Problems with Z6 ii / Z7 ii vignette control

[rgames1]

Having used Z6ii/Z7ii for timelapse for more than a year now, I keep running into issues with vignette correction in my timelapse sequences. The attached image is a good example - this is a composite of successive images of a sunrise shot, the later shot below the diagonal and the earlier one above the diagonal. It's hard to tell because the brightness changes are small but the lower half is brighter in the lighter mids / oranges but *darker* in the dark mids / blues. Obviously that's not what's actually going on in the blue portions - the camera is incorrectly recording the blues and/or incorrectly applying vignette correction. I saw this a few times on my Nikon DSLRs but very rarely - it happens all the time with the Z series. I have the same issue with two Z6iis and one Z7ii, so it's not a problem with this particular camera. I shoot in manual mode and adjust shutter speed as lighting changes for sunrise/sunset.

The result of this phenomenon is flickering corners in the timelapse video.

I've tried manually applying vignette correction and the image changes but the frame-to-frame differences remain. In other words, I can create a different look but the flickering remains. There's always a difference in the corners, usually when I adjust exposure (via shutter speed) between shots. It occurs most frequently with cloudless skies (or maybe it's just hard to see when there are clouds present).

Has anyone found a solution to this problem?

Thanks in advance.

 

[kenw]

Shooting RAW or JPEG? Exposure smoothing on or off? Active D-Lighting on or off? Time lapse video generation in camera or out of camera?

 

[WWeber]

How did you expose your pictures? Manual or automatic? If automatic then shutter or aperture priority or Program?

I would, if in automatic mode, use aperture priority, so the aperture is fix and gives the same vignetting in the complete series.

Maybe it could help to set the vignette correction to off

 

[rgames1]

Good questions - I am shooting raw with vignette control off, exposure smoothing off and D lighting off. I am shooting manual mode and manually adjusting shutter speed to adapt to changing light. Aperture and ISO are fixed through the entire sequence. I am not assembling the video in camera - I process the raw images in ACR and export from Lightroom. The photos above are what I see in ACR straight from the raw files.

As noted above, I can change the vignette settings in ACR and the images change but the differences in vignette remain. The effect is somehow baked into the raw file.

Also, the camera settings/procedure/postprocessing is exactly the same as I've been using for years with several Nikon DSLRs (D600, D610, D750, D800, D810, D850). I rarely saw this issue with DSLRs but see it all the time with three different Z series cameras. There's something about the way these raw images are processed that is different.

 

[skyrunr]

Have you tried NX Studio? Or viewing the RAW image in Photos? Can you post a link to the RAW image?

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[kenw]

Good questions - I am shooting raw with vignette control off, exposure smoothing off and D lighting off. I am shooting manual mode and manually adjusting shutter speed to adapt to changing light. Aperture and ISO are fixed through the entire sequence. I am not assembling the video in camera - I process the raw images in ACR and export from Lightroom. The photos above are what I see in ACR straight from the raw files.

As noted above, I can change the vignette settings in ACR and the images change but the differences in vignette remain. The effect is somehow baked into the raw file.

Also, the camera settings/procedure/postprocessing is exactly the same as I've been using for years with several Nikon DSLRs (D600, D610, D750, D800, D810, D850). I rarely saw this issue with DSLRs but see it all the time with three different Z series cameras. There's something about the way these raw images are processed that is different.

Thanks, that helps! Seems like you've got most things locked down and under control.

My suspicion is that the vignetting control is a bit of a distraction and what you are actually seeing here is aperture flicker. Or at least that may be a part of it.

Even though you are in manual mode with a fixed aperture the lens iris is moving for each exposure (different iris positions for liveview and exposure). In some lenses the iris does not consistently stop down to exactly the same position for each exposure. For stills this is no big deal, the exposure variation is quite low. For video the lens does stay stopped down continuously, so again no issue. But for timelapse where individual stills shots are put together into a video these small variations in iris position (and thus exposure) show up as flicker.

Now in theory depending on what aperture you are at this flicker would also slightly affect how the lens vignettes depending on how open the iris was for each exposure. So that might explain why you are seeing the center brighter but the edges darker in certain cases because of course you've got other things changing (the light level and your shutter speed). There are a lot of moving parts here when shooting a sunset in the field.

