn’t put our equipment somewhere, where it would be exposed to intense sunlight for lengthy periods of time. As you can see in the video I’ve embedded below, in the best case scenario someone could use it to light a cigarette. In the worst case scenario it could lead to severe fire damage, in which case one could count oneself lucky, if only the shutter curtain or the sensor – should the camera only have an electronic shutter – bites the dust. 😉

One bit of additional info: the lens, which you see in the video, is an old Carl Zeiss Planar T* 2/45 for the Contax G mount, which, having an aperture value of f/2, isn’t one of the fastest standard primes. However, if such a lens, with a measly aperture radius of only 22.5 mm, can gather that much light and produce that kind of heat, you can certainly imagine what an 85/1.4, with its 60.7 mm aperture radius could do.