Z8/9 Auto Focus (C) w/Sub Detection 🐦+👁️=🧐

[fcotterill]

Yes, all settings are optimized to maximize evf brightness - eg adjust for easy viewing (even tried starlight). Dynamic or single point mostly yield good focus. The issue being explored has to do with accuracy of focus with SR in lower light. It's not even the actual subject recognition, which the system does perfectly. It's that the subject it has recognized and put the AF indicator on winds up being out of focus and specifically focused on the opposite eye from where the AF box is located - even if you use the option to specify which eye it should focus on. The discussion of predictive tracking made the wheels really start turning to think if there is a connection.

I agree with @EricBowles about correct exposure in lowlight. This is crucial. In at least one of his columns, June 2022, Thom Hogan discussed this factor, with hypotheses about how Autofocus and Exposure are causally linked in the dual stream imaging of the Z9, via the EXPEED7. There's an older thread discussing the possibilities/implications.

The reasoning extended to a possible function of the Picture Control file ; that its sharpness becomes important in lowlight - IF - the Autofocus algorithms are analyzing jpg patterns in the dual stream processing.

Also see "Does the accuracy of Nikon's Z-system focus depend upon the amount of ambient light?"

With a Z8 or Z9, you could test for the effects of Subject Detection in low light with a 1*1 Custom Area mode. Toggle Subject Detection off / on with a RSF setting.

 

[fcotterill]

On Z9 Autofocus system, discussed in many earlier BCG threads....

From Thom Hogan Z9 ebook pg 670: Unlike the Nikon 1 and earlier Z MILC, Nikon "focus on. The more distinct the color/pattern is, the more likely that the Z9 follows it faithfully...."

If you have subject detection active, 3Dtracking adds this information, as well and so it sees all

three datasets [color - pattern - subject).

"...It appears that Nikon hasn’t 100% decided what to optimize in terms of the three detections, so you’ll see the focus system often changing the position when subject detection is enabled with 3Dtracking... 3D-tracking doesn’t require a human, animal, or vehicle and subject detection, though. I’ve seen it track frisbees, footballs, and other types of objects. And when the subject detection fails, which it does on some types of animals such as elephants, 3D-tracking can come to the rescue, particularly if you can get it honed in on a unique color/pattern...."

"... This mode is excellent for a number of different tasks, particularly when you’re photographing subjects that aren’t human, such as (supported) animal or vehicle. 3Dtracking works best if there is a unique and clear pattern, color, or subject the Z9 can lock onto..."

Auto AF Mode in Z9: pg 676: "...Auto-area AF —When subject detection is active, this mode is surprisingly good with both individual humans and animals when that subject is within the focusing frame (wide red bounding indicators). So when taking pictures of people or animals facing towards you this function works a bit like magic. Just be aware that with multiple faces, the camera is likely to first choose the closest, biggest, or the one with the most contrast, though you do have the option to override the camera’s decision..."

.... Subject detection is completely turned off, the more an area dominates the focus sensor area, the more likely the camera is going to pick it. Otherwise, the camera tends to pick closest recognizable object or a more contrasty object. I’ve had the Z9 correctly recognize the body of animal with subject detection off, but that’s usually when the animal’s color and shape are in high contrast to its surroundings...."

 

[Ken Miracle]

This generally works for wildlife shooting, but when one is in a situation where a flash is going to be used there are two problems with this.

The first is that the camera does not know or properly display in the EVF or the viewfinder what the exposure will look like with the flash. Actually, my understanding is that it might do this for a select handful of Nikon branded speedlights but even then it's pretty iffy as to how accurate it is. Meanwhile, for any 3rd party speedlights, off camera strobes, and even other Nikon branded ones it just doesn't work.

The second is that because of the fact that the evf is not being adjusted according to the anticipated effect of the flash, and because the camera will have it's exposure set to account for the flash, the EVF will display an extremely dark, even pitch black scene, and since this is what the AF system uses to focus, focus will become impossible.

No issue for me I have not used a flash since I switched to Z9, I never use one on wildlife and that is 90% of what I shoot so my speedlights and pocket wizards just sit in my dry cabinet I still do some indoor people stuff but in situations where I can not use flash.

