40D+1.4TC + 100-400AF

Is seems that AF doesn't work with my 40D + 1.4x TC with 100-400. Do others have this feature also?

But AF does work well with 40D+1.4TC+500. Is this because the 500/f4 is a faster lens or the AF system in the 40D?

Thanks

sagebrush wrote in post #6591145
Is this because the 500/f4 is a faster lens or the AF system in the 40D?

Yes. The AF on a 1D series would still work I believe.

On a 40D, you lose auto focus on lenses slower the 5.6. So the 500 f/4 w/ 1.4x TC gives you 5.6, so AF remains active. Where as on the 100-400 its 4.5-5.6, so adding 1.4 to this will be slower then 5.6, causing a loss of AF.

You could tape contact i believe to prevent the reporting of the aperture, but the AF may not be reliable.

On 1D series bodies they can AF up to f/8 if i recall.

Thanks all for you reply.....Sagebrush