Focal-Plane Shutter Anomaly

"Annika1980" wrote in message
...
Check out this frame from a video I made yesterday with the Fab 5D2.
No way that shaft is flexing that much.

http://www.pbase.com/bret/image/113518953/original

Oh the joys of video artifacts. There are a number of ways a camera
manufacturer can approach video capture and I don't know enough about your
camera to comment with authority but here's some principles which may shed
some light on it.

Firstly I guess the picture is a crop from a larger landscape frame, that is
to say the camera was held the normal way up and you've only shown us a bit
of it. If the camera was held 90 degrees rotated then what follows is
b*&^%&*x. I also guess you're in the USA and therefore your camera is
shooting at 30Hz progressive scan (and then maybe converting to 60Hz
interlaced for video display but that's not important).

In principle there are two techniques for frame capture on the CCD and its
subsequent transfer. You can capture the whole frame in one go and then
read it out line by line during the 1/30 second of the frame. This reduces
intra-frame movement artifacts but also reduces the time available in which
to capture light which has all sorts of other consequences.
Alternatively you can capture a line at a time and read it out as you go
along. This maximises light collection and thereby improves signal to noise
ratio, low light performance etc but gives rise to problems with movement
which occurs during the frame. My guess is that your camera uses this
technique.

What I suspect is happening is that the camera is capturing a line at a
time, starting at the top, and reading it out *while still capturing light
on subsequent lines*. By the time the next line is captured the stick has
moved forwards slightly so that it is now in a new position. And again for
the next line, etc.

As an experiment and for some fun try taking the same photo but holding the
camera rotated 90 then 180 degrees (ie. upside down). Upside down should
bend the stick the other way.

Hope that helps,
Calvin

"Annika1980" wrote in message
...
On Jun 9, 3:16 pm, "Calvin Sambrook" wrote:

As an experiment and for some fun try taking the same photo but holding
the
camera rotated 90 then 180 degrees (ie. upside down). Upside down should
bend the stick the other way.

That's exactly what I plan on doing, and some stills as well.


Ah, now stills work differently again and I'd be surprised if you saw the
same issues. As there's not the time pressure to get the data off the CCD
during the 1/30 second frame (or whatever depending on your video standard)
the camera is free to expose the whole CCD in one go then read out at a
relatively leisurely pace.
That and the write speed of your memory card are what limit your repeat shot
speed in multi-stills mode.