If you want to get up close to your subject, closer than you can by setting your lens to its minimum focusing distance, then extension tubes are an excellent way of doing so.
When you turn the focusing ring of your lens away from infinity, the front element moves out from the lens body. The distance between the front element and the sensor (or film) plane is called extension. When your lens is set to its minimum focusing distance, the front element can move no further forward. You have reached the limit of the lens’s design.
An extension tube is a hollow tube that fits between your lens and camera body. It moves the lens further away, increasing the extension of the front element. In turn, this lets you move the lens closer to the subject, increasing magnification, and in some cases even matching the 1:1 magnification of a true macro lens.
This is the Fujifilm MC-EX 16 extension tube that I use. The electrical contacts, that allow the lens and camera body to communicate, are visible at the back (more on the importance of this later).
This is the Fujinon 35mm f/1.4 lens mounted to an X-Pro 1 camera. The distance between the front lens element and the sensor plane is the extension. This figure helps determine the closest point the lens can focus on (in this case 28cm), and subsequently the magnification.
Below is the same lens with the MC-EX 16 extension tube added. You can see that the front element of the lens is now 16mm further away from the sensor plane. Now the lens can focus on a much closer point.
Extension tubes versus macro lenses
Extension tubes are a great tool, but for the best possible optical quality and the most versatility you should choose a macro lens if you can. The reason for this is that increasing the extension of a non-macro lens means that you are using it outside the limits it is designed to work within. Macro lenses, on the other hand, are designed to give their peak optical performance at close focusing distances. They can also focus at infinity – whereas a lens fitted with an extension tube cannot.
The main benefit of extension tubes is that they are small and light. You can carry them around in case you need them, and leave your macro lens (if you have one) at home. They are ideal for anybody who travels a lot, or who wants to keep the weight of their camera bag down.
Cheap extension tubes versus good quality ones
You can buy inexpensive extension tubes from Amazon or eBay. These may look like a great deal but they break the electrical connection between your camera and the lens. If your lens has an electronically controlled aperture that means, you can’t stop the lens down. The camera also can’t record the aperture setting in the EXIF data.
Your camera will still work, and meter the subject to give you the correct exposure. But, given that depth of field at the widest aperture is incredibly narrow, and that you need to stop down to improve image quality, these cheap extension tubes are not of much practical use. They are only useful if you have a lens with a manual aperture ring.
The best ones to buy are those made by your camera manufacturer, or by a third party like Kenko or Vivitar, who make extension tubes that maintain the electronic connection between lens and camera. There is usually a choice of two sizes. The widest will get you closer, and the narrowest will come in useful when you don’t need to be quite so close. You may want to start off buying one or the other, but will probably end up buying both to cope with different situations.
Extension tubes and magnification
Extension tubes are most effective when used with lenses of focal lengths between 24-100mm. They are not so effective when used with telephoto lenses (for these, use a close-up lens). You can’t use an extension tube with some wide-angle lenses as it becomes impossible to focus with it fitted.
To see how much magnification an extension tube will give you with a specific lens, check the specifications on B&H Photo Video (United States) or Wex Photographic (UK). You may also be able to find the information on the manufacturer’s website. The instruction sheet that comes with the extension tubes also has this information, and you may be able to find a copy online.
There’s an easy formula for calculating how much extra magnification an extension tube will give you:
Increase in magnification = extension distance/lens focal length
For example, my Fujinon 35mm f1.4 lens has a magnification of 0.17x at its closest focusing distance of 28cm (I found this information in the spec sheet). Adding a 16mm extension tube means the increase in magnification is 0.45 (16/35), giving a total of 0.62x (0.45 + 0.17). This figure is a little academic, but it’s useful for evaluating whether you can add an extension tube to your lens and reach the 1:1 (1x) magnification, offered by most macro lenses.
Extension tubes in action
These photos show you how much difference an extension tube can make.
Do you own an extension tube? Which ones do you have and how useful are they? Let us know in the comments, it will be useful for other readers who are thinking about buying some.
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