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Sony NXCAM NEX-FS700 CineAlta
4K EXMOR sensor with SDI, slow-motion recording.


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Old October 23rd, 2012, 04:56 AM   #1
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Very bad aliasing at 100fps and 200fps

When I'm shooting super slowmotion at 100fps and 200fps I have bad aliasing on a lot of the shots.

Anything with lines or detail will have some aliasing... I suspect the FS700 to have a less good vertical resolution in super slowmotion mode (100fps and 200fps) even if on paper it's only from 400fps that the resolution drops down.

I'm shooting with a Metabones adapter and Canon L lenses: (24mm 1.4, 50mm 1.2, 70-200mm 2.8 II) with a shutter speed of 215 at 100fps and 425 at 200fps.
Unfortunately I can't upload any of the footage yet but I will as soon as possible...

Is there any solution to take away this aliasing in the Picture Profile or postproduction?

Apart from this issue I absolutely love this camera :-)!

Many thanks,

Steven
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Old October 23rd, 2012, 11:02 AM   #2
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Re: Very bad aliasing at 100fps and 200fps

Hi Steven,

I can't answer your question, but am interested in why you love this camera. What camera is it replacing? Did you get it mostly for the slow-mo? How do you deal with the ergonomics? You got me curious.

Mark
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Old October 23rd, 2012, 03:27 PM   #3
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Re: Very bad aliasing at 100fps and 200fps

Hi Mark,

It's replacing my HVX200 and Canon 5D II.

What I love about the FS700:

- overall size of the camera
- ND Filters
- Slowmotion (100fps and 200fps)
- top handle
- Canon lenses with Metabones adapter
- all the little buttons on the side (zebra, histogram,...)
- screw holes everywhere
- rec button on the top
- LCD screen on the top
- cheap SD cards
- the fact that it's a real camera... not a DSLR
- audio inputs

What I don't like about the FS700:

- Sony picture look
- the peaking option to help you focus
- aliasing in 100fps and 200fps
- battery life when using Metabones adapter
- LCD hood always moving
- saved Picture Profiles erased if you format SD card
- when shooting slow motion, every time you playback a shot the camera goes back to non-slow motion mode
- 3 frames "out of sync" on my HDMI 7'' monitor

But even with all those defaults I love shooting with this camera!!

Steven
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Old October 26th, 2012, 12:37 PM   #4
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Re: Very bad aliasing at 100fps and 200fps

A couple of thoughts:

1) Have a small capacity (so you won't be tempted to shoot with it) SD card JUST FOR CAMERA SETUPS - you don't lose the Picture Profiles in the camera when you format a card, but of course you'll lose your saved setups on the card. Hence, having a little 2GB card specifically as your 'Setup' card (and backing that up).

2) Yes, there is aliasing on the slomo modes - not much, but enough to treat with caution. I'd dial out the detail on your PP, but it's not going to get rid of it - the camera is bypassing a lot of image processing to get Slomo. It's not a Phantom Flex.
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Old October 26th, 2012, 02:44 PM   #5
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Re: Very bad aliasing at 100fps and 200fps

Quote:
Originally Posted by Steven Blatter View Post
When I'm shooting super slowmotion at 100fps and 200fps I have bad aliasing on a lot of the shots.

Anything with lines or detail will have some aliasing... I suspect the FS700 to have a less good vertical resolution in super slowmotion mode (100fps and 200fps) even if on paper it's only from 400fps that the resolution drops down.
No, the resolution drops substantially for *ALL* slow motion modes with a capture frame rate of greater than 60fps, though it's certainly true that between 100-240fps it's not too noticeable on MOST normal pictures. One saving grace is that it tends to be monochromatic aliasing which makes it less noticeable than coloured. You can see what's going on if you look at the zone plates that Adam Wilt shot: ProVideo Coalition.com: Camera Log by Adam Wilt | Founder | Pro Cameras, HDV Camera, HD Camera, Sony, Panasonic, JVC, RED, Video Camera Reviews . Scroll to the bottom of the page.

For the 24fps mode, the performance is pretty good, and Adam says this is representative of 60fps shooting as well. Now look at the next chart (240fps, true for 120fps as well) and it's pretty easy to work out why you're seeing what you do. There are four sets of circles on the horizontal and vertical axes which show up the aliases, and the centres of the circles show twice the Nyquist frequency - twice the resolution where true resolution turns to aliasing. Twice Nyquist is 1080lpph, hence the limit to true resolution with the camera in this mode is 540lpph - and that is obviously the case horizontally and vertically.

