I always wondered how people could justify buying an expensive macro lens for occasional shooting but a recent reddit post made me realize that you can get the same kind of macro effect by inverting a normal camera lens! The way that a normal lens works is that it focuses light from a scene through a series of concave and convex lenses to a small area on the camera’s sensor. The curvature of the lenses vary depending on the focal length of the lens, which also explains why a 20mm lens is wider than a 50mm lens. When you invert the lens (put it backwards), the opposite effect happens and light that comes in the back end of the lens (like in this picture) is now focused at a distance that the sensor would normally be (on my camera it’s about one focal length away).

A magnified view of an Alaska quarter from an inverted 20mm lens

Crunching a few numbers, the head of the bear is about 0.635cm on the quarter, and in the picture it’s about 1582px out of the full 4000px at the large size. That’s about 39.55% of the frame and since the micro four thirds sensor is roughly 18mm x 13.5mm, this translates to about 7.12mm in actual size or a magnification of roughly 1:11.2!

This isn’t too shabby for a make-shift macro lens, but real macro lenses can get up to 1:2 or 1:1 (object:image ratio) which is what you pay so much for. Lastly, the 20mm lens that I have for the GF-1 only has electronic aperture controls, so I believe the shallow depth of field is just due to the lens reverting to its native aperture (f/1.7) when unmounted.

Pretty neat eh?