Z8 Video AF...What am I doing wrong?

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Steve Miller

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Hi,

After successfully shooting still images of hummingbirds at a local park, I tried shooting some video. My setup is a Z8 and 400/4.5 lens. I use back button focus, was shooting in AF-C with bird subject detection and primarily switched between wide-L and a custom box that is slightly larger than the wide-L box. The hummingbirds were approximately 12 to 30 feet from me (the 400/4.5's MFD is 8.2 ft). When I was shooting stills with this exact setup and settings, I never had a problem focusing. The lens would easily go from the closer birds at 12 ft to the farther away birds at 30 ft.

However, when I was shooting in video mode, it took FOREVER to obtain focus if I was first shooting at 30 ft away then switched to the closer birds at 12 ft. The same happened when I tried to switch from focusing at 12 ft to focusing at 30 ft. It basically made it useless (with such fast moving birds) to switch distances. Note: since I needed to shoot at 12 ft and the focus limiter on the lens is at 5m, I had the switch set to FULL to ensure I could focus closely.

FYI, my video settings were 3840x2160 at 120 fps (I want to get slow-mo footage of the hummers, thus the high frame rate), H.265 8-bit (MOV), and exposure settings of 1/250 (closest I could get to doubling the frame rate) and f/4.5 (with Auto ISO).

I assume this is user error and I have some video AF setting not setup correctly. Any thoughts as to what I'm doing wrong?

Thanks,

Steve

P.S. Here's a still shot from the setup described above. Though this is only a single image at the closer distance, I'm definitely not having this focus hunting issue when switching from near to far subjects shooting stills.
SJM-20240809-Z8-0650-Topaz-2.jpg
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Steve Miller said:
Hi,

After successfully shooting still images of hummingbirds at a local park, I tried shooting some video. My setup is a Z8 and 400/4.5 lens. I use back button focus, was shooting in AF-C with bird subject detection and primarily switched between wide-L and a custom box that is slightly larger than the wide-L box. The hummingbirds were approximately 12 to 30 feet from me (the 400/4.5's MFD is 8.2 ft). When I was shooting stills with this exact setup and settings, I never had a problem focusing. The lens would easily go from the closer birds at 12 ft to the farther away birds at 30 ft.

However, when I was shooting in video mode, it took FOREVER to obtain focus if I was first shooting at 30 ft away then switched to the closer birds at 12 ft. The same happened when I tried to switch from focusing at 12 ft to focusing at 30 ft. It basically made it useless (with such fast moving birds) to switch distances. Note: since I needed to shoot at 12 ft and the focus limiter on the lens is at 5m, I had the switch set to FULL to ensure I could focus closely.

FYI, my video settings were 3840x2160 at 120 fps (I want to get slow-mo footage of the hummers, thus the high frame rate), H.265 8-bit (MOV), and exposure settings of 1/250 (closest I could get to doubling the frame rate) and f/4.5 (with Auto ISO).

I assume this is user error and I have some video AF setting not setup correctly. Any thoughts as to what I'm doing wrong?

Thanks,

Steve

P.S. Here's a still shot from the setup described above. Though this is only a single image at the closer distance, I'm definitely not having this focus hunting issue when switching from near to far subjects shooting stills.View attachment 95259
Click to expand...
The camera is incapable. Might work at 24fps, but I doubt it. Best option is to manually rack focus. It's asking for a lot, I am actually not sure there is a camera capable of doing this.
 
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Thanks.

Well...I guess I feel better that I wasn't doing something wrong?! So the issue is it's too difficult for the camera to quickly obtain focus when the processor is trying to shoot 120 fps. In other words, an overload for the processor and the AF system?

Steve
 
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Got it.

If my goal is slow-mo video of a hummingbird, is there any way to do it with the Z8, assuming I need to shoot at something like 60 fps so as to not overload the camera's AF and sensor processing capabilities?
 
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There is a setting in the video custom controls section (not sure which specific setting on a z8 since that's in the basement, but on the z9 it is "g6") that sets the AF focus speed - it goes from a range of -5 to +5 where +5 is the fastest and -5 is the slowest. If I remember correctly, it is set to 0 as a default which is fairly slow - I believe this is for the artistic slow motion focus effect that you often see. When set to 0, it focuses from 15' to 150' in about 7 seconds on a 400/2.8 TC, but less than a second when set to +5.
 
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Also, I was able to get some footage yesterday at 120 fps, though I had to be pre-focused near the flower where the hummingbird ended up feeding. I guess I can just use my current setup but use manual focus override to at least get the lens close to where the AF system is going to be looking for the subject. I'll give it a try.
 
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dupcak said:
There is a setting in the video custom controls section (not sure which specific setting on a z8 since that's in the basement, but on the z9 it is "g6") that sets the AF focus speed - it goes from a range of -5 to +5 where +5 is the fastest and -5 is the slowest. If I remember correctly, it is set to 0 as a default which is fairly slow - I believe this is for the artistic slow motion focus effect that you often see. When set to 0, it focuses from 15' to 150' in about 7 seconds on a 400/2.8 TC, but less than a second when set to +5.
Click to expand...
Thanks! I'll give it a try.
 
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Steve Miller said:
Got it.