The reason is that it can't read ALL the photosites on the chip faster than 60 times per second. So it reads fewer, more often. It's pretty certain that the basic read mechanism is similar to the Canon C300 - form an output pixel from a block of 2x2 photosites - but it's only reading every other block horizontally and vertically. Hence, it's skipping 3 out of every four blocks or photosites. Since the effective chip is 3840x2160, there's a total of 1920x1080 possible blocks - skip to only read 1 in 4 and you're left with 960x540 to be upscaled.

So, at 240fps, it's reading a quarter the photosites at four times the speed compared to 60fps - hence still exactly the same number of photosites per second in either mode.

As an aside, it's exactly this system of read that the AF100 has in normal speed - but from a chip with more photosites than 3840x2160. Enough more to give alias free resolution of about 650lpph rather than 540lpph, also with severe monochrome aliasing above the limit. It's easy enough to prove that. Compare the patterns on the second set of Adams charts (ProVideo Coalition.com: Camera Log by Adam Wilt | Founder | Pro Cameras, HDV Camera, HD Camera, Sony, Panasonic, JVC, RED, Video Camera Reviews second chart down for 240fps) with the same charts he did for the AF100 ( ProVideo Coalition.com: Camera Log by Adam Wilt | Founder | Pro Cameras, HDV Camera, HD Camera, Sony, Panasonic, JVC, RED, Video Camera Reviews )

Ignoring the contrast differences, the actual pattern is IDENTICAL in form between the AF100 in normal mode and the FS700 in 240fps mode - the only difference is a scaling one, the twice Nyquist nulls are nearer the chart centre for the AF100 than for the FS700. That's the 650v540 difference mentioned earlier.
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Is there any solution to take away this aliasing in the Picture Profile or postproduction?
Not really. What aliasing does is refect a frequency back around the Nyquist point, and that can be seen on the blocks to the side and bottom of Adams zone plates. Frequencies of around 1000lpph turn into a series of very coarse (and lower contrast) lines. Technically, "real" lines of 1000lpph are being represented as aliases of 80lpph. And once that's done, it's impossible to subsequently say whether the original detail was 1000 or 80 - very fine or very coarse. It's coarse lines as far as the image is concerned, end of story.
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Old October 26th, 2012, 03:28 PM   #6
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Re: Very bad aliasing at 100fps and 200fps

David, I always learn something from your posts. I'm sure I speak for many - but thank you for the time you take to explain these interesting technical details.
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Old October 28th, 2012, 07:09 PM   #7
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Re: Very bad aliasing at 100fps and 200fps

Thanks for the very kind words, Andy!

Just one other point from Stevens list of likes and dislikes about the FS700. He lists amongst the dislikes the " Sony picture look".

I suspect I know what he means by that, but it's probably better to refer to the "default Sony picture look".

About 10-20 years ago, the "look" of a camera in this price range was largely fixed by the manufacturer in the factory, and that included things like detail level, saturation of colours etc. Only in the very high end models could they be tweaked by the user to suit.

But that's all changed now, with the levels of adjustments in menus of current cameras. Out of the box camera A may indeed have a "Sony look" and camera B a "Panasonic look" etc, but if you know what you're doing with the menus it's normally quite possible to give camera A a "Panasonic look" and vice versa. Nowadays it's everything to do with lineup, far less who has made the camera.
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Old October 29th, 2012, 03:55 AM   #8
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Re: Very bad aliasing at 100fps and 200fps

Thanks David for your answers!

Great to have precise information about why there is some the aliasing. I was just very surprised when I came back to the edit suite and saw on all my wide shot (swiss vineyards shot from a boat) that there were lines "jumping" in the background. In other words I'm not sure I can use the shots in my film...

And you are right about the Sony look, I found some good looks via the picture profile (thanks to all the guys in forums posting their PP!) but it's just a shame that Sony cameras don't have an out-of-the-box setting that I like.
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Old December 6th, 2012, 03:37 PM   #9
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Re: Very bad aliasing at 100fps and 200fps

Unfortunatelly, I have exactly the same bad experience!
I would say VERY bad especially in panning super slow-mo shots. I am really not happy about that. It would be interesting if external uncompressed recording imroves that
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Old December 6th, 2012, 04:08 PM   #10
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Re: Very bad aliasing at 100fps and 200fps

Quote:
Unfortunatelly, I have exactly the same bad experience!
I would say VERY bad especially in panning super slow-mo shots. I am really not happy about that. It would be interesting if external uncompressed recording imroves that
No, it won't. As well explained earlier in this thread, aliasing is a result of the photosites, which are not a factor of your recording method.
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