Thursday, 17 July 2008

Canon extenders

Fortunately for my wallet I'm not into wildlife photography and so haven't needed to buy any of Canon's high performance telephoto lenses - here are the current prices at Warehouse Express: Canon 300mm f/2.8 L IS £2848, 400mm f/2.8 L IS £4889, 500mm f/4 L IS £4154, 600mm f/4 L IS £5399, 800mm f/5.6 L IS £9000! My longest lens is the 70-200mm f/2.8 L IS which suffices for all my professional wedding and portraiture work. However, I do occasionally need a bit more reach, and so to achieve this without breaking the bank, I invested in a Canon EF 2x II extender (also known as a teleconverter) - seen above next to a Canon EF 24-70 f/2.8 L lens for size comparison. It attaches between the camera and lens, and as its name suggests, it doubles the focal length range of the lens.

The downside is that the aperture of the lens is decreased by two stops, so my 70-200mm f/2.8 IS becomes a 140-400mm f/5.6 IS lens - image stabilisation is not affected. This is the smallest aperture at which autofocus can work on a Canon EOS 5D (1D bodies can handle f/8.0) - if your lens is slower than f/2.8, adding a 2x extender will require you to focus manually. This doubling of focal length results in a doubling of magnification - great for wildlife or, for example, photographing the moon, as above (cropped). As an aside, I shot this in manual mode in order to underexpose by 3 stops to take into account the black sky filling 60% of the image - exposure compensation only allows you to correct by -2 stops in aperture priority mode. The magnification resulting from the extender does lead to a small deterioration in image quality. Canon also sells a 1.4x extender.
I've used the Canon extender on all my lenses - it's particularly entertaining to stick it on a macro lens in conjunction with extension tubes (I'll discuss these in the next post) to achieve high magnifications.
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