How does AF-A actually work while shooting?

culturalproduct

Stupid sounding question but I can't seem to get AF A or AF C to work right. I rarely use AF so maybe I'm missing something.

I set my D7000 to AF-A, Auto, and also tried AF-A, 3D. I was expecting the camera to lock onto a subject, then actively re-focus as the subject moved. It focuses and then nothing happens when there is movement.

For ex., tried putting my cat at the other end of the dining room table, focused on his eye, and when he moved toward me, he just got blurry and the camera did not change focus.
I also tried focusing on a subject, then moving around myself, but again they just went blurry, camera did nothing.

I was interested in this focus mode for video mainly, so the camera would lock on a subject and track them while rolling. Couldn't get that to happen either, so tried using it for stills, as above.

Should the camera be actually re-focusing when the subject moves? Or have I misunderstood what it can do?

Thanks

PB_PM

Auto focus for video is not great to be honest, and no amount of settings will fix that.

culturalproduct

Thanks PBPM, I'm getting that, DSLR AF is never going to work like AF on a "real" video camera. What I'm puzzled about now is, when shooting for stills, why doesn't AF-A adjust focus as the subject moves - or have I misunderstood what Nikon means by tracking focus? I thought it was supposed to actually re-focus if the target point moved closer/away.

Ironheart

AF-C is what you want. AF-A is really shorthand for choosing between AF-C and AF-S. I'm sure that when you start focus on a static subject, AF-A will select AF-S, not C. Just put it on AF-C.

heartyfisher

I am not a video guy but from what I gather( and I can understand why), AF NEVER works well for professional video. All "real" video is done with manual focus. "Real" video cameras/setups makes it as easy as possible to do manual focus. So your understanding needs adjusting... ..

Having said that amateur video using the AF system is not bad and quite fun. You just need to know the limits and settings. You can do that while learning/improving your manual focus technique.

Re af-a, af-s and af-c. Af-A is really a combination of AF-S and AF-C. The camera tries to determine which mode you want ie its AF-S if YOU dont move your camera. its AF-C when you are moving your camera, chasing a subject. It cant start following a subject after its locked on with [AF-A/AF-S] mode. if you want it to start following the subject you can try to switch it back to [AF-A/AF-C] mode by moving your camera.. I set the modes depending on the situation. I use AF-A when possible (I also use P-Mode LOL !! ), but will switch to AF-S or AF-C when needed.

NSXTypeR

Usually I use AF-S mostly just because most of my subjects don't move... but mostly because I have yet to figure out the AF modes out of laziness.

spraynpray

I use AF-C for single shot macro since I got the 60mmG (after the D) because it can keep up. Stacking - either hand-held or slide mounted - is manual focus.

Nikoniser

AF-A just means that the camera chooses AF-S or AF-C ( called AF-F in live view in some cameras ) for you depending on it detecting movement on the subject when you focus on it. So if you are in AF-A and focus on your non moving cat, the camera goes, ok, subject not moving, I shall select AF-S mode.

This means that when the cat starts moving, you need to press the focus button again for it to detect the movement and *in theory* it should then keep focus on the cat.

It doesn't work terribly well, I prefer to manually select AF mode.

Live view autofocus on Nikon cameras is horrible, often inaccurate with fast glass, due to contrast only detection. The only Nikon camera to do it right is the Nikon 1 series which has dual pixel autofocus like canon and works brilliantly, this is why although I have D810, D7100 I use my Nikon 1 for Video work when light allows !!!