# canon EF to EF-M adaptor - Phase detection AF



## WorkonSunday (Feb 29, 2016)

I don't think i found much information on the internet with regards which lens offer full phase detection support and which only uses contrast detection. 

my M3 is japan sourced, so i far i tried:

17-40mm F4 L
24-105mm F4 L
70-200mm non-IS L
Tamron 17-50mm F2.8 VC. 

from my experience, the 17-40mm, 24-105mm and Tamron can offer full phase detection AF. in fact 24-105mm AF was fast enough to track large bird in flight. 

The 70-200mm however only restrict to contrast detection. both 24-105 and 17-40mm are also F4 lens, so it should offer the same light to the AF sensor (unless this is transmission dependent), but the 70-200mm seems to only offer contrast detection. Any idea what is the criteria for phase detection?


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## Warren21 (Mar 25, 2016)

How can you tell which is using which?


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