Thursday, June 30, 2011

Up Close and Personal, Part 2

When you focus a lens, the barrel is geared to move the elements closer and further away from the sensor -- the further the glass is from the sensor, the closer the lens will focus -- but lenses have a finite amount of travel built into them, so there's a limit to how close you can go. By adding extra space between the lens and camera body, you can effectively focus closer while increasing the magnification of your subject . . . this is the essence of macro-photography.

Since true macro lenses are often pricey and offer limited versatility, extension tubes are the best alternative to begin experimenting with close-up photography. These hollow cylindrical spacers operate under the same principle as any lens normally would: they increase the distance of the glass from the sensor, allowing closer focus and more magnification. The only disadvantage of using extension tubes is that you lose the ability to focus at infinity -- by enabling the lens to focus more closely, you take away its ability to focus far away.

Extension tubes are available in varying lengths (e.g.; 12, 20, 36mm) and can be used individually or stacked together. Remember: the greater the extension, the greater the magnification and if the extension is equal to the lens focal length, you will see life-size magnification. If you only have a short extension tube, this formula tells you you'll get more magnification when using shorter focal length lenses. That's why it makes sense to invest in a set of longer extension tubes to use with your longer lenses because you'll have a narrower field of view and larger working distance between the lens and your subject.

Longer extension with a longer lens is the perfect combination for macro-photography of wildlife in nature. I like to work with my 18 - 105mm lens set at 105mm and a 36mm extension tube for extreme close-ups and a 12mm tube for a less dramatic effect. All of these images were created using those 2 lens/tube configurations, with the first (trout), third (golden stoneflies), and last (largemouth bass) photos taken with a 36mm tube, and photos two (golden stoneflies) and four (salmonfly) with a 12mm extension tube.

Under ideal conditions (i.e.; bright sunlight, no wind!), I attempt to shoot at a minimum aperture of F16 -- at ISO 200, this normally means a shutter speed of 1/60th of a second. Don't forget you lose 2 full stops of light when using extension tubes and the depth of field is incredibly minute to begin with, so a small lens opening is mandatory. Yes . . . slow shutter speeds, extremely shallow DOF, with breathing and moving subjects . . . that's the beauty and the challenge of photographing nature Up Close and Personal!