Extension Tubes for Macro Photos

Extension tubes provide (for some people) an attractive way of adding a Macro capability to their camera set up. Extension tubes are available for almost every SLR body, can be attached to different lenses for different effects, and are much, much less expensive than dedicated macro lenses. I know that Canon and Nikon both make extension tubes for their cameras and I know that Kenko makes extension tubes for almost every SLR brand. The Nikon School plugged extension tubes as a reasonable alternative to macro lenses so I went that way. I have been learning about the peculiarities and limitations of extension tubes for several days now and wanted to share some of the things I've learned.

Extension Tubes, Tele-Extenders, and Tele-Converters

First of all, let me clear up a misunderstanding that some people have. An extension tube is very, very different from a tele-extender or tele-converter and serves a very different purpose.

A teleconverter is designed to increase the apparent focal length of a lens. For example, in the Canon system, a 135mm lens can become 189mm or 270mm lens with the addition of the proper teleconverter. This increased focal length comes at the cost of speed of the lens, in the previous example, the f2 135mm becomes an f2.8 or an f4 when the teleconverter is attached. An extension tube is designed to increase image size on the film or sensor so that macro / extreme close up photos can be taken. This capability comes at the cost of stand off distance, more on this later.

I got the Canon extension tube EF25. It works nicely on 3 of my lenses. The EF25 is not compatible with my 20mm lens. In fact the 35mm lens is the shortest lens that is compatible with the EF25 although the EF12 will work with the shorter lenses. I chose the EF25 for two reasons: 1. It was locally available, 2. It provided greater magnification. On the 50mm lens it can provide magnification up to .68X (a full life size reproduction would be magnification of 1.0X.)

Here is what the extension tube can do:

50mm lens at closest focus point

50mm lens with extension tube attached (.68X rating)

85mm lens at closest focus point

85mm lens with extension tube attached (.44X rating)

300mm at closest focus point (.25X inherent capability)

300mm lens with extension tube attached (.39X rating with extension tube)

You may have noticed that the longer the lens, the lesser amount of magnification the extension tube gets you. This is because of how an extension tube works. Every lens has a minimum focus distance as part of it's characteristics, for example my 50mm lens has a minimum focus distance of 1.5ft, the 85mm - 2.8ft and the 100-300 - 4.9ft. (In general, the longer the focal length of the lens the greater the minimum focal distance.) An extension tube radically reduces that minimum focal distance. In fact it creates a focus zone, a fairly narrow focus zone, within which an object may be in focus. For example on the 50mm lens the minimum focus distance is reduced down to about 4 inches and the depth of field becomes so narrow that you'd best be pretty close to that distance when you attempt to focus the shot.

This fact is why the 25mm extension tube won't work with anything shorter than a 35mm lens because the focus zone is moved in so close the front glass element on the lens prevents you from getting that close.

Depth of Field (DOF)

Also, as you get closer to the focus object the Depth of Field (DOF) gets very narrow (see DOF tip). This requires some very precise work to get your entire subject in focus with the extension tube mounted on the shorter focal length lenses. But increasing the f stop will increase the DOF just as always.

200mm at f 5.6

200mm at f32
Differences in the appearance of the flower are due to differences in processing, not a function of f-stop change


I'm happy I got the extension tube. It greatly enhances the capability of the lenses I already have and gives me some degree of Macro capability. The extension tube will work well on the 50mm lens for macros of still life and inanimate objects but it is difficult to use on living things that might notice and object to your presence since you have to get so close.

Hint: if trying to shoot bees with the 50mm lens and the extension tube take your lens hood off. That won't intimidate them so much and they won't so readily fly away or attack.

The extension tube works great for moving nature shots on the longer lenses because they have a much greater "stand-off" range, something measured in feet rather than inches.

A Kenko 25mm extension tube can be purchased for around $70.00, the Canon is about $120.00 both contain the same low dispersion air.

If you have any questions or suggestions about this tip please contact me by email.