An extension tube is a hollow tube that fits between your lens and the body of your camera. An extension tube is used to alter the MFD (minimum focus distance) of the attached lens. They allow you to focus on subjects that are closer to the camera and achieve greater magnification.

Images in this post use 85mm and 135mm lenses with 12mm extension tubes.

Gabby at home by Paul Sager, on Flickr


Lenses are designed to focus light to the specific distance where the sensor sits behind the lens. 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, the lens will be unable to focus on the subject as the point of focus falls behind the sensor. By moving the lens away from the camera body (and sensor), an extension tube adjusts the focal point of the attached lens. This allows you to focus on objects closer to the lens than you could otherwise.

Gabby at home


Unlike teleconverters, extension tubes have no optics in them at all. This means that in most circumstances, they have very little effect on image quality.

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 with one of those lenses, you can magnify those problems. Typically, macro lenses and 'portrait' lenses are very sharp and well corrected at their MFD.

Gabby at home


The minimum focus distance of the EF 85mm f/1.4L IS is 33.5-inches. I'd prefer a tightly cropped image that maximizes my 22MP and 24MP sensors, rather than cropping a large amount into the image. Calculating the new MFD with the 12mm extender can be done. For simplicity, let's say the MFD changes to about 18 inches as well as increasing the magnification. Essentially, I can now focus just on her face filling the entire frame.

Gabby at home


With an extension tube such as the modest 12mm, I have just minor or no cropping of my subject, meaning I can use all the pixels of the sensor. Or, like the extreme close-up above, I can focus as close as possible, then crop closer, and still have a highly detailed and screen-filling image from the remaining pixels.

Extension tubes work with any type of lenses: primes or zooms, portraits, and macro. Extension tubes are an inexpensive way to get the kind of short focusing distances typical of dedicated and much more expensive macro lenses.

Gabby at home


Images captured in this post use RAW and were processed in Adobe Lightroom v6. The 85mm lenses leverage IS and IBIS technologies, working at shutters as slow as 1/10 second while hand-holding the camera. The 135mm lens was reserved for brighter light as neither the lens nor the EOS body provide stabilization.

Gabby at home


These images are sized to fill your wide-screen display. Try using <F11> to maximize your browser window for the full effect. If the images overshoot your display, such as a laptop, just click on the image or the URL link and they'll resize to your screen from the host Flickr site. You can click a bit further into the image details on the Flickr page, if desired. EXIF data is available from the host Flickr pages as well. On the Flickr site, use your <L>key for Large and the <F11> for the full-screen.

Great post, Paul. Gabby is a beautiful cat!! This is a timely post for me, as I've been thinking about getting extension tubes. I was going to go with Canon (some reviews said they are a better fit), but they're quite a bit pricier. I was also trying to decide if the 25mm or 12mm would be best to start with. I was originally only thinking about macro work (flowers, snowflakes, etc), but I had also read about using them with wildlife photography. Do you have any thoughts or recommendations on brands or sizes for getting started?
Thanks,
Patty

Thank you Patty! I have both the EF25 and EF12. For Canon, they're intended for all of Canon's lenses, including the Great White L-series primes, so they're sturdy for sitting between these heavy lenses and the camera body. I started with the EF25 that is a great tool for a lens like the supersharp 135L making it a macro ish lens for flowers or specially the butterfly room, one of my typical uses. I've used the EF25 too a lot with the 70-200 f/4L for macro ish shots in the greenhouse / botanical garden. The EF12 was a later / recent addition, more for general purposes, letting specifically the 85mm lenses get closer to the subject.

When you say 'wildlife', I'm not sure that will work beyond small insects. While allowing the lens to focus closer, the tubes also disable the ability of the lens to focus at infinity. So, anything beyond the closest subjects cannot be focused at all with the tube installed.