Extension Tubes for Macro Photography: The Affordable Alternative That Works

Very few accessories can contribute so much to our gear for so little money.

What are extension tubes in photography and what are they used for?

Extension tubes are hollow accessories that are placed between the camera body and the lens to alter the minimum focusing distance. They do not include any kind of optical element, and all they do is move the lens away from the focal plane. The practical result is that we can get closer to what we want to photograph, project a larger image onto the sensor and thus achieve a more detailed photograph. They are mainly used in close-up and macro photography, but they also have a place in product photography, portraiture and in any other situation where we do not have to move too far away from the person or subject of interest.

Extension tubes are sold in the form of combinable sets of, generally, two or three pieces of different lengths. They can be used with any type of lens, fixed or zoom, although they probably will not work with wide angles. For example, if we place a set of 68 mm tubes on a 20 mm lens we will no longer be able to focus because the minimum focusing distance will have moved inside the lens.

Likewise, the effectiveness of extension tubes decreases as focal length increases. In other words, you’ll see more change using them with a 50mm lens than with a 300mm lens.

Electronic contacts

This is a very important aspect. Some models have electronic contacts that allow the camera to communicate with the lens and others do not. Well-known brands such as Canon, Nikon or Olympus make or have made extension tube sets with complete electronic contacts. They certainly work very well, although they also cost a good amount of money.

Since extension tubes are only spacers and do not contain optical elements, it is much easier for third-party manufacturers to put competitive products on sale. In that sense, Kenko offers very valid alternatives, and in a low price range we have Meike or Neewer, among others, which offer reasonable quality, so buying extension tubes without connections, and therefore without the possibility of autofocus or aperture control, seems to us to be an excellent way to throw money away.

How do extension tubes affect image quality?

Unlike close-up lenses (see comparison with tubes by following the link), extension tubes do not include any optical elements. This means that in most cases they will have very little effect on image quality. The tricky part here is that each lens reacts very differently to the use of tubes, so it is difficult to give a general answer to this question.

When manufacturers design the optics of a lens, they take into account distortion, which they try to correct as much as possible, especially at the most important points of its focal range. When focusing, the lenses move within the lens and usually the distortion varies depending on the distance at which the focused subject is. The result is that some lenses are sharper than others when used at the minimum focusing distance.

Take a macro lens, for example. Designers know that we will be using it mostly at its minimum focusing distance, and they correct the distortions so that the lens offers maximum sharpness at that point. Telephoto lenses, on the other hand, are typically used to focus on objects that are at a certain distance, and distortions have been corrected with that in mind.

What all this means is that every lens works differently, that not all lenses perform well outside their designed parameters, and that an expensive, reputable lens cannot be taken for granted to be super-sharp at its minimum focusing distance. And also that extension tubes will magnify those imperfections on the sensor.

Vignetting

Another side effect of extension tubes is that they can cause vignetting when using lenses at their maximum aperture or close to it. The amount of vignetting depends on the individual lens, but also on the length of the tubes. A 12mm tube is not a big problem, but when we talk about 20mm you have to be careful not to open it all the way if you want to counteract this effect.

Focusing to infinity

When using extension tubes, it is no longer possible to focus to infinity. In practice, this is almost never a problem because most people use them to focus on something very close, and it can even be an advantage when we want to blur the background and do not need a large depth of field..

Extension tubes and f-number

One thing we’ll notice if we’re working in manual is that there’s a significant overall loss of light when using extension tubes. This happens across the entire image equally, so we’re talking about something different from the vignetting we mentioned above. By moving the lens away from the sensor, the f-number is actually increased, so the image darkens and the depth of field increases as if we’d changed the aperture with the camera dial. The difference is that the camera doesn’t know that the lens has moved away and there’s been a change in aperture.

In practice, this is a relative problem because macro photography is a discipline that is usually done in very good light conditions or with flash. Also, we won’t notice anything if we’re working in automatic or semi-automatic mode, because the camera itself will take care of compensating. But if we’re shooting in manual, what we need to remember, as a general rule, is that as we get closer to 1:1 magnifications, the effective f-number of the lens will have changed by about 2 stops, meaning we’ll need to compensate with a higher ISO or a shutter speed 4 times longer than we would need without the tubes.

Effects on autofocus

Another consequence of altering the f-number in this way is that less light reaches the camera’s autofocus sensor if you’re using a DSLR (digital SLR). As a result, you may find that autofocus performance drops in low light if you’re working with extension tubes. This is less of an issue with mirrorless cameras where autofocus is performed on the image sensor using phase detection autofocus, but it can still have a small impact on performance.

In practice, whether you’re using a DSLR or a mirrorless camera, photographers often use extension tubes with static subjects in order to be able to focus manually, so this drawback is, with a few exceptions, a minor issue. It should also be remembered that this loss of light will occur with any brand of extension tube. It’s simply a matter of physics.

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