NEX-6 photoshoot w/ Zeiss 24/1.8, SEL 50/1.8 and 16-50 kit lens (pics)

For a shoot like this when the subject is stationary, they're all fast. In a few instances my Canon 5DMKII would have struggled with heavily backlighted scenarios but I had the lighting scene yesterday and my NEX-6 performed admirably.

Having said the above, two weeks ago I did a shoot and I asked the subject to walk towards me with the NEX-6 and the SEL 50/1.8. During the first few frames the focus was locked in but it became out of focus as the subject closed in on the camera. Not sure if this is just a system limitation or I just need to learn the proper settings to get this right.