My Z8 focus limiter deep dive

I was posting my focus limiter observations in the generic FW 3.0 thread but that has filled up and I have new observations so I'll post them all in this thread. Here's everything I know so far:

Limiter Setup

• Use AF-ON / Shutter half-press to have the camera engage the focus system over the displayed AF point to automatically calculate the near/far distance respectively. The camera uses AF-C for these focus operations, so either use the largest aperture your lens supports or turn on Maximum Lv Aperture setting to reduce the jitter/error-margin in the camera's distance calculation.
• You can tweak the limiter distance by using the rear-dial (near) or front-dial (far). It applies distance increments of 0.1m for every click of the dial up until 20m, then 1m increments until 50m, then 5m increments thereafter
• You can set the limiter distance manually via the lens focus ring by holding down AF-ON (close) or half-press shutter (far) while turning the focus ring. This will move the focus of the lens, setting the on-screen distance accordingly. Note that this may be preferable to using the dials because it accounts for the lens-specific distance reporting of the focus elements, whereas the dials don't. For example, as most lenses move toward infinity, the gaps in their focus distance grow pretty large, so using the dials may set a distance precision the lens doesn't actually support

Assigning Focus limiter to a custom control

• You can assign a control to the focus limiter option. This is preferable to menu diving because when assigned, the control has two roles - a short-press to toggle the limiter on/off, and a long-press to re-open the focus limiter configuration if you want to change the defined range.

Misc Limiter Notes

• The limiter is lens-specific, so the limiter configuration is automatically reset to NIL when you switch lenses. It does not reset when adding or removing a TC
• For lenses with limiter switches, you must set the lens to "full", otherwise the Z8's limiter is disabled

Support for 4 separate limiter ranges

• You can set 4 unique focus limiter distances by using custom settings banks (A-D), then switch between them by setting a Fn/control to "Access My Top Menu" and setting the top My Menu item to the Custom Settings Bank setting. In other words, the camera includes the a16 focus limiter setting in the bank-specific settings.

Limiter supported distances

• Each lens has a unique range of minimum and maximum focus distances it supports in the limiter configuration. For zoom lenses, the range is different at different focal lengths. Any distance outside the lens's supported range is displayed in yellow in the limiter configuration screen.
• Minimum Limiter Distance: Through trial and error I determined that the minimum limiter distance corresponds to the lens's MFD (minimum focus distance). Note that the increments in the limiter distance are 0.1m on the low end, so there will be some rounding here - for example:
  • On my 24-120Z, the minimum limiter distance is 0.4m, ie 0.3m is yellow and 0.4m is white. Nikon's specs for the lens say its MFD is 0.35m
  • On my 105Z macro, the minimum limiter distance is 0.3m, ie 0.2m is yellow and 0.3m is white. Nikon's specs for the lens say its MFD is 0.29m
• Maximum Limiter Distance: This appears to correspond to the helicoid resolution, ie resolution per click of the focus ring. As the lens approaches MFD, the jumps in calculated distance become much larger. The maximum limiter distance appears to correspond when this resolution drops below a certain threshold, which roughly corresponds to when DOF is much larger. Here is where the limiter distance turns yellow for various focal lengths on my Z 24-120 f/4.
  • 24mm 7.3m
  • 35mm 10.3m
  • 50mm 15.1m
  • 85m 26m
  • 105mm 32m - Note: My 105Z macro turns yellow at 32m as well
  • 120mm 37m

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Horshack said:

I was posting my focus limiter observations in the generic FW 3.0 thread but that has filled up and I have new observations so I'll post them all in this thread. Here's everything I know so far:

Click to expand...

Thanks for this!

Horshack said:

Misc Limiter Notes

• The limiter is lens-specific, so the limiter configuration is automatically reset to NIL when you switch lenses. It does not reset when adding or removing a TC

Click to expand...

Does the limit set for a lens re-engage if I set it, switch to a different lens, then switch back?

Horshack said:

• For lenses with limiter switches, you must set the lens to "full", otherwise the Z8's limiter is disabled

Click to expand...

That makes sense to me.

Horshack said:

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

I wouldn’t expect the detection system to work hand-in-hand with this limiter function. To me, focus distance limits help keep the camera from hunting so much. They aren’t there to help find particular things - that is already handled by the detection system. So … algorithmically:

For times I know my subject will be no nearer than X and no further than Y, don’t let the camera attempt to focus outside that range. This function shall override other focus-related mechanisms, so if for example the camera is set to bird detection and the detected bird comes closer to the camera than the minimum focus distance set, allow focus on the bird to be lost. Continue tracking the bird as possible, and it returns to a distance within the focus limits, focus on it again.

Right?

