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Sony 4K Ultra HD Handhelds
Pro and consumer versions including PXW-Z150, PXW-Z100, PXW-X70 / FDR-AX100

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Old July 19th, 2021, 03:18 AM   #1
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Sony Z90 4k Jittering/Strobing?

Hi, I have the Z90 and must be honest its a fab camera. Most of the time my projects have all been 1080 and in the LCD everything looks smooth as it should. However, when I switch to 4K mode the LCD does not show smooth movement? This is also the same when viewing though eyepiece? When panning fast or slow It looks as though it is strobing? As if it cant keep up with the resolution? Is this normal?
I would be grateful for any help please? thanks
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Old July 19th, 2021, 07:57 AM   #2
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Re: Sony Z90 4k Jittering/Strobing?

If you are shooting HD on the Z90 then most likely you are shooting at 50p. The Z90 in UHD (TV 4K mode) is only capable of shooting at 25p. The difference in motion cadence and temporal and spatial movement between 50 frames a second and 25 fps is enormous. You only have half the images per second, hence the strobing look. Basically, if you want to get a smooth pan at 25 fps you would need to pan at at least 50% of the speed that you would be panning at 50 fps. Even then it is not going to look the same. The old rule of thumb for shooting 35mm film at 24 frames per second when using a 35mm lens (a standard lens for 35mm film) for indoor drama was that a pan of a room would need to take around seven seconds to get an object on one edge of the screen to the opposite edge.

Probably to really see the difference is to look at this little example. This illustrates the difference between 24/30 and 60 fps. The same motion movements seen here are basically the same when comparing 25 and 50 fps. In other words 25p vs 50p:

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Old July 19th, 2021, 10:54 AM   #3
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Re: Sony Z90 4k Jittering/Strobing?

Hi Christopher, that is a great help. I actually shoot in 1080i 25fps 50 shutter, but this was my 1st attempt at 4K and was quite surprised to see this happening. I suppose I should just keep 4K for still video shoots until I can afford 4K 50/60fps.

Thanks again
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Old July 19th, 2021, 01:25 PM   #4
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Re: Sony Z90 4k Jittering/Strobing?

Hi Christopher, that is a great help. I actually shoot in 1080i 25fps 50 shutter, but this was my 1st attempt at 4K and was quite surprised to see this happening. I suppose I should just keep 4K for still video shoots until I can afford 4K 50/60fps.

Thanks again
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Old July 19th, 2021, 07:17 PM   #5
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Re: Sony Z90 4k Jittering/Strobing?

Shooting 50i is 25 frames per second but they have now been split into fields, half frames of odd and even lines. You effectively have 50 images refreshed across the screen per second. It's a bit more involved than my following explanation as the complex physiology of the human eye is involved. Basically the persistence of human vision is about one twentieth of a second. So an imagef flash of 1/25 duration is starting to die in the viewers eye before the next 1/25 image is flashed to the eye. Flashing images at every 1/50 of a second means the image is refreshed in the eye well before the the previous image has died. Basically 50i exhibits the same motion characteristics as 50p but at half the vertical resolution of 50p. Same goes for 60i vs 60p.

The reason 50i and 60i exist is that in the early days of television 25 and 30 frame transmission flickered very badly. It was then decided to use the properties of AC power system to transmit the TV signal images. The first field of the 50/60i image is transmitted on the first phase of the of the alternating current followed by the second field of the image on the second phase of the AC power. That way the 25/30 images were broadcast as 50/60 images making movement look much smoother.

Bare in mind the shutter speed used in conjunction with the frame rate used will also have an impact on perceived motion smoothness. If I have to work with already shot 25p footage in a 50p edit I often use Re:Vision Effects RSMB (Real Smart Motion Blur) to overcome the jerkier motion of the lower frame rate footage. Have a look at examples #2 and #3 at the RSMB page below. #3 "The Fighter" example is a good demonstration of how 24p footage can look quite smooth with the correct amount of inter-frame blur and blending.

Chris Young

https://revisionfx.com/products/rsmb/
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