Photo of two extension tubes (round, black cylinders) for Canon SLR cameras
Extension Tubes for Canon FD Mount Cameras

As photographers it seems we’ve always got our eye on a new piece of gear to expand the capabilities of our kits, but camera equipment is notoriously expensive and finances often get in the way of those purchases. There are, however, a certain type of inexpensive lens adapters that can add a whole new dimension to your photography without breaking the bank. They’re called extension tubes, and if you don’t already have some you’re going to want to read on!

What Are Extension Tubes?

Extension tubes are essentially just cylindrical spacers that can be mounted between an SLR/DSLR camera body and its lenses. This increases the distance between the rear of the lens and the camera’s imaging plane (film / sensor), allowing the attached lens to focus on closer objects than it was designed to while also greatly decreasing its field of view. The result is a dramatic (perceived) increase in magnification — or in other words, an inexpensive way to shoot macro photography with the lenses you already own!

Typically, new extension tubes are sold in sets of three (short, medium, long) with their lengths labeled on the side in millimeters. You can also purchase used extension tubes à la carte on sites like eBay. When shopping, keep in mind that the longer the extension tube is, the more the subject of your photographs will be magnified. I recommend purchasing at least a short and medium option, which can actually be stacked together if additional magnification is needed.

What Lenses Will Work?

Some types of lenses and focal lengths work better with extension tubes than others. You may want to do some experimentation on your own to find a combination that works best for you, but in general you will have the best luck with short or medium prime lenses. A 35mm or 50mm lens, if you have one, is a great place to start. Close-focus and telephoto lenses do not work well, and expensive lenses will generally perform better than inexpensive lenses as they (usually) contain better optics.

A Canon F1 SLR camera with a 50mm extension tube and 50mm lens attached
A Canon New F-1 with a 50mm Prime Lens and 50mm Extension Tube Attached

How To Use Extension Tubes

Attaching an extension tube to your camera is simple:

  1. Remove the lens or lens port cap from your camera body.
  2. Attach your extension tube(s) to your camera body (in the same way you would mount a lens) to get your desired amount of magnification.
  3. (Re)attach your lens to the end of the extension tube.

There should be markings on your extension tubes to help you properly align them to your camera body, as well as markings for attaching your lens to the end of the tube. You may also notice electronic contacts or mechanical levers on the ends of the extension tube. These allow the camera to continue controlling your lens’ iris while the extension tube is attached.

Focusing

Now that you have your extension tube(s) mounted, you will likely notice some difficulty in focusing on a subject. This is one of the first major drawbacks to using extension tubes over a dedicated macro lens. The extension tubes change the lens’ flange focal distance by such an extreme amount that it can no longer focus to infinity. In fact, you might find the focus ring on the lens is no longer useful at all!

The easiest way to focus with an extension tube attached is by moving the entire camera toward / away from your subject. This can either be achieved by physically holding the camera and leaning back and forth with it, or on a tripod through the use of a special focusing rail / slider. If you do decide to shoot handheld, I recommend a shutter speed no slower than 1/125 as the extra magnification tends to cause much more motion blur than you would normally expect.

Another focusing difficulty, particularly when shooting handheld, is caused by extremely shallow depth of field. Since your film or digital camera will likely preview the image you are shooting with a wide open aperture, you may be surprised to find you have very little usable depth of field. To make focusing easier, I prefer to use extension tubes with a minimum ISO of 800. This allows me to stop my lens down to at least f/8 or f/11 (under somewhat normal lighting conditions) and gain much deeper depth of field.

Metering

Metering can also become tricky with the addition of extension tubes. I strongly recommend using a camera with a through-the-lens (TTL) metering system and taking readings off of a gray card to determine proper exposure. In doing this, you will probably notice your subject requires much more light than it would need without an extension tube. This is because the further an extension tube moves a lens from the imaging plane, the weaker the light reaching it becomes. For this reason, you will achieve your best results in full sunlight or by using artificial lighting specifically designed for macro photography.

The use of a handheld light meter with extension tubes is possible, however the process is somewhat complex. In a nutshell, the light loss introduced by each extension tube needs to first be calculated using the inverse square law formula and then each meter reading must be adjusted accordingly. Perhaps I will write a future article to explain this process in greater detail.

Extension Tube Drawbacks

As mentioned above, the use of extension tubes introduces a few complications related to focusing and metering, as well as reducing the amount of light reaching the imaging plane. In addition, extension tubes will also occasionally introduce some of the following issues:

  • Light leaks – Most often caused by poorly constructed extension tubes and/or the improper seating of the lens / extension tube.
  • Optical Abberations – More specifically chromatic aberrations or “fringing.” This is caused by the extreme magnification of lower-quality optics which tends to exaggerate their flaws.
  • Vignetting – Typically occurs when multiple extension tubes are stacked together or the lens aperture is wide open.

Conclusion

Extension tubes are a fantastic, affordable way to expand your capabilities as a photographer, however they do have several drawbacks compared to dedicated macro lenses. Understanding their limitations and working within those parameters is the key to producing incredible imagery with extension tubes!

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