Horshack said:

I was posting my focus limiter observations in the generic FW 3.0 thread but that has filled up and I have new observations so I'll post them all in this thread. Here's everything I know so far:

Click to expand...

For starters, thanks a bunch for this. Very useful!

Horshack said:

Limiter Setup

• Use AF-ON / Shutter half-press to have the camera engage the focus system over the displayed AF point to automatically calculate the near/far distance respectively. The camera uses AF-C for these focus operations, so either use the largest aperture your lens supports or turn on Maximum Lv Aperture setting to reduce the jitter/error-margin in the camera's distance calculation.
• You can tweak the limiter distance by using the rear-dial (near) or front-dial (far). It applies distance increments of 0.1m for every click of the dial up until 20m, then 1m increments until 50m, then 5m increments thereafter
• You can set the limiter distance manually via the lens focus ring by holding down AF-ON (close) or half-press shutter (far) while turning the focus ring. This will move the focus of the lens, setting the on-screen distance accordingly. Note that this may be preferable to using the dials because it accounts for the lens-specific distance reporting of the focus elements, whereas the dials don't. For example, as most lenses move toward infinity, the gaps in their focus distance grow pretty large, so using the dials may set a distance precision the lens doesn't actually support

Assigning Focus limiter to a custom control

• You can assign a control to the focus limiter option. This is preferable to menu diving because when assigned, the control has two roles - a short-press to toggle the limiter on/off, and a long-press to re-open the focus limiter configuration if you want to change the defined range.

Misc Limiter Notes

• The limiter is lens-specific, so the limiter configuration is automatically reset to NIL when you switch lenses. It does not reset when adding or removing a TC

Click to expand...

This is weird and makes little sense in the real world. If I want to use the limiter but need to change lenses, it should stay put.

Horshack said:

• For lenses with limiter switches, you must set the lens to "full", otherwise the Z8's limiter is disabled

Support for 4 separate limiter ranges

• You can set 4 unique focus limiter distances by using custom settings banks (A-D), then switch between them by setting a Fn/control to "Access My Top Menu" and setting the top My Menu item to the Custom Settings Bank setting. In other words, the camera includes the a16 focus limiter setting in the bank-specific settings.

Limiter supported distances

• Each lens has a unique range of minimum and maximum focus distances it supports in the limiter configuration. For zoom lenses, the range is different at different focal lengths. Any distance outside the lens's supported range is displayed in yellow in the limiter configuration screen.
• Minimum Limiter Distance: Through trial and error I determined that the minimum limiter distance corresponds to the lens's MFD (minimum focus distance). Note that the increments in the limiter distance are 0.1m on the low end, so there will be some rounding here - for example:
  • On my 24-120Z, the minimum limiter distance is 0.4m, ie 0.3m is yellow and 0.4m is white. Nikon's specs for the lens say its MFD is 0.35m
  • On my 105Z macro, the minimum limiter distance is 0.3m, ie 0.2m is yellow and 0.3m is white. Nikon's specs for the lens say its MFD is 0.29m
• Maximum Limiter Distance: This appears to correspond to the helicoid resolution, ie resolution per click of the focus ring. As the lens approaches MFD, the jumps in calculated distance become much larger. The maximum limiter distance appears to correspond when this resolution drops below a certain threshold, which roughly corresponds to when DOF is much larger. Here is where the limiter distance turns yellow for various focal lengths on my Z 24-120 f/4.
  • 24mm 7.3m
  • 35mm 10.3m
  • 50mm 15.1m
  • 85m 26m
  • 105mm 32m - Note: My 105Z macro turns yellow at 32m as well
  • 120mm 37m

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

Ouch. This almost renders it useless for me. I can only help that "appears" means you're not certain and there's a chance it still does limit the AF when using subject detection. I switch subject detection off at times, but in situations where I might use a limiter (hide shooting and similar), it remains very useful.

Horshack said:

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

Indeed, subject detection work at any distance as long as the subject can be recognised by the AF detection system, but, to try to go further, what I tested with Focus Limiter On and AF-ON only :

- while pressing AF-ON button, if subject is out of the range defined with focus limiter feature and too blurry to be recognised, the camera won't even care - and won't try to focus on it at any time, of course - as usual

- the camera will only focus when the detected subject enters the range defined with focus limiter feature, even if it recognised the subject before it enters the range

- the camera won't allow you to shoot if you keep AF-ON pressed (I don't use standard shutter release button for AF) and nothing is in the range, whatever "out of focus release" setting is set to => it looks Focus Limiter has its own behaviour for that

- the camera will allow you to shoot if you use manual focus (or simply release AF-ON from the start) at any distance or if a previous subject was in focus after AF selected it and then you release the AF button, even if nothing is still in the range or really in focus (because you or the subject moved, for instance).

