An extension tube is a hollow tube that fits between your lens and the body of your camera. An extension tube is used to alter the MFD (minimum focus distance) of the attached lens. They allow you to focus on subjects that are closer to the camera and achieve greater magnification.

Images in this post use a 50mm lens with a 12mm extension tube.

Gabby up close by Paul Sager, on Flickr


The Canon FD 50mm f/1.2L lens used in these images dates from 1980. The lens is manual focus, from back when everything was manual focus in 1980. The FD 50L had a reputation (then) for being the “most advanced 50mm lens” of its time, mainly due to the aspherical design that kept the size and weight WAY down for the f/1.2 aperture size.

The lens has a MFD of 0.5 meter or about 20 inches. Twenty inches already is a relatively short / close minimum focus distance. Adding a 12mm extension tube adjusts the lens such that it won't focus at all until you're about 10 inches or closer from the subject.

Gabby up close


Shot wide open at the minimum 20 inches, the f/1.2 aperture is razor thin. Adding the extension tube further changes the lens properties as the f-number 'aperture' is a ratio of the focal length to effective aperture diameter. Moving the 50mm lens another 12mm from the sensor via the extension tube makes the depth of field even 'thinner' for the same aperture setting on the lens. At f/5.6, the sharp depth of field is just wide enough to cover Gabby's eye in profile, below.

Gabby up close


Canon was one of the pioneers of "super-speed" lenses. In the 1960s and 70s, quality films were still fairly slow speed, so super fast lenses served a very tangible purpose. To shoot a 100, 64, or even 25 ISO film in anything but the brightest light requires lenses that dip below f/2. Canon made several of these ultra fast lenses for the FD system, include the initial L-series releases in 1979-81 of the FD 24mm f/1.4L, FD 50mm f/1.2L, and FD 85mm f/1.2L lenses.

Gabby up close


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