rdrechsler Loc: Channel Islands Harbor, CA

I have a question I hope someone can answer. The D850 has, at least I thought, only 2 focus modes, single and continuous. I access them by pressing the AF/M button and turning the main dial. However, many, many times, I get 2 different settings: AF-S and AF-F. I can't find a good answer is to what AF-F is and why I'm not getting AF-C, which is what I want. Can anyone explain this for me please?

cameraf4 Loc: Delaware

The guru for the Nikon Focusing System, I would say, is Steve Perry of Backcountry Gallery fame. He's a member here and also has written a book on the system.

via the lens Loc: Northern California, near Yosemite NP

Are you trying to set this while in viewfinder mode? I think my D800 says AF-F in viewfinder mode. That's all I can offer as I don't have the D850. Steve Perry is great.

Steve Perry Loc: Sylvania, Ohio

AF-F is a Live View AF mode. It's basically like AF-C for Live View. Here's an excerpt from my book, Secrets To The Nikon Autofocus System, that explains it:

AF-F
Next, we have the AF-C Live View doppelganger, AF-F (Full-Time Servo AF). This is very similar to AF-C and will continuously try to focus on whatever is under the sensor. The difference is, it does this without any intervention from you. When you select this mode, it will immediately start rattling your focusing ring, desperately grasping at anything under the current AF area. No encouragement from your index finger or thumb is required to make this happen.

However, if you would like it to stop focusing for a minute and lock in at a certain distance, that's when you press your AF button (shutter release half-press, AF-On, etc.). It’s the opposite way we do viewfinder AF, so you’ll need to “think backward” I suppose.

All that said, keep in mind that although AF-F is a continuous mode of sorts, AF-C has nothing to worry about when it comes to tracking. AF-F can be used to maintain focus on a target, but it’s not in the same league as our viewfinder based AF-C (it’s like a lawn tractor taking on a Corvette). Your camera does feature an AF-F tracking mode that we’ll talk about shortly, just keep your expectations low.

Many video shooters find that AF-F works well enough to follow slow moving subjects across the screen as they shoot, so if you’re using your DSLR as a video camera, this is probably the mode you’ll end up using anytime you have something or someone wandering around your frame. Just keep in mind it’s a bit “jittery” and it’s easy to pick up that noise with your audio equipment. (Plus it can potentially look weird in the video.)

I hope that helps :)

Tronjo Loc: Canada, BC

AF-F is available in live view mode only and is similar to the AF-C in viewfinder mode. There is a difference between AF-F and AF-C modes: In AF-F mode the camera will try to focus on the selected area without any user interaction and will lock focus on half-press of the shutter button (or BF button); In AF-C mode it is the other way around - the camera tries to focus all the time when the shutter button is half-pressed (or BF is pressed) and will lock focus when the button is released.
Since I use Live View only with AF-S mode, I hope I got it right about AF-F :)

rdrechsler Loc: Channel Islands Harbor, CA

Thanks Steve, I bought your book a few days ago but have been too busy to dig into it just yet, so I appreciate the information. That makes sense. I usually shoot using the viewfinder, but the situation that arose was a very low light opportunity to shoot a great blue heron. The camera focused perfectly using AF-F, but it was pretty hard to view the scene through the viewfinder, so now I understand the difference. Great help!

rdrechsler Loc: Channel Islands Harbor, CA

Thanks Steve, I bought your book a few days ago but have been too busy to dig into it just yet, so I appreciate the information. That makes sense. I usually shoot using the viewfinder, but the situation that arose was a very low light opportunity to shoot a great blue heron. The camera focused perfectly using AF-F, but it was pretty hard to view the scene through the viewfinder, so now I understand the difference. Great help!

Steve Perry Loc: Sylvania, Ohio

Happy to help :)