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Have you ever found yourself wanting to focus closer to your subject and reaching the limitations of your lens's minimum focusing distance (MFD)? If so, you know how frustrating it can be seeing your tiny subject in the middle of your frame and having to crop afterwards. Fear not, extension tubes are a relatively inexpensive way (less than $100) to getting started and taking your macro photography further!
Photo by resakse
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There are two ways to focusing closer to your subject. The first is a close-up filter that screws onto the front of your lens. These come in a variety of diopters +1 through +10 and different filter thread sizes. They are a little more convenient than extension tubes in that you just screw them on, but the main drawback is the degradation of image quality. Because you are adding extra glass elements in front of your lens, image quality suffers and you will see soft images and chromatic aberrations. I would advise against using close-up filters.[inlineImage||||]
The second and recommended way to focus closer is to use extension tubes. They are hollow tubes (as the name implies) that fit between the camera body and your lens. They are mount specific so you will need to purchase a set that fits your camera. Some tubes have electrical contacts to enable auto-focusing which can be helpful, but quite limited in the macro range. They are also more expensive. Without contacts, you will have to focus manually (by moving closer or further away from your subject).
Photo by Thomas Shahan
What about teleconverters/extenders?
Teleconverters (1.4x/1.7x/2.0x/3.0x) do not allow you to focus closer. They increase your lens's focal length by the multiplier and thus increase your magnification. The lens's MFD will not change. For example, if you have a 100mm 1:1 (life-size) macro lens with a MFD of 12 inches and you add a 2.0x teleconverter, you will have a 2:1 (2x) magnification at 12 inches.
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How Extension Tubes Work
An extension tube works by moving the lens further away from the camera's image plane (sensor). The further the lens is moved from the camera, the greater the magnification and light loss (which you will need to compensate for with a longer shutter speed or artificial light). The more tubes you stack, the closer you can focus.
So all I have to do is stack a bunch of tubes and I'll be good to go, right? There must be a catch you're thinking! Well, yes. With an extension tube, you lose the ability to focus at infinity because of how the optics of a lens work. Extension tubes are strictly only for close-up work and can be used on virtually any lens, including telephoto zooms.
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What Lenses Work Best With Extension Tubes?
Sharp lenses with wide apertures (F/2.8 or larger) work best with extension tubes. Because you are magnifying your images, it helps if the lens is already sharp and a wider aperture will help you collect as much light as possible.
50mm Prime Lenses - "Nifty-fifty" prime lenses are cheap and extremely useful for a wide range of subjects. A stack of extension tubes on such a lens can allow you to get extremely close and still have stunningly sharp pictures.
Macro Lenses - If you want to go beyond 1x magnification, an extension tube and/or teleconverter is the best way to achieving 2x+ magnification for double, triple, and beyond life size!
F/2.8 Zoom Lenses - Some of these lenses have small magnifications and long MFDs so an extension tube will allow you to be closer to your subject should the occasion arise.