01-22-2012, 09:20 AM
(This post was last modified: 01-22-2012, 09:24 AM by Brightcolours.)
[quote name='Klaus' timestamp='1327223375' post='15121']
Yes, the CAF on (all) DSLRs (in LiveView mode) is dismal compared to the "native" CAF on mirrorless cameras (with dedicated lenses). The technical reason is a bit of a mystery to me. Maybe it is because DSLR lenses receive the command to move to X whereas mirrorless system receive a continuous move command till focus is reached ? The command translation may result in less-than-optimal speed then. The screw-driven AF lenses should have an advantage in this case though.
The Leica 14-150mm (on MFT via adapter) is a counter argument to a certain degree - it is "fairly" fast.
[/quote]
The reason indeed is the motor and electronics implementation. PD-AF lenses are designed to move quickly a certain distance, and get new commands on their way there (PD-AF sensors can work no matter how fast the lens' focus is moving). Contrast detect AF works with making very small steps in quick succession. If you designed a lens for PD AF it does not necessarily work in an optimized way with Contrast detect AF. Of course, one could design lenses to be efficient with both, but DSLR lenses were never designed that way.
Yes, the CAF on (all) DSLRs (in LiveView mode) is dismal compared to the "native" CAF on mirrorless cameras (with dedicated lenses). The technical reason is a bit of a mystery to me. Maybe it is because DSLR lenses receive the command to move to X whereas mirrorless system receive a continuous move command till focus is reached ? The command translation may result in less-than-optimal speed then. The screw-driven AF lenses should have an advantage in this case though.
The Leica 14-150mm (on MFT via adapter) is a counter argument to a certain degree - it is "fairly" fast.
[/quote]
The reason indeed is the motor and electronics implementation. PD-AF lenses are designed to move quickly a certain distance, and get new commands on their way there (PD-AF sensors can work no matter how fast the lens' focus is moving). Contrast detect AF works with making very small steps in quick succession. If you designed a lens for PD AF it does not necessarily work in an optimized way with Contrast detect AF. Of course, one could design lenses to be efficient with both, but DSLR lenses were never designed that way.