Aperture flicker is a well known problem with some lenses and time lapse. So I'd start there. If you've got an adapted manual lens you can use then that would keep the aperture fixed. The other option is to slightly dismount a native Z lens so the camera can no longer control its aperture. This isn't useful for practical photography, but it would be a way to establish if aperture flicker is likely the problem. You could potentially do this with a continuous light source (mid day shots, a computer monitor, etc) to keep things a bit more controlled for testing out what is the root cause.

Anyway, it might not be the entire puzzle, but given your shooting settings I suspect aperture flicker is at play.

 

[skyrunr]

Awesome and helpful post, I guess the no EXIF/lens data didn't help us any either.

 

[rgames1]

Good questions - I am shooting raw with vignette control off, exposure smoothing off and D lighting off. I am shooting manual mode and manually adjusting shutter speed to adapt to changing light. Aperture and ISO are fixed through the entire sequence. I am not assembling the video in camera - I process the raw images in ACR and export from Lightroom. The photos above are what I see in ACR straight from the raw files.

As noted above, I can change the vignette settings in ACR and the images change but the differences in vignette remain. The effect is somehow baked into the raw file.

Also, the camera settings/procedure/postprocessing is exactly the same as I've been using for years with several Nikon DSLRs (D600, D610, D750, D800, D810, D850). I rarely saw this issue with DSLRs but see it all the time with three different Z series cameras. There's something about the way these raw images are processed that is different.

Thanks, that helps! Seems like you've got most things locked down and under control.

My suspicion is that the vignetting control is a bit of a distraction and what you are actually seeing here is aperture flicker. Or at least that may be a part of it.

Even though you are in manual mode with a fixed aperture the lens iris is moving for each exposure (different iris positions for liveview and exposure). In some lenses the iris does not consistently stop down to exactly the same position for each exposure. For stills this is no big deal, the exposure variation is quite low. For video the lens does stay stopped down continuously, so again no issue. But for timelapse where individual stills shots are put together into a video these small variations in iris position (and thus exposure) show up as flicker.

Now in theory depending on what aperture you are at this flicker would also slightly affect how the lens vignettes depending on how open the iris was for each exposure. So that might explain why you are seeing the center brighter but the edges darker in certain cases because of course you've got other things changing (the light level and your shutter speed). There are a lot of moving parts here when shooting a sunset in the field.

Aperture flicker is a well known problem with some lenses and time lapse. So I'd start there. If you've got an adapted manual lens you can use then that would keep the aperture fixed. The other option is to slightly dismount a native Z lens so the camera can no longer control its aperture. This isn't useful for practical photography, but it would be a way to establish if aperture flicker is likely the problem. You could potentially do this with a continuous light source (mid day shots, a computer monitor, etc) to keep things a bit more controlled for testing out what is the root cause.

Anyway, it might not be the entire puzzle, but given your shooting settings I suspect aperture flicker is at play.

Yeah that's a good point. I always used to do the "lens twist" trick on DSLRs to prevent aperture flicker in timelapse but quit doing it on the Z series because I managed to convince myself that it's not an issue any longer. See this thread:

https://www.dpreview.com/forums/thread/4566875#forum-post-65025611

There were some comments in that thread that the aperture flicker issues were real on older lenses but basically non-existent on newer lenses. I somehow managed to convince myself of that but maybe I need to revisit whether that's the case.

As an aside, my z7 and z6 still do that (stupid) "aperture pulse" before every shot. If there were a way to prevent that then aperture flicker wouldn't be an issue. There is zero reason why you shouldn't be able to lock aperture when using manual focus, but you can't on z glass. But that's a discussion for another thread...

 

[rgames1]

Have you tried NX Studio? Or viewing the RAW image in Photos? Can you post a link to the RAW image?

I have not tried NX studio and I don't know what Photos is. I'll give NX studio a shot.

Here's a link to the images shown above, one is shot at one stop darker via shorter shutter time:

https://drive.google.com/drive/folders/1NRkRywJULhE25hTF2WEZnI5PTShfM-mI?usp=share_link

 

[skyrunr]

I think kenw nailed the cause.

Windows "Photos" is the built in image viewer that works with the NEF Codec you download from their website. You might be a mac user, but Apple has a built in photo viewer to, MyPhotos? MyGuess. MyLOL.

--
SkyRunR
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
TIPS: Be kind, RT#M, use gear not signature, limit/shorten replies with quotes!
'Open your eyes and look within.' Bob Marley