Sony Z90 4k Jittering/Strobing?

[Alan Grove]

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

[Christopher Young]

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:

24 FPS vs 30 FPS vs 60 FPS (comparison) - YouTube

[Alan Grove]

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

[Alan Grove]

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

[Christopher Young]

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/

[Alan Grove]

Thanks again Christopher, I think I understand most of your post reply. However, what I don't understand is why bother selling a 4K camera with only 25fps that is useless for panning? I am sorry if I sound a bit thick here but I don't quite get the reason for 4K on my z90 if I cannot shoot without the judder? Thanks

[Doug Jensen]

Alan, if you look at the 4K 25p video output from the Z90 on a proper video monitor you shouldn't see any judder. If you do, you are either: 1) Using the wrong shutter speed. 2) Not using a good monitor. 3) Your eyes are not accustomed to viewing progressive video. In my experience, a lot of people who are used to watching 60p, 60i, 50i, or 50p video have a hard time adjusting to progressive video at 24p, 25p, or 30p. In fact, that is why a lot of people have their home televisions set for "motion flow" scanning so everything looks like a soap opera.

I own a Z90 and I shoot nothing but 4K 24p and 30p video with it, just like all my other cameras (F55, FS7, FX6, Z280, S1H, etc.) I own. There is nothing different about the Z90 and I do not avoid camera movement, fast pans, or make any other compromises to compensate for progressive codecs.

My advice: Double-check your camera settings and view the output on a proper video monitor (not the LCD screen or viewfinder or computer monitor) that is set up to show progressive scanning correctly.

Doug Jensen’s Sony PXW-Z90, NX80, and AX700 Master Class - CHAPTER 1 FREE - YouTube

Sony PXW-Z90 Test Footage - YouTube

[Alan Grove]

Hi Doug, thanks so much for trying to help me with this issue. I have today received a call from a friend who has the Z90, and like me has never filmed using 4K with it. His 1st words to me were... (Hi Alan have you tried 4K with your Z90? I just tried and it looks shocking on the LCD and timeline?) I then told him I am trying to solve that very issue with my own Z90. I have tried lots of different shutter speeds Doug but nothing changes? I have it set at 25p 100mbs/60mbs with a shutter of 50. If I pan from left to right I just get a really bad judder as if the frame rate too low? I put it on my Premiere timeline and it plays back the same. However, if I change my sequence settings to push the framerate to 50fps it all looks fine? As for monitor, I have a TV/Monitor which handles both interlace and Progressive in 1080i and 1080p.
PS: Can you confirm Doug that when using the LCD or Eyepiece there is no judder when panning?
Thanks Doug for your advice

[Doug Jensen]

Hi Alan, if you want my honest opinion, I think you are just not used to working with 24p, 25p, or 30p video. Most professionals went through this "adjustment period" about 10-15 years ago when we stopped shooting interlaced video. Maybe you are a little late to the party? :-) Do you have "motion flow" or a similar setting turned on for your home TV?

In the early days, some professionals were so uncomfortable by the look of progressive that it was possible with one of my older cameras (F800 maybe??) to show a simulated 60p in the viewfinder while recording 30p internally. Personally, I didn't need it, but it helped some people make the transition. I haven't shot anything that wasn't 24p or 30p since 2006 and I cannot stand the look of any frame-rate faster than that. I am used to 24, 25, and 30 progressive and anything that looks faster immediately looks "wrong" to my eyes. And as proven by the "Hobbit" at 48 fps, most people agree.
https://gizmodo.com/the-hobbit-an-un...ps-fai-5969817

You and I are 180 degrees opposite on what we think looks correct. Neither one of us is wrong or right, it is just what each of us is used to seeing.

No, I do not see judder in my Z90's viewfinder or LCD. it looks exactly the same as 24p, 25p, and 30p looks on all of my cameras. YOU might call it judder -- but to me it looks perfectly normal. It doesn't look like interlaced and it doesn't look like 60p or 50p, so you are not used to it. I'm 100% sure your camera is functioning correctly and is perfectly capable of shooting 24p, 25p, and 30p 4K and HD video.

I suggest you shoot some 25p video. Bring it into Premiere and edit a short 25p video with transitions, a couple of graphics, etc. Then output it as a 25p file and upload it to Vimeo or Youtube. Then see if it doesn't look the same as everyone else's 25p video.