Feb 18, 2009

Macrophotography: Extension Tubes

Image from Kenko

Using extension tubes is one of the cheaper alternatives in doing macrophotography. These tubes are exactly just that, tubes that extend or move the lens away from the camera film or digital sensor. As a result, the lens can focus closer, magnifying the subject in the process. The longer the extension, the greater the magnification.

You will be encountering 3 limitations though. First, extension tubes cause light loss. The farther the lens from the camera film or digital sensor is, the greater the light loss. As a result, this will cause a darker viewfinder and longer exposures.

Second, the longer the lens' focal length, the lower will be the magnification. Conversely, the shorter the focal length, the higher the magnification. This can be computed using the formula below

M = Y/X


M = magnification
Y = total length of the extension tubes in mm
B = lens' focal length in mm

As a result, if you have a 50mm lens and the total length of the extension tubes is 68mm, magnification will be 1.36x or 1.36:1. On the other hand, if you have a 100mm lens attached to a 68mm extension tube, the magnification will just be less than life-size or 0.68x to be exact.

Third, the shorter the focal length of the lens, the closer the subject needs to be to the lens to achieve focus. All lenses has a minimum focusing distance. For example, the minimum focusing distance of the Canon 50mm lens is 0.45m or 1.5 ft. Attaching a 68mm extension tube to this lens results to a reduction in the minimum focusing distance to about 4 inches. If you are dealing with a lens whose focal length is shorter than 5omm, there will be a high probability that the minimum focusing distance between the subject and the lens will be very small. This will be quite impractical if your potential subject is an insect.

By the way, you may be wondering what is the process for computing the minimum focusing distance for a lens attached to an extension tube. It is not quite exact, well as per my research, but I found a great forum thread which discussed this topic.

There are many types of extension tubes depending on the manufacturer. One of the most popular, which I currently use, is manufactured by Kenko (see image above). It is composed of 3 tubes with various lengths, 12, 20 and 36mm respectively. You can use the tubes separately or you can combine or stack all three to get the 68mm length.

Images from Amazon

Canon has its own set of extension tubes, albeit more expensive than the Kenko tubes. One is 12mm in length while the other one is 25mm. You can also use these tubes separately or you can combine both to get 37mm.

If you like to experiment or the Do-It-Yourself (DIY) type, you can also make your extension tube. As I mentioned above, the concept behind these tubes is just to move the lens away from the camera film or digital sensor. If this is the case, you can use any material for the tube as long as it is sturdy and you can place the right adapters so that you can attach it to the lens and camera body. I found two DIY extension tube examples from the Net, one made from a PVC pipe and the other one from a Pringles can, both did a great job in getting great macro images.

You may be asking now, what is the difference then between the DIY and the commercial tubes (except of course for the price). Well, from my standpoint, that will just be the presence or the lack thereof of electronic contacts connecting the lens and camera body. The commercial tubes have electronic contacts which allow you to get camera metering and even focusing. For the DIY tubes, these do not have the contacts thus you need to manually set the metering and even the aperture of the lens. I will be discussing how to do this in my next post when I tackle how to use reversed lens where you will encounter the same problem, the lack of electronic contacts between the lens and the camera.

To give you a sample of what you can get using extension tubes, you can find below a slideshow of the images I captured using a Canon 50mm lens and Kenko extension tubes.

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