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Flickering?


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#1 Rominjoe

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Posted 16 April 2017 - 11:58 PM

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Can anyone tell me what is going on with this flickering going on with the leaves above my head? What's it called? How do I ensure it doesn't happen again?



#2 cws

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Posted 18 April 2017 - 12:19 AM

Hi.  It can help a lot if you can provide more information about the camera settings used to shoot the clip, but if you look carefully around the frame, including at the car and also the grass at bottom edge of frame, you'll notice they are also "flickering", although you mainly notice it in the leaves at top as that is where it is quite intense.

Looks like the camera is in autofocus mode... but I don't think that's a cause.

I'm thinking it's something to do with your exposure settings as it "almost" looks like a very fast exposure adjustment trying to compensate for the peak highlight of the sky just above your head ... what shutter speed, frame rate and ISO were you set at?  Were you using manual controls or some auto functions for exposure?


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#3 Rominjoe

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Posted 18 April 2017 - 01:15 AM

Hi. Thank you for your reply. I didn't read these out but in a previous recording in which the exact same problem occurred, I read off the settings of:

23.98 fps

1920 x 1080

PP 8

Shutter 1/800

F 4.0

Im fairly certain the ISO is 100. If it's higher it's not by much.

 

At the time I was attempting to to see if I could get the clouds and the subject. I wasn't concerned with the WB (obviously) but it was on Auto WB at the time.

 

It was recorded on autofocus because I've been testing that out to see how well it works with the face detection. When I recorded on manual focus, the flickering did not occur so it's possible that could be the cause. Other videographers i've followed have sworn by the face detection AF but if that's a side affect of AF, I wouldn't want to risk it. 



#4 cws

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Posted 18 April 2017 - 01:29 AM

I'm tipping your shutter speed is the main culprit here.

1/800th is a very closed down shutter.... normally for video at 24fps (23.98 or 23.976 to be precise) you'd be looking at a shutter of around 1/60th of a second or 1/50th of a second, closer to a 180deg shutter.

Because you want a wide-open f-stop (4.0) at 100 ISO, normal practice would be to use a ND filter to reduce exposure, rather than reducing shutter speed so much.
You are compensating for about 4 stops of overexposure by reducing shutter speed where that should remain more consistent and the light is adjusted by other means, try it again at say 1/50th sec shutter with ISO at 50 and a 0.9ND (that would be around 4 stops to compensate for the shutter speed change)...  or if you have a polariser or variable ND try using that instead to cut some of the light... but keep your shutter speed around 1/50th.

:)


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#5 Rominjoe

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Posted 18 April 2017 - 01:42 AM

I'll have to order an nd filter for that lens. In the meantime, I'll record it again at the prescribed shutter in the same place tomorrow (when I get some daylight) and test your hypothesis.

 

Again. Thanks for the help.  


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#6 cws

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Posted 18 April 2017 - 02:23 AM

what camera and lens are you using?

Reason I ask is I did a quick handheld test outside on an A7r2 with Canon 17-40mm and didn't notice any flicker under similar lighting to your shot using similar settings, as well as what I suggested with variable ND, although I didn't check if face-detection was on, and I don't have a PP8 on the A7R2 (not that I think the picture profile has any affect here).
I'll test it again on a tripod with face-detection active...  I'm thinking maybe its a combination of the focusing with the shutter speed...



#7 Rominjoe

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Posted 18 April 2017 - 05:31 AM

Im using the a7sii with the sony zeiss 16-35 f/4. I think the AF and high SS are working together to cause the flicker bc it wasn't occurring in manual focus.
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#8 Rominjoe

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Posted 20 April 2017 - 01:21 AM

Ok so I've tried this at 1/60th SS and 1/800th with the AF and in every clip it shows the same fluttering image.

I've also tried it in every different AF video combination from multi zone to wide to center to flexi zone.

At this point I'm starting to wonder if this is a defect.:huh:

 

It definitely appears to be an AF issue because there is no flickering in MF.



#9 cws

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Posted 20 April 2017 - 01:24 AM

Ok so I've tried this at 1/60th SS and 1/800th with the AF and in every clip it shows the same fluttering image.

I've also tried it in every different AF video combination from multi zone to wide to center to flexi zone.

At this point I'm starting to wonder if this is a defect.:huh:

 

It definitely appears to be an AF issue because there is no flickering in MF.

Do you have another lens you can test it with?



#10 Rominjoe

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Posted 20 April 2017 - 01:34 AM

I just tried it with a 55-210 and got the same defect.



#11 cws

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Posted 20 April 2017 - 01:44 AM

Sounds like you need to ask if someone else with an A7Sii can test and report whether they see the same problem....  :(

maybe create a new post with that specific info...

good luck

Chris


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#12 Rominjoe

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Posted 20 April 2017 - 01:57 AM

I appreciate you helping me trouble shoot this.

Thank you for your time.



#13 Rominjoe

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Posted 20 April 2017 - 02:12 AM

I found this with someone else who had the same issue. Again, with trees...

 



#14 cws

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Posted 20 April 2017 - 02:31 AM

Interesting... see by the comments it's also an A7sii




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