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Tracking focus with a GH4 in the NA-GH4

technique focus GH4

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#1 peterbkk

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Posted 04 April 2015 - 06:19 PM

Caveat: Maybe you all know about this technique and find this thread a bit "ho hum".  In which case, please ignore.  But, for me, it was an exciting breakthrough that improved my success rate shooting moving subjects.

 

Situation:

 

Panasonic GH4 in a Nauticam NA-GH4 housing with either the 7-14mm, 12-35mm (dome) or the PZ 14-42mm (flat port) shooting video of octopus, cuttlefish and squid in Lembeh.  I wanted to be able to shoot these critters "up close" and "on the move" but still keep them in sharp focus.

 

Problem:

 

I don't trust any auto-focus tracking system and have not had reliable success using it with the GH4 underwater, especially in murky conditions.  I prefer to use AFL/AEL to lock in focus and exposure for the whole clip.  With the camera set to AFS and a small centre focus point, I lock in the focus on the eye of the critter at the start of the clip.  But, then the critter starts to move.  How do I ensure that the critter's eye stays firmly in the narrow depth of field?  Obviously I need to move the camera with the subject, keeping the distance between the critter's eye and the lens at the same distance.  But that's quite difficult, especially checking the focus with the small monitor on the back of the GH4.

 

Solution 1 (attach a better monitor):

 

Use a large monitor that has built-in focus peaking like the Shogun.  But, Nauticam have not yet released the Shogun housing.  And I need to get the footage now.

 

Solution 2 (flip on the GH4's focus peaking): 

 

Unfortunately, the GH4's focus peaking only works when the camera is set to manual focus (Panasonic: could this be fixed in a firmware update, please).  The lens / port combinations that I'm using don't have manual focus.

 

But (and here is my big breakthrough), the NA-GH4 housing has a MF-AFC-AFS switch in a convenient location.  

 

Here's what worked: Before diving, turn on focus peaking in the camera's menu and save it to your favourite UW custom setting.  Underwater, set the MF-AFC-AFS switch to AFS and use the rear lever to set AFL to get a sharp lock on the subject's eye.  Flip the MF-AFC-AFS switch to MF.  The lens stays at the same focus distance as locked in.  But now the subject is also covered with focus peaking dots.  As the subject moves, move the camera with the subject, ensuring that the focus peaking dots continue to flicker all around the subject's eyes.  

 

If it's not moving too fast (e.g. an octopus walking), I was able to keep the subject firmly in the plane of focus (9 times out of 10)...

 

Regards

Peter


Edited by peterbkk, 04 April 2015 - 06:28 PM.


#2 Nick Hope

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Posted 04 April 2015 - 09:29 PM

Thanks Peter. Nice idea. I must try this. I have Fn5 set to operate peaking. What peaking colour and level do you use for this type of work?



#3 Nick Hope

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Posted 04 April 2015 - 11:07 PM

By the way I've also had little success shooting with auto-focus. Even if it looks like it's working well underwater, get the footage on the computer and you can see the nasty little shifts in focus while it hunts. I badly wish we could lock off focus during a shot.



#4 thetrickster

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Posted 04 April 2015 - 11:51 PM

Nice idea Peter,

 

I've got the AE-Lock set to AF-Set, so have the camera to MF. Before filming I press the AE-Lock button (so it focuses) on something 1m away (roughly) and with a aperture of f5.6 > f7.1 you have almost the whole scene in focus (going by the hyperfocal distance) from 1m onwards...


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#5 peterbkk

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Posted 05 April 2015 - 05:59 AM

By the way I've also had little success shooting with auto-focus. Even if it looks like it's working well underwater, get the footage on the computer and you can see the nasty little shifts in focus while it hunts. I badly wish we could lock off focus during a shot.

 

Hi Nick,

 

Yes, both the auto-focus and auto-exposure show the GH4's still photo heritage.  

 

I recently panned upwards with the camera set for AE.  Looked OK at the time.  But, on the computer, I could see small step changes in the exposure as the scene panned from dark to light.  Not smooth.  Had to do a little keyframing in FCPX to hide the steps.

 

Now I always use AFL and AEL before starting to shoot.

 

Regards

Peter



#6 peterbkk

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Posted 05 April 2015 - 06:13 AM

What peaking colour and level do you use for this type of work?

 

I have the level set to "low" and the colour set to "white".