So there is potentially a benefit, even more if you set "out of focus release" to "Disable", because, of course, camera will only allow you to take the picture if you're in focus, whatever are other conditions.

Now it's a long explanation to say that in fact, focus limiter seems to work exactly as if you simply have control over the lens focus capabilities, because without focus limiter, you can see the same behaviour depending on the fact you're too near for your lense to be able to focus or not... which could be seen as intended and quite logical.

Also, I may be wrong but "Subject Detection" only sets a priority, so if anything is in focus, it will behave the same as if a subject is.

lokatz said:

lokatz said:

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

Ouch. This almost renders it useless for me. I can only help that "appears" means you're not certain and there's a chance it still does limit the AF when using subject detection. I switch subject detection off at times, but in situations where I might use a limiter (hide shooting and similar), it remains very useful.

Click to expand...

I just experimented.

I set subject detection to humans and then set distance limits from 0.7 to 1.7 meters. Then I displayed a picture of a human face on my computer monitor.

Then I moved the camera from inside (closer to the subject), to within, to outside the limits. Regardless of distance the camera still detected the face, and kept the focus box on the face, but it stopped attempting to focus at the limits.

This is exactly how I expect the function to work, and I think it's what Horshack expects, too.

Subject detection occurs whenever the camera can see a target subject, regardless of whether it can focus on it. The camera did this with earlier FW too - if you got closer than the lens's minimum focus distance, the camera still detected the subject even though it couldn't focus on it.

This new capability makes it so the camera doesn't have to work as hard to obtain focus, because you have artificially limited the near and far limits of focus. That makes sense to me.

If the camera continued to focus on a subject beyond the limits you set, what would be the point of setting focus limits?

PLShutterbug said:

lokatz said:

Horshack said:

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

Ouch. This almost renders it useless for me. I can only help that "appears" means you're not certain and there's a chance it still does limit the AF when using subject detection. I switch subject detection off at times, but in situations where I might use a limiter (hide shooting and similar), it remains very useful.

Click to expand...

I just experimented.

... Regardless of distance the camera still detected the face, and kept the focus box on the face, but it stopped attempting to focus at the limits.

This is exactly how I expect the function to work, and I think it's what Horshack expects, too.

Click to expand...

Thanks for testing this, but what you describe is the EXACT opposite of what @Horshack described. He said "the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range."

I can only hope you are correct.

lokatz said:

PLShutterbug said:

lokatz said:

Horshack said:

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

Ouch. This almost renders it useless for me. I can only help that "appears" means you're not certain and there's a chance it still does limit the AF when using subject detection. I switch subject detection off at times, but in situations where I might use a limiter (hide shooting and similar), it remains very useful.

Click to expand...

I just experimented.

... Regardless of distance the camera still detected the face, and kept the focus box on the face, but it stopped attempting to focus at the limits.

This is exactly how I expect the function to work, and I think it's what Horshack expects, too.

Click to expand...

Thanks for testing this, but what you describe is the EXACT opposite of what @Horshack described. He said "the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range."

I can only hope you are correct.

Click to expand...

Horshack is correct, but the fact the camera "identifies and select subjects" doesn't mean that the camera will be able to focus on them + it will only recognise the subject as long as it can be identified (not too blurry, then). If it can help, I gave details here :

https://www.dpreview.com/forums/post/68344412

Pierre Lagarde said:

lokatz said:

PLShutterbug said:

lokatz said:

Horshack said:

Practical benefit of focus limiter use

How using the Z8's focus limiter actually benefits you in terms of AF is something I've been spending considerable time on examining. For now it appears the camera does not integrate the focus limiter configuration into its subject detection or tracking algorithms, meaning the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range. This implies that the limiter will not help you in isolating or excluding subject detection/tracking based on distance.

Click to expand...

Ouch. This almost renders it useless for me. I can only help that "appears" means you're not certain and there's a chance it still does limit the AF when using subject detection. I switch subject detection off at times, but in situations where I might use a limiter (hide shooting and similar), it remains very useful.

Click to expand...

I just experimented.

... Regardless of distance the camera still detected the face, and kept the focus box on the face, but it stopped attempting to focus at the limits.

This is exactly how I expect the function to work, and I think it's what Horshack expects, too.

Click to expand...

Thanks for testing this, but what you describe is the EXACT opposite of what @Horshack described. He said "the camera identifies and selects subjects the same as it would with or without the limiter enabled, regardless of whether the subjects in the frame are within the configured limiter distance range."

I can only hope you are correct.

Click to expand...

Horshack is correct, but the fact the camera "identifies and select subjects" doesn't mean that the camera will be able to focus on them + it will only recognise the subject as long as it can be identified (not too blurry, then). If it can help, I gave details here :

https://www.dpreview.com/forums/post/68344412

Click to expand...

