Tuesday, August 6, 2013

So I found this camera on eBay...

A thousand FPS of goodness
A Redlake MotionXtra HG-SE, to be precise. This camera does 1280x1024 24-bit color at 500FPS, and doubles in framerate every time the vertical resolution is halved, up to 32000FPS at 1280x16. It records to 1.3GB of internal SDRAM, giving 2 seconds of record time. While this may seem low, 2 seconds of footage at 500FPS translates into nearly a minute at 24FPS, and most fast events don't take all that long to happen anyway.

I'm pretty sure (though not certain) that the camera uses a Photobit PB-MV13 as its image sensor (the same sensor is found in cameras such as the Weisscam HS-1) and was made by AOS. The camera is identical to the AOS VITCam, and in fact, Redlake Imaging Studio is a rebranded version of AOS Imaging Studio.

The first step was to find a reasonable control computer for the camera. Unfortunately, the drivers were never updated for Windows 7, which means the control machine has to be a dedicated Windows XP system. Furthermore, most ExpressCard/PCMCIA Firewire adapters don't have 12V power lines, which means the the camera needed to be tethered to an external adapter as well.
Fortunately, it turns out that Apple was obsessed with Firewire until recent years, so the first generation (2006) Macbooks have full-sized Firewire ports, complete with 12V power. Plus, they were x86 (Core/Core 2 Duo), so they run Windows XP quite nicely.

The trickiest part of using this camera is lighting. At 500FPS, the camera is constrained to shutter speeds of 1/500 or faster. Furthermore, the 2005-era CMOS sensor it uses doesn't have the greatest sensitivity, and there is no option to turn up the sensor gain.
Initial tests with room lighting proved to be a dismal failure. I switched to a 300W halogen bulb, which at least gave usable results:

Sadly, the sensor really wants high color-temperature (bluer) lighting, so there was no way to make the image look decent with a halogen.
Fortunately, the home hydroponics market has spawned a bunch of semi-legit electronic metal halide ballasts. These are functionally equivalent to what the film industry calls "HMI" lights, and are good for around 25000 lumens at a color temperature of 5000K.
In addition, the camera is natively a C-mount camera. Unfortunately, most C-mount lenses don't go above 16mm format, which means the edges of the image degrade in quality. The solution to this is to use SLR lenses and an adapter; I'm a Nikon guy, so I chose F-mount as my mount of choice. Nikon F also happens to have the most lenses out of any mount (since the mount has not changed since the early 60's!)
Because the camera uses a sensor with a diagonal of 20mm, and not a full-frame 35mm sensor, the crop factor is approximately 2. This means that a 50mm normal lens behaves like a 100mm telephoto, and a 24mm wide-angle behaves like a normal lens.
Putting the metal halide lighting, a 50mm f/1.8 Nikkor lens, and some Jello together gave the following video:

If you look closely at the video, you'll notice numerous color and motion artifacts. These are not actual camera artifacts, but rather a consequence of the shitty early-90's AVI codec Imaging Studio uses. The solution was to export the frames as uncompressed BMP's first, then use FFMPEG to convert the sequence of BMP's into a high-quality video.
At this point, I also discovered that by default, Imaging Studio does not apply gamma correction, leading to some washed-out looking images. Applying a gamma of 1.5 and turning up the contrast resulted in much prettier, contrastier videos:

This past weekend, we (oneTesla) was at MuseCon in Chicago. One of the featured shows was Masters of Lightning (Terry Blake and Jeff Larson, with a pair of 12KW DRSSTC's). The sparks from the big coils were just bright enough to show up decently on the camera.


1000FPS (quick 'n dirty export with pretty bad artifacting):

Jeff also brought his wire exploder, so we filmed that as well. Both videos at 1000FPS.

The exploding wire produces some interesting stills: