Contrast Detection AF

[Johnf]

Bob

Thanks for the article on the AF trick with teleconverters.  As usual you have a way of simplifying these things. 

I have heard that you can put a piece of tape on one of the contacts on the TC to avoid the reporting of max aperture of the lens + TC but this still relies on the phase contrast AF.  I have used a Tamron 2x with the canon 70-300 and it doesn’t work at all.  I have also used this TC with the Canon 100-400 and I actually occasionally get accurate AF under optimal lighting conditions but it is highly unreliable.  One way of incorporating your trick would be to set one of your custom settings to do live view with contrast detection AF (by the way is this under a custom function?).  Try the default method and if you are hunting, turn the dial to your custom setting and use the contrast detection AF.

On a side note, I find that I don't take many "Keepers" with this TC, I always find myself choosing a crop of one I took without the TC.  Are the optics of this TC poor quality?, (am I just a bad aspiring serious amateur photographer?), are the canon TC's better?

Thanks again for helping us use our cameras better

John F

[Bob Atkins]

I don't have a very high opinion of any 2x TC, especially on a slow zoom. You can get away with them on an excellent telephoto prime but that's the exception rather than the rule. It's just pushing things a bit too hard. Results with a 1.4x are usually much better.

I have the Canon 1.4x and 2x TCs, but it's very rare I reach for the 2x. It is usable with the 300/4L for example, but even then you really need to stop down a stop or more for best image quality. I seem to recall that f13 (true) gave the best results, which means the lens itself is at f6.3 (1.3 stops down from maximum aperture).

[Johnf]

Maybe I'll try a 1.4 next

Thanks