8 December 2008

Canon cameras need f/5.6 or faster lenses

If you have a Canon EOS digital SLR camera that's not an EOS-1D or EOS-1Ds model you really should make sure your lenses have a maximum aperture of f/5.6 or faster. Canon doesn't write this in big enough letters in their specifications and instruction books but for the AF to work as Canon intended it needs a certain amount of light, the amount being the same amount as you get through a lens with an f/5.6 or faster aperture.

I've heard a number of photographers in camera clubs saying that they have focus trouble with their Canon cameras and their third party lenses. I also hear that it gets worse the more they zoom in with their lenses. The usual culprit is the Sigma or Tamron 18-200mm f/3.5-6.3 lens, though sometimes it's the Tamron 28-300mm f/3.5-6.3. The key being the f/6.3 aperture at the longer end of the zoom range. Last time I checked in a camera store the Sigma 18-200mm goes to f/6.3 around 120mm.

For a long time there's been no Canon 18-200mm solution but the new Canon EF-S 18-200mm f/3.5-5.6 IS USM is getting some nice comments [dpreview.com forums] [ Digital Pro Talk], and note that it's f/5.6 at the long end so your EOS will do it's best to AF properly, and we're not just talking in low light but in all kinds of light.

Check the current line-up of Canon lenses there's not a single lens with a maximum aperture slower than f/5.6 - says something doesn't it.

EOS-1D guys don't worry your center AF point can focus at f/8 so if you want to put a 1.4x extender on the EF 800mm f/5.6L IS USM lens you can still get AF.


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