Funny Zoom

[samdring]

What happened here? Messing around at home - appear to have zoomed and shifted but the snowmen show little movement?
10D with 28-135 on IS


http://www.bytephoto.com/photopost/data/500/1234IMG_0627_edited-med.JPG?2360

[agit-prop]

Looks like about a 2 second exposure where you pressed the shutter, held the camera fairly still for one second and then moved the camera. The first second was enough to capture the snowmen. During the 2nd second, the camera captured the trail of video frames from the TV. The snowmen didn't leave trails (actually they did but they're very dim) because they're not very well lit.

[samdring]

Thanks - think I understand that so far but why the multiple 'shots' of the screen?

[teddynet]

Screen flicker?

[RichardtheSane]

THere is about 25 frames there, so if you have a standard 50-60hz screen that is about half a second of movement, a quarter of a second if you have a 100hz tv.
Each frame represents a single screen refresh on your tv.

[agit-prop]

While the tv operates at 50 or 60 Hz (50 Hz in UK) there are only 25 frames per second. The blanking interval occurs every frame, not evey field. Therefore each frame in that shot is one 25th of a second

[samdring]

Wow - thank you both.
It won't have escaped attention that the shot was of 'Discovery Channel'

[agit-prop]

So, was it a 2 second exposure?

[PacAce]

Agit-Prop wrote:
While the tv operates at 50 or 60 Hz (50 Hz in UK) there are only 25 frames per second. The blanking interval occurs every frame, not evey field. Therefore each frame in that shot is one 25th of a second

It's been a while since I took a TV course in college (electronics eng'g) but I'm pretty sure the screen DOES blank out after every frame. Otherwise you'd see the retrace scan line as the gun went from the bottom of the screen to the top for the 2nd field of the interlaced frame. In other words, the frames may be shown at 25 frames per second but the fields are shown at 50 per second (or 30 and 60 respectively for the US).

[agit-prop]

You are correct!

I stand corrected

[samdring]

Agit-Prop wrote:
So, was it a 2 second exposure?
1 sec @ 3.5 28mm but I suppose the principle of the explanation still holds?