Adam Wilt and I presented a talk about the new Sony FS700 camera to an audience at CineGear 2012. As part of our preparation we ran around and shot a bunch of slow motion night footage… which is certainly something I've never been able to do before.
That was a VERY informative experience because we found a very interesting "gotcha" when shooting 240fps on city streets…
It's been pointed out to me that my original article had things slightly wrong. I've since made some revisions. 6/9/12
The FS700 is similar to the Phantom in how it operates. When shooting slow motion the camera records first to a buffer, and when the buffer is full it lays the footage off to an SD card for storage. The reason for this is fairly simple: it's impossible to cram 240fps footage onto an SD card fast enough. The throughput just isn't there. The buffer is solid state memory, which is volatile but also very fast. It's a perfect, albeit temporary, capture storage area.
When buffering is finished the camera writes the buffered data to the SD card at 60fps, the fastest write speed the card will support. It's good that the data is laid off as fast as the camera can manage because that gets us up and shooting again as fast as possible. It's also bad, but for a reason I never suspected.
Take a look at this Quicktime movie, assembled from one 240fps night shot: