What is a Camera Extension Tube?

What is a Camera Extension Tube?

If you’re just starting out with macro photography, you can get a dedicated macro lens for your camera. Or you can pair a macro extension tube with a lens to produce exceptional results! To get even closer to your subject, pair extension tubes with macro lenses for greater-than-macro magnification.

What is an Extension Tube?

An extension tube is a hollow tube that fits between your lens and the body of your camera. They allow you to focus on subjects that are closer to the camera and achieve greater magnification. As a result, they’re also sometimes called macro tubes because they can allow you to create macro images without a dedicated macro lens.

Because extension tubes don’t contain any actual optics, they can be very inexpensive. They don’t introduce new distortions the way some add-ons (such as filters and teleconverters) can. They are also very flexible, allowing you to stack multiple extension tubes and can be used with any lens you own.

How Extension Tubes Work

stack of extension tubes
Lenses focus light a specific distance to the sensor behind it. Every lens has a minimum focus distance where it’s able to project the focused image onto the sensor. If an object is too close to the lens, that distance falls behind the sensor.

By moving the lens away from the body, an extension tube adjusts the focal point. This allows you to focus on objects closer to the lens than you could otherwise.

One trade off, though, is that it also moves your farthest focus distance closer to the lens as well. When using an extension tube, you’re going to lose the ability to focus at infinity. With some lens and extension tube combinations, you may only be able to focus a few feet away. Extension tubes should only be used when you want to focus as close as possible to achieve the most magnification.

close up of a kiwi

How much additional magnification you can get depends on the combination of lens and extension tube you choose. You can determine how much additional magnification you want by dividing the extension tube length by the original focal length.

For example, the incredibly popular Canon EF 50mm f/1.8 STM has a native maximum magnification of .21x. Using a 25mm extension tube, you can add .5x magnification, bringing the total magnification to .71x. Using both a 12mm and a 25mm extension tube will add .74x magnification, bringing the total to .95x, very close to a true macro lens.

This also means that an extension tube has a larger effect on shorter lenses. A 25mm extension tube will add .5x magnification to a 50mm lens. But it will only add .25x magnification to a 100mm lens and .125x to a 200mm lens.

How to Use an Extension Tube

Three extension tubes 36mm 20mm and 12mm

Using an extension tube is as simple as connecting the extension tube in between the camera body and lens. Once the extension tube and lens are in place, there are no additional controls or mechanics you need to worry about.

The more you magnify the image, the more likely camera shake may affect your image. Just as with using a longer focal length, you need to use a faster shutter speed, secure your camera to a tripod, or use a flash to freeze any motion and ensure a sharp shot.

Extension tubes will change the effective aperture of your lens. Your f-stop is the measurement of the focal length divided by the diameter of the pupil of the aperture. For example, if you’re using a 100mm lens whose aperture is 25mm in diameter, the f-stop is f/4.0 (100mm/25mm). If an extension tube combination gives you an effective focal length of 150mm, the same aperture setting (25mm diameter) will give you an effective f-stop of f/6.0. Less light will be hitting the sensor, so you’ll need to compensate for that.

You also need to make the same adjustments when shooting with an extension tube as when using a macro lens. Most importantly, when you focus on an object that’s so close to your lens, your area of focus is going to be incredibly small. At these focusing distances, the depth of focus will be measured in millimeters. You will need to use smaller apertures, focus extremely carefully (manual focus will likely be more reliable than autofocus here), and potentially use tricks such as focus stacking to get exactly what you want in focus.

photo of small frog

Pros and Cons to Using an Extension Tube

An advantage to using extension tubes is that they can be very inexpensive. You get macro capabilities for far less than a dedicated lens. Also, because they don’t contain any actual optics, they don’t introduce new distortions the way some add-ons (such as filters and teleconverters) can. They are very flexible, allowing you to stack multiple extension tubes, and can be used with any lens you own.

Extension tubes themselves are very light and compact. When packing your camera bag, if you can use extension tubes with another lens, you will save space and weight versus adding an extra dedicated macro lens.

While extension tubes don’t introduce distortions, they can magnify existing problems. Some lenses are not very sharp at their closest focus distances. If you use an extension tube to one of those lenses, you can magnify those problems.

A downside to extension tubes is, aside from moving your minimum focusing distance, they also move your farthest focus distance. When using an extension tube, you’re going to lose the ability to focus at infinity. With some lens and extension tube combinations, you may not be able to focus more than a few feet away. Extension tubes should only be used when you want to focus as close as possible to achieve the most magnification.

Finally, adding an extension tube changes both your effective focal length and aperture. By essentially making your lens a little bit longer, you make it more prone to camera shake. Your f-stop, which is your focal length divided by the diameter of the aperture’s pupil, also becomes smaller, so less light will end up hitting your sensor.

For example, if you’re using a 100mm lens whose aperture is 25mm in diameter, the f-stop is f/4.0 (100mm/25mm). If an extension tube combination gives you an effective focal length of 150mm, the same aperture setting (25mm diameter) will give you an effective f-stop of f/6.0. You will need to make sure you compensate for both of these effects.

Types of Extension Tubes

Because of how simple extension tubes are, you can find incredibly inexpensive ones. But not all extension tubes are equal and you should consider a few things when choosing them.

Extension tubes may or may not be compatible with your camera. If they aren’t, you will lose the ability to electronically adjust the aperture and use autofocus. Because almost no modern lenses have manual aperture controls, non-electronic extension tubes will leave your lenses wide open, which may be extremely difficult to use, due to the tiny depth of focus you’ll have.

Both Canon and Nikon make extension tubes in a couple of different sizes:

Model Length
Canon EF 12 II 12mm
EF 25 II 25mm
Nikon PK-12 14mm
PK-13 27.5mm

Other major lens manufacturers aren’t currently making extension tubes, but there are a number of other third parties such as Kenko, Vello, and Neewer.

When choosing an extension tube, consider electronic aperture control and autofocus. Because there’s no optical performance difference between extension tubes (due to there being no glass elements to interfere with light transmission), lower budget extension tubes might be best for your needs.

One factor in choosing a more expensive extension tube is if you need more robust build quality. Cheaper extension tubes need to be treated more carefully to avoid damaging them. In particular, some cheap extension tubes have reputations for having weak threads that can cause them to get stuck to your lenses. If you’re unable to remove the extension tube, that lens will not be usable for anything other than macro photography.

Choosing an Extension Tube

Extension tubes can be used with almost any camera mount. Keep in mind not to use an extension tube if you’re using a lens with a different mount from your camera body. You might not have any problem using extension tubes and an adaptor at the same time, but it does increase potential points of failure.

Because you will likely be using an extension tube with a smaller aperture, you may want to pair it with a camera that have better low light performance. If your camera struggles at higher ISOs, you might struggle to properly expose your images.

Because the entire point of using an extension tube is to increase magnification, you can benefit from using a camera with an APS-C sensor that will give you a native crop (and additional magnification).

While any camera can pair very well with an extension tube, crop sensor cameras with very good low light performance will work best. The Nikon D500, for example, is a great choice if you want great magnification.

Extension tubes can be an easy way to add macro capabilities to non-macro lenses or even to increase the amount of magnification that you get from your dedicated macro lenses. Because of the simple nature of an extension tube, there is little performance difference between different brands and models. Pairing an extension tube with the right lens can open up many possibilities for your photography.

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