 

It might be overkill.   This setting makes the in-focus subject look like it's covered in sparkling snow.  Very pretty!  :)

 

If I was using it all the time, I'd definitely tone it down.  But, I am only using this technique for close-up subjects that will move.  Keeping them in focus is the most critical success factor for the shot so I am happy to have bright sparkling snow covering the subject and on the ground around the subject.

 

I found that, with an octopus or cuttlefish on the dark Lembeh sand, not only could I see that the subject's eyes were in the middle of the focus-peaking "snow" zone, but I could see a path of snow along which the animal could move and stay in focus.

 

Regards

Peter



#7 Nick Hope

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Posted 05 April 2015 - 09:07 PM

Now I always use AFL and AEL before starting to shoot.

 

Does that mean you're shooting in an auto exposure mode? If so, how are you running that? I've been shooting in manual, keeping shutter at 180 degrees and ISO at 200 as much as possible, and mostly using the eyeballs and the little exposure graph (bottom-centre) to judge exposure.



#8 peterbkk

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Posted 06 April 2015 - 12:40 AM

 

Does that mean you're shooting in an auto exposure mode? If so, how are you running that? I've been shooting in manual, keeping shutter at 180 degrees and ISO at 200 as much as possible, and mostly using the eyeballs and the little exposure graph (bottom-centre) to judge exposure.

 

 

Hi Nick,

 

I love the 3 Custom Settings feature (well, 5 actually but I use 3-2 and 3-3 for two rarely-used, 1080P, slow-motion settings) and I love the way the Nauticam housing let's you change between the Custom Settings quickly.   At the very least it's a quick way to get all the settings back to a known position if you've made a lot of changes.

 

I have identical base settings in all Custom Settings - things like shooting mode, colour profile, display preferences, my 4 WB presets, ISO=200, etc.  Then I have C1 set to Manual Exposure, C2 set to Shutter Priority (1/50s) and C3-1 set to Auto Everything.

 

I find myself using C2 most of the time, shutter fixed at 1/50s and letting the camera select the aperture.  I watch the histogram to see if it matches what I want. It is usually right.  I find the +/- button easy to access if I want to move the histogram left or right. Then, at the start of the shot (or a sequence of shots with similar conditions), I push the AFL/AEL lever to lock in both the focus and the exposure.  

 

C1 is for when C2 won't work (not very often).

 

C3-1 is for when I have been fiddling with all the controls, and a hammerhead swings by and my poor little brain is too excited to figure out how to set the camera.  It's the only setting where I have Auto-ISO (although I wish that I could set an upper limit for Auto-ISO in video mode - are you listening, Panasonic).

 

Regards

Peter


Edited by peterbkk, 06 April 2015 - 12:44 AM.


#9 thetrickster

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Posted 06 April 2015 - 02:43 AM

 It's the only setting where I have Auto-ISO (although I wish that I could set an upper limit for Auto-ISO in video mode - are you listening, Panasonic).


I agree. The main missing points for me are similar

1. AutoISO in 'M' Movie Mode
2. Upper limit of AutoISO

And having access to exposure compensation also, so we can ETTR a little bit.


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#10 peterbkk

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Posted 06 April 2015 - 03:38 AM

I agree. The main missing points for me are similar

1. AutoISO in 'M' Movie Mode
2. Upper limit of AutoISO

And having access to exposure compensation also, so we can ETTR a little bit.


Sent from my iPhone using Tapatalk

 

And, regardless of whether shooting M, P, S or A mode, display both shutter speed and aperture in the monitor, regardless of whether it is selected by the user or the camera.



#11 escape

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Posted 06 April 2015 - 04:19 AM

Just wondering why not use AF/AE Lock button (lever on the housing) as a AF (you can set that in the menu).

Then you don't need to switch back and forth the focus switch.

My focus switch stay at MF position always and I just press AF/AE lock button if I need AF (and peaking is working).



#12 thetrickster

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Posted 06 April 2015 - 05:22 AM

I looked at that but the AF/AE button doesn't operate if you are recording, but yeah good idea if not recording.


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#13 peterbkk

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Posted 06 April 2015 - 05:47 AM

Just wondering why not use AF/AE Lock button (lever on the housing) as a AF (you can set that in the menu).
Then you don't need to switch back and forth the focus switch.
My focus switch stay at MF position always and I just press AF/AE lock button if I need AF (and peaking is working).


