What is a Extension Tube ?

by Vivek Doshi
1 comment
Extension tubes - Marco photography

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.

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

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. 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.
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.

Rose - Macro photography - Home photography idea
Close up of housefly - Macro photography

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.

 

How to choose 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 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
  • 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.

Pros and Cons of 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 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.
  • 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.

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1 comment

Hacks and DIY in photography - Lens Travelier Tips June 19, 2021 - 11:48 pm

[…] Macro lens are pretty expensive. One way to get around is to use Extension tubes. Extension tubes are a bit more technical than it seems. To simply this you can use a lens […]

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