Ok, then I misinterpreted what @Horshack said. Thanks for clarifying!

Addressing the questions above, here's a short video I did showing the subject identification, selection, and tracking behavior with and without the subject inside a focus limiter range.

Horshack said:

Addressing the questions above, here's a short video I did showing the subject identification, selection, and tracking behavior with and without the subject inside a focus limiter range.

Click to expand...

Great subject for your eleven-thousand-and-oneth post!

Now I understand better not just how this works, but why tying the two together could be desirable. The challenge with tying them would be, how do you determine if a nearer subject is within the focus limiter range? I guess the answer is that the camera would hunt to the near limit, just like it hunts to the MFD now. It it can’t focus then it should give up and look for a matching subject further away.

Horshack said:

Addressing the questions above, here's a short video I did showing the subject identification, selection, and tracking behavior with and without the subject inside a focus limiter range.

Click to expand...

Though...from what I saw, active AF-C on the eye of the close subject didn't behave the same way with focus limiter on. Without focus limiter, it didn't want to let go until the eye completely left the frame. With focus limiter, it switched a bit earlier. Not sure how repeatable that is though, and one could wish it switched much earlier!

Trazan said:

Horshack said:

Addressing the questions above, here's a short video I did showing the subject identification, selection, and tracking behavior with and without the subject inside a focus limiter range.

Click to expand...

Though...from what I saw, active AF-C on the eye of the close subject didn't behave the same way with focus limiter on. Without focus limiter, it didn't want to let go until the eye completely left the frame. With focus limiter, it switched a bit earlier. Not sure how repeatable that is though, and one could wish it switched much earlier!

Click to expand...

With the limiter off It stays on the near mannequin until it leaves the screen on the first pan at 0:58 but then switches away much faster on subsequent pans, matching the behavior with the limiter on. However, I've done some new experiments in different light levels which do demonstrate the limiter having a benefit (switching subjects faster)...

In the new experiments I found that in lower light levels, the AF-C's variability in maintaining PD focus increases, which induces it to hunt and switch subjects faster, ie before the subject leaves the frame. In that lighting scenario the limiter doesn't show any benefit, which switches at about the same rate vs the limiter off. However, in good light levels, the AF-C's lower PD focus variability allows the subject lock to be maintained much longer, which causes it to hold onto the near mannequin until it leaves the frame (like it did initially at 0:58); by contrast, in that same good light level the limiter causes a switch to the far mannequin much earlier (due to focus variability caused by the limiter), demonstrating a clear benefit of the limiter. I'll post a video later tonight which demonstrates this.

In this video I demonstrate a novel use of the Z8 focus limiter: evaluating the amount of "stress" the AF is operating under for a given subject and lighting scenario. By stress I mean how much trouble the AF system is having establishing and maintaining a phase-detect lock on your subject. In extreme conditions the amount of stress is obvious because it manifests as hunting and seeking behavior. However there's a large gray area of scenarios where the AF system appears to be operating well but is actually having difficulty with your subject. This novel approach uses the limiter's configuration screen to reveal how much variability (aka stress) the AF system is experiencing.

Is this a limitation on the near/far distances from the camera a lens will track through while acquiring focus or a limitation on the near/far distances from focus lock the lens will search to maintain focus?

The latter would be of interest to me. For example If I'm photographing raptors, I may set a range of +/- 1 meter from focus lock. I'm assuming the camera will maintain lock while the bird moves in flight and will continuously adjust the distance estimate to that subject. While making adjustments to maintain focus lock, it wouldn't depart from an estimated distance by more than 50cm+/- from the focus distance at any given moment.

That sounds pretty good to me. I might set a wider range for a larger mammal or a herd, or a narrower range during a portrait shoot. In any event, if the limit is on how much closer or farther the camera will look when tracking and maintaining focus lockn on a subject, that sounds useful.

--
Bill Ferris Photography
Flagstaff, AZ

Steve just posted an excellent instructional video on the setup, use, and practical implications of the limiter. Will likely be the definitive video on the subject.

Tbh, this is so complicated I really can’t see myself bothering to use it.

jimdelves said:

Tbh, this is so complicated I really can’t see myself bothering to use it.

Click to expand...

Yeah, I was excited when I heard about the feature, but don't like how it was implemented. Feels too manual and something that can be automated/use AI recognition.

--
Ryan

Through trial and error I stumbled onto a method that appears to get the camera to reliably ignore subjects that are outside the focus limiter's range. Here's a short video describing the method:

Thanks for the great info!

I was happy to see that Steve Perry gave you credit as source for his new video on this subject.