Extension Tubes and Telephoto Lenses
by Bob Cammarata
Extension tubes have become a staple in just about every macro photographer’s equipment bag. Typically sold in sets of three (usually in 12mm, 20mm and 36 mm sizes), they are fitted between the camera body and the lens either singly or stacked together. We commonly associate their use with permitting our macro lenses to focus even closer for greater than life-size reproductions but these versatile and in-expensive tools are not limited only to macro work. The primary function of the hollow ’tubes is to extend the rear element of any lens away from the film plane or sensor, thus allowing the lens to focus closer. The end result is a bigger image in the frame. But the ability to focus closer does not come without compromise. Up to two stops of light are lost, depth of field is reduced exponentially and the lens loses its ability to focus to infinity.
Extension Tubes with Telephoto Lenses
The practice of adding extension tubes to super telephoto lenses is no big secret. Serious wildlife photographers have been using this technique for decades to squeeze out a few more feet of close-focusing capability…particularly when stalking non-skittish wildlife subjects or applying acquired stealth techniques which permit close access.
This White-breasted Nuthatch was perched around 13’ away from a photo blind…where a 600 mm lens with a stack of extension tubes was poised and waiting. By itself, that particular telephoto lens focuses from around 21 feet to infinity. Without extending the lens, critical focus on the bird would have been impossible without moving the blind back eight feet. By setting up closer to the subject, the end result is a much larger image.
For those active bugs and insects which never seem willing to sit still and cooperate, adding extension tubes to a 300 mm lens is a practical solution to the challenge of attempting to achieve full-frame crops from well outside the critter's “circle of safety” (…which in the case of this Blue Dasher, was around eight feet). When trying to get closer with more traditional close-focusing lenses becomes a crusade in futility, a longer lens and a few extension tubes can yield the same results with fewer missed opportunities.
And even larger reproductions from the same working distance can be achieved by adding a 1.4x teleconverter between the lens and the stacked extension tubes. An additional stop of light is lost but on a bright sunny day, it’s still possible to achieve a shutter speed fast enough to freeze the action of the most energetic bugs, like this Needham’s Skimmer, while maintaining acceptable depth of field.
Needham's Skimmer (female)
Quite often, the aforementioned “Circle of Safety” will apply to the photographer as well as the subject….those times when a full-frame image is desired but one really NEEDS to back up!
Adding extension tubes to standard telephoto lenses can fill that void and create another level of versatility to a wildlife photographer’s arsenal..
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