What’s In My Camera Bag? Extension Tubes
The classic definition of macro photography is that the image projected onto the film plane or digital sensor should be the same size as the subject. At a 1:1 ratio, an SLR with a full-sized chip should have the ability to produce life-size magnification and focus on an area as small as 24×36 mm. Manufacturers sometimes describe a lens’s close-focusing capabilities as “macro” even if it doesn’t meet that definition and over time the term has gradually come to mean being able to focus on a subject close enough so the image is life-size or larger when viewing a 4×6 inch print. If you do the math, this requires a magnification ratio of approximately 1:4 and it’s within this more relaxed definition of macro that I tend to use on this post.
Conventional wisdom is that close-up photography requires expensive, specialized equipment and you can spend lots of money to make macro shots, you don’t have to break your piggy bank. Extension tubes provide additional separation between your lens and imaging chip that’s required for close-up photography. You might think of them as an alternative to the more complex and expensive extension bellows that some manufacturers offer as a close-up accessory. An inexpensive extension tube set, such as Pro-Optic that includes three tubes of different lengths (31mm, 21mm and 13mm) and can be used in various combinations to produce larger or smaller magnification based on total extension length. These tubes couple with your camera metering mechanism and usually offer full AF compatibility. Tip: Extension tubes will reduce the amount of light falling on the sensor but your camera’s metering system should automatically compensate for any light loss.
Caption: I photographed this flower in my North facing kitchen window using a Canon EOS 50D and an EF 50mm f/1.8 lens at ISO 200. A sheet of white paper was held on camera right during the exposure to provide fill. Exposure at ISO 200 in Aperture priority mode was 1/4 sec at f/16 to maximize depth-of-field. © 2011 Joe Farace
Caption: This image was made with the identical set up as the previous one but a 13mm extension tube was attached to the lens and mounted on the camera. The extension tube produced an exposure of 0.8 sec at f/22 and ISO 200. © 2011 Joe Farace