Only one reason: I have never tried that option. :)

Do you allocate a function button to toggling focus-peaking? Because I wouldn't want it on all the time. Only when focus is tricky; close-up of moving critters.

I'll give that a try and see if it works better for me.

Regards
Peter

#14 escape

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Posted 06 April 2015 - 06:01 AM

Only one reason: I have never tried that option. :)

Do you allocate a function button to toggling focus-peaking? Because I wouldn't want it on all the time. Only when focus is tricky; close-up of moving critters.

I'll give that a try and see if it works better for me.

Regards
Peter

Yup. Fn1 is my focus peaking toggle. :)

#15 Nick Hope

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Posted 07 April 2015 - 12:19 AM

I agree. The main missing points for me are similar

1. AutoISO in 'M' Movie Mode
2. Upper limit of AutoISO

And having access to exposure compensation also, so we can ETTR a little bit.

 

Agreed (but I don't know what ETTR means).

 

 

And, regardless of whether shooting M, P, S or A mode, display both shutter speed and aperture in the monitor, regardless of whether it is selected by the user or the camera.

 

YES! This stops me from using the modes other than M because I want to know what the camera is doing.

 

Just wondering why not use AF/AE Lock button (lever on the housing) as a AF (you can set that in the menu).

Then you don't need to switch back and forth the focus switch.

My focus switch stay at MF position always and I just press AF/AE lock button if I need AF (and peaking is working).

 

I started operating that way (i.e. Manual focus and using the AF/AE lock button to lock it off with a one-off autofocus) but the minimum size of the focus area (the yellow rectangle) is quite large. With the lenses I've been using most (Oly 60mm macro and Oly 12-50mm) I've been having more success operating in AFS mode and using the AF/AE lock button to lock it. In that case the 1-area focus box can be a really small square.

 

Still, with those 2 lenses, the focusing options really suck. No manual focus on the 12-50 and IMO unusably fine focus gearing on the 60mm.

 

I think I'll be switching between AFS and manual focus a lot more in future.



#16 thetrickster

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Posted 07 April 2015 - 12:51 AM

 

Agreed (but I don't know what ETTR means).

 

 

'Expose To The Right'

(so you retain the highlights, as you can recover the shadows more, than if you blow the highlights...)

But this is only good with low ISOs and I try to only do this by 1/3 of a stop.

 

I've badgered Panasonic via twitter and email support with the AutoISO and display issues - also the this one:

* Display the histogram / exposure meter while you're changing ISO 

 

I keep hearing that the next firmware upgrade will be 'big' and will be announced in time for NAB2015 (so next week perhaps) - but no doubt it will be more aimed at the pro market, so all these useful functional improvements will be ignored no doubt!!


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#17 Pajjpen

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Posted 18 March 2017 - 12:12 AM

Old thread but I'm new to mft cameras (coming from using a GoPro the gh4 is a big step up for me haha)
My issue is with videoing moving subjects, with afs I need to keep the same distance to my subject as I was when I first focused before the shot (almost impossible)
When the switch is set to AFC it doesn't seem to be any difference at all, I can focus before a shot just like with afs but then that focus is locked at that distance, unless I hold down the af/ael button (my focus button) before the shoot and then press the shutter with af/ael button held down but it just means the camera is endlessly hunting and serves no purpose.
Any suggestions on what I'm doing wrong? Any input is appreciated!

#18 kc_moses

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Posted 20 March 2017 - 05:40 AM

Have a read at this:

 

https://www.dpreview...s/post/53919696

 

The paragraph that may apply to you is:

"If you need to use AF while shooting video, the best method is to turn Continuous AF off (this is important) in the menu, set the camera for AF and touch the screen whenever you want to refocus. Half-press shutter also works in this mode while shooting."

 

I shoot with Panasonic LX100 and this work, I use "back button focus" before recording, then start recording, if the subject moved, I can press (and hold) the shutter button halfway to refocus, sort of create a slow focus pulling. This work for fairly slow subject. For fast moving subject, I think AFC with Continuous AF on is better as long as you are close enough and the water is relative clear to have good contrast between your subject and other stuffs in the water.



#19 Pajjpen

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Posted 30 March 2017 - 10:25 AM

Thanks, I'll give it a try, gonna take some trial and error before I figure out when and where I can use C-AF but I guess it's the way to go until tracking becomes a viable option somewhere down the line.. Haha