Most computer screens run at 60Hz and very often this rate can’t be changed. 25p shown on most computer screens requires 15 frames to be shown twice and 10 frames to be shown 3 times to create a total of 60 frames every second. This creates an uneven cadence and it’s not something you can control as the actual structure of the cadence depends on the video subsystem of the computer the end user is using.
There have been a number of threads in various forums about the way the images from the new Sony FS100 appear to judder or stutter when shooting at 25P or 24P. Most of the complaints appear to be coming from PAL areas where shooting 25P is common. This is not an issue unique to the FS100, in fact motion judder is often more noticeable with video cameras than film cameras even though the frame rates and shutter speeds may be exactly the same. Why is this?
One of the key issues here and I believe a very strong clue to what is going on is that most complain that the issue is most pronounced in areas of high contrast.
Our visual system picks up edges and other areas of high contrast to detect motion, in areas of high contrast any non-smoothness of the images motion will be more noticeable. The higher the resolution/contrast or more precisely the higher the MTF of the camera system the more we will notice judder and stutter. Just take fast motion in an Imax film as an example, it stutters like crazy.
The FS100 and similar high contrast/resolution cameras will appear to stutter at low frame rates more than a low contrast/low resolution camera. Edges in film are almost never instant changes from black to white, there is almost always some smoothing or dithering caused by the grain structure of film. So when you consider the FS100’s near complete lack of noise, which through it’s random nature will help mask judder and stutter and you have a worst case scenario. A camera with sharp edges and no noise.
Another strong contributing factor is the use of detail correction that adds a very definite, hard, non-motion blurred black or white edge around any areas of medium to high contrast, so unlike the very slightly dithered edges we would see in film we have instant light to dark or dark to light transitions occurring over a single pixel. In the case of a pan that hard edge is going to step uniformly from one position to the next, it won’t have any motion blur and it will increase edge contrast compounding the images judder as our visual system will notice these hard edges jumping from one place to the next.
The PMW-F3 although it uses the same sensor is less prone to this effect as it has a more sophisticated DSP and uses less detail correction and more aperture correction for image sharpening. Aperture correction blurs with motion as it is a type of high frequency boost and as you pan the camera the motion blur of the image reduces high frequencies so the amount of correction also drops thus helping smooth edges as you pan.
You also need to consider the results of watching 25fps video on a computer monitor typically running at 60hz. You will get judder as 25 does not go into 60 evenly, this helps explain why this “issue” is getting more airtime in Europe than in the US where 24P with pull up to 30P is common and of course 30P will display on a 60Hz monitor with no additional problems.
So in the case of the FS100 (or other cameras exhibiting this effect), I would suggest turning off the detail correction circuits or at the very least reducing the detail level if you are shooting high contrast images or anything with a lot of motion. It would also be interesting to compare similar pans at different speeds with some gain added to see if that helps.
I don’t think this is, as claimed by some, to be camera fault, more likely a result of a very clean, detail corrected image. Even an EX1 or EX3 will do similar things if your detail settings are too high. It’s not unique to the FS100, just one of those things that can happen when you have sharp pictures. When I watched the Sony F65 4k demo film “The Arrival” I noticed a similar increase in motion judder compared to film, again I put this down to high edge sharpness catching my eye and making me notice the cameras motion more acutely. Ohh that F65 stuff looked stunning!