Aperture

Buying a macro lens can be expensive (especially a real macro lens such as MP-E 65 for EF Canon EOS bodies). Fortunately there’s the cheap alternative: macro extension tubes. With 100 EUR you can actually have 3 of different sizes which can work independently or together. That’s the case with Kenko Automatic Extension Tube Set DG:

Fig. 1: From left to right: 1 – 12mm tube; 2 – 20mm tube; 3 – 36mm tube.

Extension tubes are to be mounted between your camera body and the lens. What they actually do is to physically modify your minimal focal distance, thus allowing you to get closer to your subject by moving the lens away from your camera, resulting in a magnified frame.

As auto focusing is not a requirement in macro photography, electronic control of the aperture blades is important, that’s the reason you should aim for extension tubes with electrical connectors, as all modern EOS and Nikon lenses rely on your camera body to change aperture values.

Another cool thing about electrical connectors on extension tubes is that your camera can still use the autofocus (sort of…). Currently there is no Kenko version with EF-S lens compatibility. Canon does that for a higher price tag of course.

Another thing worth mentioning the excellent build quality of Kenko tubes. Also available the Nikon Nikkor AF /F-mount / D version.

There is always a trait when you attach accessories between your subject and the camera sensor, so, in this case, what you will lose is:

• ~1 f-stop for each extension tube connected to the camera, resulting in 3-4 f-stop drop if you decide to use all 3 at once. Drop in f-stops is caused by small amount of light dissipating inside your extension tube before it reaches the sensor. Therefore is best to use them with a fast prime lens such as the 50mm f1.4 or f1.2 L. Why prime? Because using extension tubes on zooms is not that efficient. Why 50mm? Because of “normal”, 50 degree view angle and minimal perspective distortions. To compensate for the f-stop drop, you have to move up the exposure time, thus in uncertain light conditions, a tripod is a must.

• ability of infinite focusing, as the focusing range will be limited to only a few centimeters.

• ability of autofocus if more than one ring will be connected. This also depends on the light conditions, and your camera body (but I assume not many 5D or 1D Mk II/III owners out there), but you’ll usually find your camera focus hunting, so switch to manual.

• additional thing to carry, bulky design. If you connect all 3 extension tubes from fig. 1 the space occupied is on par with a wide zoom (more or less).

What you’ll gain: a new world…

For these shoots the 50mm f1.4 was used with each and all extension tubes. The images below will speak for them selves.

Fig. 2: original image taken with the 50mm. Focus set to manual, minimum range (45cm)

Fig. 2.1: original image taken with the 50mm (100% crop)

Fig. 3: 12mm extension tube connected. Manual focus, minimum range. Nearest focusing point is now at 18.7cm, therefore the image has a magnification factor of 1:2.74, which is nice, but not a real macro (1:1 magnification factor).

Fig. 3.1: a 100% crop from Fig. 3… That’s a huge rice grain…

Fig. 4: 20mm extension tube connected. Also manual focus, lens set to minimum focus range. Nearest focusing point decreases to 14.5cm. Magnification ration is 1:1.9

Fig. 4.1 100% crop from above image. Hold the camera very steady at this distance as things like mirror movement or sudden reflexes of a black cat running through the tripod’s legs that can blur the image.

Fig. 5: 36mm extension tube. Again manual focus, minimum focusing range. This time, the uncropped image is starting to look like a real macro. Here, the nearest focusing point is only 11cm and the magnification ratio is 1:1.2

Fig. 5.1 Check out this baby! There is no way in telling if those are rice grains or mosquito eggs magnified using a microscope.

Fig. 6: 12mm, 20mm & 36mm extension tubes connected together. THIS is a real macro shot. The nearest focusing point is now at only 8.5cm. The magnification ratio is 1:0.68, which mean more power than any stock macro lens (except of course the MP-E 65 with 1:0.20 (5x real life size). As you see, now a single rice grain fills the entire frame. To get the difference, mouse over the image for the original version.

Fig. 6.1 For 100% crops at this magnifications you may consider using proper lighting conditions and L grade lenses because chromatic aberrations start to be visible even from tiny reflective surfaces.

What is also good with the extension tubes is that you will not lose picture quality as no additional optic element is introduced besides air Another option is to go for attachable close-up lens such as the 500D or 250D (Diopter) from Canon. The good with the close-up lens is that you’ll not lose infinity focus, occupies less space and can be used with EF-S lenses. The bad: additional optical element, far from packing the same power: only 1:4.2 for 500D and 1:2.8 for 250D which is the equivalent of one 12mm extension tube.

Extension tubes are the cheapest way to the fascinating world of macro photography. Keep exploring and you’ll be amazed by the outcomes.

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