15 April 2009

Closer than the minimum focus distance

Extension tubeDo you ever hit the 'subject too close' limit with longer lenses? Wouldn't it be great if that 70-200mm lens with it's 1.2m closest focussing distance could be used even closer sometimes?

The EF12 II and EF 25 II extension tubes move the closest focus point of your lens even closer. Macro photography with an EF 500mm f/4L IS USM anyone?

Extension tubes are tools that some photographers see as only for macro work, but you can use them with a lot of lenses not just macro ones. Moving the rear of a lens further away from the sensor means that it will focus the light from closer subject distances than it can do normally, the downside - you can't focus on infinity anymore.

Some years ago Canon used to show a video with wildlife photographer greg Basco shooting snakes in trees using an EF 300mm f/2.8L IS USM lens with an extension tube on the back allowing much closer focussing.

In the past I've found the extension tube a neat solution to the problem of shooting through glass at zoos. In some cases you need to have the lens right up against the glass to reduce the reflection, but then the subject is too close for the minimum focus on the lens. Put on the extension tube and the problem is solved.
These two shots were taken with an EF 70-200mm f/4L IS USM lens at it's minimum focus distance, the first with the lens only, the second with an EF 12 II extension tube fitted between lens and camera.

200mm close focus 200mm close focus with 12mm extension tube

You can now focus at distances less than 1 metre from the subject but maximum subject distance becomes just less than 5 metres with the lens set to infinity.

When Canon introduced EF-S lenses with the EOS 300D it changed the extension tubes so that they could be used with EF-S lenses as well as EF lenses. This makes it possible to use an EF-S 18-55mm f/3.5-5.6 kit lens as a macro lens on an EOS-1Ds Mark III, but the subject distance is very short. Some wide-angle lenses aren't compatible with extension tubes as the point of focus moves to a point inside the lens itself.
For the technical or the inquisitive readers you can also combine extenders like EF 1.4x II or EF 2x II with extension tubes for even more magnification.
Extension tubes may make the automatic peripheral illumination correction available in DIGIC 4 cameras insufficient, and likely it will render flash distance information wrongly too.


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