Let’s say that 45 days ago you asked me the question, “What’s an extension tube, and what’s it used for?” I would have been forced to reply, “I have absolutely no idea.” Truth; but no longer. Let’s just say I know the answers to those questions — and I’m now an enthusiastic convert to something I wish I’d known about years ago.
In short, an extension tube is a non-optical (i.e., there’s no glass inside) lens accessory with a male lens mount on one end, and a female lens mount on the other, and blank space of some depth in between. It’s purpose is to move a lens farther away from the film or sensor plane, with the net effect of enabling hyper close-up focusing with a lens otherwise not designed for macro-type work — with a slight sacrifice in light intensity. You end-up with things like this:
Extension tubes are well-known by many photographers, but for me, I’d never heard of them, and consequently didn’t have any clue what I was missing out on.
Macro photography has great appeal to me. While my own style is still developing (bad pun), I tend to like taking photographs that have a lot of visual interest, and where there’s an interplay of shapes, light and shadow, and often with interesting cropping, and unexpected angles or fields of view — shots that reveal things in a new light, or that puzzle the eye. A lot of macro photography can easily fall into that category.
After hearing about extension tubes, I happened upon an episode of the Film Photography Podcast where the awesome Leslie Lazenby was talking about them. By then, I’d already known their purpose, but Leslie’s dialog about it made we want to get one for my Pentax 645.
Pentax made a traditional three-piece graduated set of extension tubes — a common format for them — as well as a “helicoid” extension tube that’s adjustable over a set range. As near as I’ve been able to find, the traditional three-piece may not have been available in North America, but the helicoid version is readily available today on the secondhand market. When I checked KEH recently, they had one in “excellent” condition for a fair price, so I ordered it up.
The tube is a simple affair, and it fits the description I gave earlier. There is no electrical coupling of any kind between the lens and the camera body, and no special mechanical coupling either. The net result is that aperture stop-downs are visible through the viewfinder without enabling the depth-of-field preview lever, and for users of auto-focus 645 models, you’ll have to manually focus. But wow, is it effective!
I tried the tube with several of my lenses, and the results were pretty impressive. Even with the prime 75mm lens, I was able to focus shockingly close to things, and the 45-85mm zoom provided even more flexibility; I could fill the frame with a field of view about the same size as a large postage stamp.
It’s worth noting that the helicoid adjustment range is pretty pitiful — enough that I’m not sure why Pentax even bothered. The net difference in the field of view is quite small at the end of the day.
Getting an image in focus can also be a challenge. My approach is to try and get the focus relatively close to right, but then move the camera closer to or farther away from the subject to get the focus effect I’m going after. Because of the always-on aperture preview, it’s a natural tendency to want to open the lens up all the way so the image on the focusing screen is bright, but then of course you’re going to end-up with an exceptionally narrow depth-of-field. That could be the effect you want. If not, stop down — but you will need a considerable amount of light to be able to ensure any level of focusing accuracy, and you won’t be able to stop down much and still have a usable preview of the shot.
That tradeoff doesn’t seem too big in my book, as I’ve already liked what I see through the viewfinder — and on film. Like this:
Is an extension tube a replacement for a proper and true macro focus lens? I would have to say no. But it is a comparatively inexpensive alternative for playing with macro photography using the lenses you already own, and it opens-up a whole new arena of creative photography. As a result, it strikes me as a must-have accessory for any serious (or experimental) photographer.