About two years ago, after running through a series of second-hand compact cameras, I went looking for a compact of my own. I’m not entirely sure what the requirements were – availability, mostly – but I ended up grabbing a Panasonic Lumix DMC-TZ80. One of the neat features about this camera is its whopping 30× zoom: 4.3–129 mm, or “24–720 mm” as the “35 mm equivalent”.[1] That makes it a pretty versatile unit, but that far end of the range ended up being more useful than I anticipated, because it turns out what I want to photograph …

Magnifying glasses operate on a pretty simple concept: when an object is within the focal length of a convex lens, a magnified ‘virtual’ image is produced, as demonstrated by simple ray optics:

… with just the slight problem that the magnified image is always further away. An object at the focal point produces an image that is literally infinitely big – but it’s also at an infinite distance. And that really doesn’t help; the moon is quite sizeable itself, but that won’t show you the dust on its surface.

Still, magnifying glasses certainly seem to have an effect – but …