Adding an extension tube

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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7 Responses to “Adding an extension tube”

  1. Mike Powell Says:

    Theory is great, but more importantly your images show that the theory works in practice. Wonderful shots of that beautiful female Eastern Ringtail.

  2. Larry de March Says:

    Working distance and closest focusing distance are different. The closest focusing distance (which manufacturers report in their lens specifications) is the distance between the plane of the sensor (or film) and the subject; working distance is between the front of the lens and the subject.

    • waltersanford Says:

      Thanks for the clarification, Larry. I wrote the blog and added the parenthetic statement afterward. I actually hesitated ‘cuz I wasn’t sure whether “closest focusing distance” is the same thing that Fujifilm calls “shortest shooting distance.” In retrospect, it seems obvious the two are one in the same. I’m going to edit the post, but leave this comment thread. Thanks again!

  3. Larry de March Says:

    Minimum working distance and reproduction ratio are what’s important.

  4. Swift Setwing dragonflies (males) | walter sanford's photoblog Says:

    […] camera was set for an aperture of f/11. I forgot to decrease the aperture to f/16 (one of the lessons learned from recent field testing), although depth of field wasn’t an issue from this viewpoint of […]

  5. Banded Pennant dragonflies (males) | walter sanford's photoblog Says:

    […] camera was set for an aperture of f/11. I forgot to decrease the aperture to f/16 (one of the lessons learned from recent field testing). Although depth of field (DoF) wasn’t an issue for the lateral view […]

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