Auto-focus question

[hank970]

I flew my Air 3 not long before sunset yesterday over some complex terrains -- lots of still-brightly illuminated, elevated rock formations separated by deeply shaded clefts. Rather than manually selecting focus points on the screen, I relied on autofocus, and results were almost uniformly disappointing -- properly exposed but out of focus. I was shooting at ISO 400 with an exposure bias of -0.7, and shutter speeds were in the 1/2000-1/4000 range, depending on whether I was using the 24mm or 70mm camera, so there was obviously enough ambient light for photography. I now suspect that focus was adversely affected because, when I composed my shots, shadowed areas were often located in the middle of the frames.

Does anyone know the what the default protocol is for autofocus? I might have assumed (or maybe hoped) that the cameras would seek to focus on the most contrasty object in the frame, but that's apparently not the case. When set for autofocus, without any overriding manual inputs, are the cameras programmed to focus only on whatever occupies the center of the frame?

I could find no information the operator's manual or in this site's search function which addresses this topic.

 

[Felix le Chat]

The default with newer drones is PDAF (Phase Detection Auto Focus), which is supposed to be more accurate with low contrast situations (low ambient light plus deep shadows) but I've found it to be the opposite on quite a few occasions with medium to low ambient light. If given a choice (which DJI never does), I'd have stuck with CDAF (Contrast Detection Auto Focus)

 

[hank970]

The default with newer drones is PDAF (Phase Detection Auto Focus), which is supposed to be more accurate with low contrast situations (low ambient light plus deep shadows) but I've found it to be the opposite on quite a few occasions with medium to low ambient light. If given a choice (which DJI never does), I'd have stuck with CDAF (Contrast Detection Auto Focus)

Thanks for your response. In auto mode, absent any manual selection, is PDAF operable over the entire frame or only in the center of the frame?

 

[Felix le Chat]

I really have no idea what the sensor architecture is, but the distribution of masked sensels won't be anything like the layout on a reflex DSLR CMOS, it's probably closer to that of a phone camera sensor with the same inherent problems... Small sensor + small photo sites = more sensor noise and limited contrast range in less than ideal light.

Occasionally, I take oblique night shots of motorway interchanges and the only way I've found of almost guaranteeing sharp focus is by engaging manual focus and racking for infinity.