If my goal is slow-mo video of a hummingbird, is there any way to do it with the Z8, assuming I need to shoot at something like 60 fps so as to not overload the camera's AF and sensor processing capabilities?
Click to expand...
You can do it at 120, just don't expect to rack focus using AF very fast and far. Focus on a target flower, leave it there, not wide open to give you some leeway of DOF, let it roll, and you have a good chance of getting a few seconds of usable footage. Also, I would move up the bitrate and get off the Auto ISO. Use an ND to get you the 180 shutter angle.
 
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Nimi said:
The camera is incapable. Might work at 24fps, but I doubt it. Best option is to manually rack focus. It's asking for a lot, I am actually not sure there is a camera capable of doing this.
Click to expand...
Why would the performance be any different for video and still photography from the same camera? I can buy that AF is new to the video industry, but if I can, for instance, hold shoot stills in AF-C at 20 or 30 fps such that when I scroll through the images after I get what amounts to a full motion video with the focus following everything the whole time, what prevents the very same camera from recording that same scene as video with the AF behaving in the same way?
 
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SCoombs said:
Why would the performance be any different for video and still photography from the same camera? I can buy that AF is new to the video industry, but if I can, for instance, hold shoot stills in AF-C at 20 or 30 fps such that when I scroll through the images after I get what amounts to a full motion video with the focus following everything the whole time, what prevents the very same camera from recording that same scene as video with the AF behaving in the same way?
Click to expand...

Because the processor is also working full time on the inter-frame compression. That's why it overheats in video, not in stills.

And I'm not sure it will actually AF AND rack on a target that size, moving this fast and that far even in stills mode.
 
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Nimi said:
You can do it at 120, just don't expect to rack focus using AF very fast and far. Focus on a target flower, leave it there, not wide open to give you some leeway of DOF, let it roll, and you have a good chance of getting a few seconds of usable footage. Also, I would move up the bitrate and get off the Auto ISO. Use an ND to get you the 180 shutter angle.
Click to expand...
Thanks!
 
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Have you checked your AF Lock On settings. For video, people normally prefer a slow transition from a near focus subject to an alternate background subject. That makes it much harder to quickly focus on a fast moving subject like a hummingbird. Adjust the setting to the fastest possible option and see if that helps. If there is a specific feeder or flower near the right distance, you might customize a button or ring to help you move to that distance and position more quickly. Most of your settings are not carried over from stills to video so you need to take the time to review all settings and make changes.
 
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There are two settings in the Custom Settings Menu that affect focus tracking when shooting Video...these are G6 and G7. G6 controls how fast the AF will rack when the system detects what it was tracking is out of focus. G7 adjust how quickly the AF system will try to re-aquire focus once focus is lost on what was being focused on or tracked.

With G6, if you pan to something else to focus on, a bird, a flower, person, or whatever, this setting determines the focus speed the system will use to lock in the new focus point. With video, there are times you want to change in focus to happen smoothly and times you want it to snap right into focus. This does not have any impact on how quickly the system will identify something to focus on. With G7, it's similar to still photography when something passes between the camera and the subject you're focused on or tracking and you don't want the camera to immediately switch to whatever blocked the subject. G7 allows you to adjust the time delay before the camera attempts to look for another subject.

Look at and adjust these settings to see if that might help. Pages 673 & 674 of the Z8 Reference Guide.
 
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The Z8 will video AF on hummingbirds in AF-C but the bird needs to be relatively LARGE in the frame -- much larger than it would be with the 400mm at 30 feet. You can compensate somewhat using single point AF, which is fine if the bird isn't moving(!). As Nimi indicated, video AF is much more limited compared to stills. All hybrids from all manufactures suffer from this problem.
 
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Steve Miller said:
Hi,

After successfully shooting still images of hummingbirds at a local park, I tried shooting some video. My setup is a Z8 and 400/4.5 lens. I use back button focus, was shooting in AF-C with bird subject detection and primarily switched between wide-L and a custom box that is slightly larger than the wide-L box. The hummingbirds were approximately 12 to 30 feet from me (the 400/4.5's MFD is 8.2 ft). When I was shooting stills with this exact setup and settings, I never had a problem focusing. The lens would easily go from the closer birds at 12 ft to the farther away birds at 30 ft.

However, when I was shooting in video mode, it took FOREVER to obtain focus if I was first shooting at 30 ft away then switched to the closer birds at 12 ft. The same happened when I tried to switch from focusing at 12 ft to focusing at 30 ft. It basically made it useless (with such fast moving birds) to switch distances. Note: since I needed to shoot at 12 ft and the focus limiter on the lens is at 5m, I had the switch set to FULL to ensure I could focus closely.

FYI, my video settings were 3840x2160 at 120 fps (I want to get slow-mo footage of the hummers, thus the high frame rate), H.265 8-bit (MOV), and exposure settings of 1/250 (closest I could get to doubling the frame rate) and f/4.5 (with Auto ISO).

I assume this is user error and I have some video AF setting not setup correctly. Any thoughts as to what I'm doing wrong?

Thanks,

Steve

P.S. Here's a still shot from the setup described above. Though this is only a single image at the closer distance, I'm definitely not having this focus hunting issue when switching from near to far subjects shooting stills.
Click to expand...
Your still is super sharp! I do video with the Z8 and 400mm lens, seems to be "okay", though maybe I have lower standards? These are some examples,
https://flic.kr/p/2q79nPq
 
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