What is an Extension Tube?

Our readers frequently ask us about extension tubes for macro photography. Since I am not much into macro myself, I have not explored this area of photography enough to qualify to write about it. While I have done some macro photography for product shots and ring shots in weddings with my Nikon 105mm f/2.8G VR lens (a very sharp lens that I absolutely love), I have not explored its full capabilities and I have not tried to use extension tubes and bellows to do crazy things that you can achieve with a true macro setup. Meanwhile, our readers have been gracious enough to fill in, and I have recently received the below post from one of our readers, Usama Nasir, who talks about what extension tubes are and how they are used in macro photography.

If you find yourself frustrated by the minimum focusing distance of your lens, if you constantly find that you’re unable to frame the shot you want, because you can’t get close enough to focus, then you may want to consider using extension tubes.

How Extension Tubes Work

An extension tube is an attachment that goes between your camera body and your lens. It’s not an optical element, so there is no glass involved. All it does, is get the lens further away from the focal plane. Now, the practical upshot of this, is that your minimum focusing distance gets smaller. So, with an extension tube, you can get closer to your subject and thus fill the frame with more of it.

For example, I have the Canon 24-105mm lens, which has a minimum focus distance of 1.48 feet (0.45 meters). The above shot is as close as I can get to this flower. Nice enough, but I like to get in closer, so I’m going to add one of the extension tubes (I have three of them and we’re going talk about their differences shortly). Extension tubes simply go on your camera body like a lens. So, I’m going to take my lens off, attach the shortest extension tube on the camera body, then attach my lens to the other end of the extension tube.

The reason I’m choosing the shortest one, is I don’t want to go in real far – I just want to get a little bit of boost in magnification. With this setup, I am now able to physically get closer to my subject and photograph at a greater magnification. Now, there is a trade-off to using extension tubes – they can eat up some of the light. I may have to increase my ISO or potentially decrease my f-stop (aperture) to get a little more light. And if I use a wider aperture, then I’m going to have less depth of field to work with. So, there is this trade-off of magnification versus depth of field. But what’s nice, is that I got in closer – something that I was not able to do before with the bare lens.

The nice thing is that I don’t have to worry about cropping my image in post-production just to try to get closer to my subject – I get to use more of the pixels in my camera. You can use extension tubes with any type of lenses: primes or zooms, portraits, or even macro! Extension tubes are an inexpensive way to get the kind of short focusing distances that you get from a dedicated and much more expensive macro lens.

Extension Tube Sizes

Extension tubes come in different sizes. I have a set of three Kenko Extension Tubes (here is the Nikon version). I have one that is 12mm; a longer 20mm one; and the longest one is 36mm. I can also stack these together. As I stack them, they obviously get longer. And, as they get longer, I get more extension, which means more magnification power. Once I attach this setup on my camera, I’m going to be able to get all the way into the full macro range, which is going to open up all of the macro concerns and practices that I’m going to have to think about as I’m shooting that close.

The effectiveness of extension tubes decreases as focal length increases. That’s because the additional magnification you get is the length of the extension tube over the focal length of the lens. Thus, while a 25mm extension tube will give you an additional 0.5x magnification on a 50mm lens, it will only give you 0.125x additional magnification on a 200mm lens. Thus, extension tubes are most useful on lenses less than 200mm. Here are the additional magnifications offered by three different sizes of extension tubes for 50mm and 100mm:

One other very important thing to understand about extension tubes is that some of them have electrical contacts that allow your camera to communicate with your lens, and some don’t (the above linked versions do).

If you get tubes that don’t, then you won’t have autofocus capability or aperture control. Now, Canon and Nikon both make sets of active extension tubes with full electronic contacts. While they work great, they are obviously very expensive. Kenko extension tubes that I personally use are much cheaper than brand versions and you could even get cheaper ones from other third party brands like Vello. My extension tubes have the much-needed electronic contacts, giving me full autofocus capability, and yet they cost much less than the Canon tubes.

Extension tubes are a very affordable way to start getting into macro photography. What’s more is that they are small, lightweight, and easy to carry around. If you are worried about whether you should invest in extension tubes, or go ahead and invest in a true macro lens, bear in mind that sometimes you’ll need to get a macro lens closer to your subject, so you’ll continue to use extension tubes, even if you eventually buy a macro lens. In the meantime, they’re a great way to start experimenting with close magnifications using your regular lenses in your arsenal.

Disadvantages of Extension Tubes

Extension tubes have some disadvantages compared to true macro lenses. One small disadvantage is that lenses that are not made to be true macro lenses may not be well-corrected for close-up usage. For example, a lens may work pretty well on its own but have noticeable fringing and softness in the extreme corners when paired with extension tubes. That’s not a huge problem and you can still do plenty of nice macro shots as long as you keep this in mind.

But there is one other, much larger disadvantage of extension tubes. Not only do they decrease your minimum focusing distance allowing you to get macro shots, but as a side effect, they also decrease your maximum focus distance as well! In other words, you will not longer be able to focus at infinity. In fact, you will barely be able to focus at any normal distance at all, so that macro will be the only thing you can do. Even portraits of people will not work with most lenses and tubes.

Finally, you also need to be careful when working with extreme wide-angle lenses. If I put the 68mm stack of tubes on a 20mm lens, I won’t be able to focus at all, because my minimum focusing distance will be pulled back into the inside of the lens.

Other Means to Get Closer

Extension tubes are not the only way to get closer to your subject. You can also purchase close-up filters, dedicated macro bellows that have much more flexibility than extension tubes and can potentially be used to move your plane of focus like tilt/shift lenses do (can get quite expensive) and you can also utilize adapters to use normal lenses in reverse position (which basically converts normal lenses into macro lenses). There are also other types of cheap DYI solutions that can effectively achieve the same results as using extension tubes or bellows. I would encourage Photography Life readers to dig into this subject more, because there is so much to explore in the world of macro photography.