40D focus sensors

[Adey]

So the 40D apparently has 9 cross-type sensors, which when combined with a 2.8 lens results in better focusing performance. So how come when I use my Tamron 17-55 2.8 lens, the center focus point is still much better at focusing in low light than any of the outer sensors. Can anyone tell me why this is please?

Thanks

 

[travellingcello]

Because the middle focus point is more sensitive for lenses 2.8 and faster.

Check out your manual.

 

[Canon Bob]

So the 40D apparently has 9 cross-type sensors, which when combined with a 2.8 lens results in better focusing performance.

That's not quite how it is Adrian. The peripheral points are cross type but optimised for apertures at f/5.6. Only the centre point is optimised for f/2.8.

Bob

 

[Adey]

I see, thanks guys!