Definition: Macro tube(s); Extension tubes

Macro tube(s); Extension tubes

• Three electronically enabled macro extension tubes •
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The green pen shows that there are no lens elements in a macro extension tube.

The macro, or extension tube, is a way to perform macro photography (close-up photography). The tube extends the distance from the photographic lens to the image plane where the image is formed. In effect the macro extension tube is used to create a magnified image using an ordinary lens and tube. This removes the need to purchase a specialist macro lens.

As a lens is moved further away from the image plane (which is also the digital image sensor) the image gets larger on the sensor. This magnification is what creates the close-up aspect of the shot. Typically macro shots are approximately one-to-one correspondence from the subject to the image on the sensor. However, they are much larger when printed or rendered on a screen so they seem many times larger than real life.

Macro extension tubes are tubes that are fitted directly to the camera body at one end and mount the photographic lens at the other end. The insertion of the tube separates the lens elements from the body by the additional length of the extension tube. The tubes come in a variety of lengths depending on the desired magnification and the mountings. Typical lengths are from around 10mm to 30mm. There are no lens elements in macro extension tubes.

The use of macro extension tubes tend to reduce the intensity of light reaching the digital sensor because of the increased length. The macro effect also significantly reduces the depth of field. For this reason, as with a macro lens, use of high light levels, longer exposures and a tripod are advisable. Very close focus is difficult without a tripod.

Extension tubes can carry the electronic connections required to allow the user to use auto-focus, aperture control and any other electronic functions of the lens. These are at the higher end of the market.

Macro extension tubes are also available as simple tubes with the appropriate mounting screws to fit to the camera and lens. Typically these are much cheaper than brand-designed extensions. They function just as well as the electronically functional designs but the lens will need to be focused manually. As macro shots normally involve a very shallow depth of field the use of manual focus is desirable in any case. Auto-focus is difficult to get absolutely right in a very shallow depth of field. So it is an advantage to focus with manual dexterity.

Using a non-electronic macro tube may mean that your lens will only set the aperture at its widest opening. This may further impact the shallow depth of field. Some lenses allow you to set the aperture before you insert the extension tube. In this case you can set up the appropriate aperture before fitting the extension tube.

As with a macro lens, the use of macro extension tubes allow you to get close to the subject. It is common to be able to work at around 300mm from the subject. However, the actual work distance is dependent on which lens you are using with the macro extension tube and the length of the tube itself.

Macro extension tubes (without electronics) can be an inexpensive purchase. They are very good for learners to come to terms with the different techniques involved in macro photography without the expense of buying a specialist lens. For just a few Pounds or Dollars these can prove an invaluable asset in your kit bag.

Canon Macro extension tubes:
Macro extension tubes are an inexpensive way to explore macro photography… Macro Extension Tube Ring For CANON EOS 5D /II/III, 7D, 40D, 50D, 60D, 450D, 500D, 550D, 600D, 650D, 1000D, 1100D, 1D Mark II , 1D Mark III , 1D Mark IV, 1DX