Optics theory
The net effect of adding an extension tube between a lens and camera body is the “working distance” is decreased, that is, the distance from the front of the lens barrel to the subject is decreased. A smaller working distance means the same lens will focus closer to the subject, thereby increasing magnification.
The effect is greater at shorter focal lengths, as shown by the following table of magnification for the two extension tubes sold by Fujifilm USA.
Table courtesy Fujifilm USA.
Theory into practice
An Eastern Ringtail dragonfly (Erpetogomphus designatus) was spotted along the Potomac River at Riverbend Park, Fairfax County, Virginia USA. This individual is a female, as indicated by her terminal appendages and rounded hind wings.
Both photos in this set were taken using my Fujifilm X-T1 digital camera, Fujinon XF55-200mm zoom lens plus a “Fotasy” brand 16mm extension tube, and Fujifilm EF-X500 shoe mount flash. The lens was set for a focal length of 200mm (~350mm, 35mm equivalent).
At 200mm, the working distance of the lens is 905 mm (90.5 cm, ~35.63 in), or approximately three (3) feet. With a 16mm extension tube mounted between the lens and camera body, the working distance is reduced to 595 mm (59.5 cm, ~23.43 in), or approximately two (2) feet. At a focal length of 55mm, adding the extension tube would result in photos that look more like “macro” photos; at 200mm, adding the extension tube resulted in photos that look like a lens with a longer focal length was used to take the shots.
The first photo is uncropped. I’ve never been able to get a shot like this using a mid-range telephoto zoom lens such as the Fujinon 55-200mm. The 16mm extension tube is the difference-maker.
The last photo is cropped slightly, but not enough to affect the apparent magnification. I look closely at the edges of my photos. In this case, I cropped the photo to remove some distracting elements and leading lines.
Editor’s Notes
I bought a set of two “Fotasy” brand extension tubes (10mm, 16mm) years before Fujifilm released their set of two. The advantage of the Fotasy extension tubes is a set of two costs a little more than half as much as a single Fujifilm extension tube. The disadvantage is compatibility. The Fotasy extension tubes work with my Fujinon XF18-55mm (27-82.5mm, 35mm equivalent) “kit” lens and Fujinon XF55-200mm mid-range telephoto zoom lens; they don’t work with my Fujinon XF100-400mm (152-609mm, 35mm equivalent) telephoto zoom lens. For what it’s worth, the 100-400mm lens was released after the Fotasy extension tubes. Bottom line: I recommend Fujifilm extension tubes, despite the fact that they are significantly more expensive than Fotasy extension tubes.
The Depth of Field is razor thin, in contrast with shooting without an extension tube. I shot the preceding photos at f/11; f/16 or smaller would have been better.
In order to reduce “camera shake,” I almost always shoot in shutter priority mode using the reciprocal rule. Remember, it’s the 35mm equivalent that matters: since my lens is ~350mm, the shutter speed should be set for at least 1/350s; in this case, it was set for 1/1,000s. A monopod was used for added stability.
Copyright © 2017 Walter Sanford. All rights reserved.
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