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URL: http://www.cely.com/test.html
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I received an e-mail warning from a couple
of fellow DSR 500 users, and decided to shoot my own tests to confirm the phenomenon
they described. (Don't you wish every shooter took the time to share this kind
of information!) Thanks, Dave and Steve!!! The camera was an NTSC Sony DSR 500WS.
The test was shot on DV-CAM stock in my workshop, and illuminated by 2 garden
variety 4ft fluorescent fixtures. The tubes were GE F40 Cool White Shop Lights
(slightly brighter than generic 4ft tubes). The power is typical of domestic US
current, 115VAC (nominal) at 60hz. My tests confirmed the color and exposure
shifts in both the electronic shutter and CLS (clear-scan) modes. I shot an interview and wanted
a shallow depth of field to throw the background into a soft focus. Under fluorescent
lights, I color balance and increased the shuttle speed to open the iris and the
picture began the above described situation. Please do the same and tell me what
you find. Have you every experienced this before and can you explain what might
be happening. I would like to know how many camera are affected by this as I'm
calling Sony next week." The following images are linked to Quicktime
Movie clips of my tests. The file sizes are rather large (about 1 meg each) so
they are best viewed with DSL or cable modem connections. I kept the length of these clips under
20 seconds, but they should be long enough for you to see the cyclic rate of the
color and exposure shifts. As expected, the shifts were constant - in keeping
with the phasing of the 60hz wall current powering the lights. When I shot a similar
test using a high frequency "flicker free" fluorescent ballast (similar
to a Kino Flo), there was no shift in color or exposure. Shutter Off: This is the "Control"
sample. Shutter 1/250th: The color
shifting is quite noticeable at this rate. Shutter 1/1000: It takes about
10 seconds to cycle from the normal color like the control to this green-shifted
& darker image. Shutter 1/2000: Here is a view
of the fluorescent tube in the fixture used to light the tests. As a result of a little thinking about
the issue, I believe that the matter is more of a lighting-related phenomenon
rather than a design flaw. Think about it... even film cameras cannot be used
in certain HMI, fluorescent and metal halide lighting conditions. The "flicker"
film cameras experience is purely shutter related. At 24 fps, and a select set
of other shutter speeds, the "spikes" emitted by AC arcs (which the above three
lighting sources really are) more or less sync to the camera and provide a consistent
exposure. When you change the film speed, sometimes the shutter will receive the
same number of spikes, sometimes not, resulting in exposure changes or "flicker".
In a video camera this is further complicated by the 3 different CCDS rather than
a single "gate". There is no reason this same effect
shouldn't apply to video cameras. I have a table of flicker-free "safe speeds"
for film cameras at http://www.cely.com/flickerfree.html
. As video cameras get more film-like, with 24fps progressive scan, etc., I wonder
if manufacturers will change the still-camera type electronic shutter speeds to
"frame rates" like film cameras use? Instead of 1/100th, 1/250th and so on, we'd
have 120fps, 240, 480, 960, 1200 and 2400fps settings for our shutters that would
permit flicker-free filming - uh, I mean shooting - under AC arc lights.
URL: http://www.cely.com/test.html
COLOR
& EXPOSURE
SHIFTS
WITH ELECTRONIC "SHUTTERS"
Here's the text of the
message:
"I'm a fellow
Sony DSR 500 user and came across a situation that has alot of
people scratching their heads in central California. Here is the
problem: The camera, like others, handles fluorescent lighting
fairly well after color balancing. But I have discovered that
with the shutter speed switched to 250, 500 or 1000th the color
shift begins rolling red and blue with the intensity increasing
the faster the shutter speed. Test this on a monitor a see the
image roll blue and red every 5-10 seconds. For the best results
iris down and point the lens directly at the fluorescent lighting.
(Also push the blue check button on your monitor and notice the
image turn bright and dark (or blue) at 5-10 second intervals.
The camera was white balanced on a white card in this position.
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