What it does show you is what the ambient light will be without the flash. That would come in handy for fill outdoors.

 

[EricBowles]

Also see "Does the accuracy of Nikon's Z-system focus depend upon the amount of ambient light?"

I've tested this one pretty well with subjects such as a backlit bird with bright ambient conditions. If the subject is underexposed - even by just a half stop - Eye AF stopped working and the camera reverted to the body of the subject. In my case the correct exposure for tracking required overexposing the background - almost to clipping - so that I could properly expose the subject and clearly see the eye and markings on the head. I tested at a stop or less below the required exposure which was better for the background, and eye focus stopped working. My testing was at a distance where the subject was large in the frame and I had a clean background. The subject was a king rail - a reasonably large bird with contrasty markings on the head and a dark eye.

 

[fcotterill]

I've tested this one pretty well with subjects such as a backlit bird with bright ambient conditions. If the subject is underexposed - even by just a half stop - Eye AF stopped working and the camera reverted to the body of the subject. In my case the correct exposure for tracking required overexposing the background - almost to clipping - so that I could properly expose the subject and clearly see the eye and markings on the head. I tested at a stop or less below the required exposure which was better for the background, and eye focus stopped working. My testing was at a distance where the subject was large in the frame and I had a clean background. The subject was a king rail - a reasonably large bird with contrasty markings on the head and a dark eye.

Yes, your results concur with my general experience (Z9), although I haven't tested it properly.

For such subjects, this is where a Fn button dedicated for spot metering only would be useful, which is simple on the D500, D850 and also Z6 and Z7, but not Z9 nor D6! A RSF setup does work but wastes the setting for other situations.

 

[SCoombs]

Yes, as I said I know how it all works with regard to the importance of correct exposure in the viewfinder. I remember trying to tell people about this in the past but many wouldn't believe me until Thom Hogan wrote about it.

This is a big reason that many people use the "adjust for ease of viewing" setting in lower light, of the "apply settings to live view only when flash is not used" setting, because by definition when flash is used you're underexposing as far as the camera and evf are concerned.

 

[EricBowles]

Yes, as I said I know how it all works with regard to the importance of correct exposure in the viewfinder. I remember trying to tell people about this in the past but many wouldn't believe me until Thom Hogan wrote about it.

This is a big reason that many people use the "adjust for ease of viewing" setting in lower light, of the "apply settings to live view only when flash is not used" setting, because by definition when flash is used you're underexposing as far as the camera and evf are concerned.

That's a good point, Shane. When using those settings, it's easy to fall below the exposure level needed for subject detection/ eye detection. That's especially true when you desire a low exposure with a plan to boost it with flash or in post processing. That's a technique I often use for portraits - underexpose the scene and balance the subject exposure with flash.

 

[Ken Miracle]

I've tested this one pretty well with subjects such as a backlit bird with bright ambient conditions. If the subject is underexposed - even by just a half stop - Eye AF stopped working and the camera reverted to the body of the subject. In my case the correct exposure for tracking required overexposing the background - almost to clipping - so that I could properly expose the subject and clearly see the eye and markings on the head. I tested at a stop or less below the required exposure which was better for the background, and eye focus stopped working. My testing was at a distance where the subject was large in the frame and I had a clean background. The subject was a king rail - a reasonably large bird with contrasty markings on the head and a dark eye.

Pretty much the situation several times on every birding outing although mine are usually much smaller birds, yesterday Brown-headed Cowbirds and Lesser Goldfinches. The extent of plus ev dialed in depends on the contrast between the subject and the back ground. For me having the EV exposure compensation on the control ring on Z800 or on the focus ring Z180-600 makes it fast ... I just have to remember to dial it back down when I am done. I also use center weighted or spot metering frequently in those situations I access metering through my i menu and while quick it is not as fast as EV on a lens ring.

If I could predict this happening in advance or was shooting for art not ID I could set up with spot and probably even full manual well in advance and control exposure with ISO like I used to in the past when I used aperture priority on D300s etc.. before D4s introduced me to a much more effective auto iso