31/03/09

Teleconverters are a useful way of increasing the focal length of a lens without too hefty a financial cost. They are mounted between the lens and the camera and typically increase the focal length by a factor of 1.4 or 2x. Canon call their teleconverters 'extenders'. Although cheaper than buying a longer lens, teleconverters tend to cause a degradation in image sharpness, contrast and chromatic aberration. The maximum aperture of the lens with which it is paired also suffers. A 2x extender will lose two stops of light so, for example, a f2.8 lens effectively becomes a f5.6 lens. Autofocus speed is also slightly affected.

This review for Canon's 2x converter is pretty similar to my review for the 1.4x converter. This is due to them being very similar products. The Canon extenders are more expensive than those from independent manufacturers but claim to be of exemplary standard. They are only compatible with lenses from Canon's L range and won't fit the less expensive ranges. Even with L lenses they will only fit some. Broadly speaking they are suitable for most L telephoto primes and telephoto zooms. A full list of compatible lenses can be found on the Canon website.

The 2x extender comes supplied with lens caps and a soft lens case. Unlike the Mark I version this one now has weathersealing rings which are effective when paired with 1 series camera bodies and other weathersealed lenses such as the 70-200 f2.8 IS. The build quality is superb - as expected from a product targeted specifically for use with L lenses.

I've tried the 2x extender with Canon's 200mm f2.8 L USM II prime lens and also with the Canon 70-200mm f2.8 L IS USM zoom. I've also used the Canon 1.4x extender with both lenses. With the 1.4x extender I find it really hard to see any significant change to the image quality compared to the lens without the converter. The results with the 2x extender are still very good but are noticeably worse than with the 1.4x. Not surprisingly the prime lens gives slightly better results than the zoom although you have to be very critical to notice. Consequently, I'm confident to use the 1.4x on the 70-200 zoom but tend to restrict the 2x extender to the 200mm prime when possible. I also compared the Canon 1.4x extender with a Sigma 1.4x converter. The Sigma wasn't the latest from that manufacturer but the results were very noticeably worse in all areas compared to the Canon.

So, in conclusion, a very useful tool for extending the reach of your telephoto lens at relatively low cost but for the best results it does need to be used with excellent quality prime lenses.

Overall Rating: 4/5
Ease of use: 4/5
Value for money: 4/5
Build quality: 5/5
Sharpness: 4/5
Autofocus: 4/5