Difference between panning and Dollying with Ex1?

[BobDiaz]

matthew77,

I guess I should have pointed out that the "rolling shutter" isn't a mechanical shutter, but an electronic simulation of a mechanical shutter. While nothing is moving, it's a bit easier to picture a mechanical shutter moving, to try and understand what is going on.


To everyone,

When the shutter speed is set to 1/48 of a second (20.8 ms) for 24p, the top row is set to gather light (the shutter opens), and the command to gather light is moved down row by row until it reaches the last row in 1/60 of a second (16.7 ms).

There is a delay of 4.1 ms (0.25/60 of a second) where all the pixels are gathering light at the same time. Then starting at the top row and moving down, the pixels are read row by row (the shutter closes). This takes 1/60 of a second (16.7 ms) to read all the rows.


Research by Eric Pascarelli, shows that the "rolling shutter" takes 1/60 of a second to move through the CMOS sensor. See;

http://www.dvinfo.net/conf/showthread.php?t=112362

Eric provided the key that enabled me to calculate the impact of the "rolling shutter" when panning quickly. For example: If a pan takes xxx seconds to move from one side of the display to the other the skew is yyy (see below).

1 second = 1.7 degrees skew
2 seconds = 0.85 degrees skew
3 seconds = 0.57 degrees skew
4 seconds = 0.42 degrees skew

In order to see the skew clearly, a fast shutter speed is required, like 1/2000 of a second. A slow shutter speed, like 1/120 of a second (or slower) would generate a blur that makes it hard to spot the edge and see the skew (tilt). Even then, with 3 second pans and longer times, its' going to be hard to spot the skew.


Of interest is the video Eric posted of one of his tests: (see the top message)
http://www.dvinfo.net/conf/showthread.php?t=112362&page=3

It takes 18 frames (0.6) seconds for any part of the image to move from right to left across the frame. This is a VERY fast pan and shows a skew of 2.8 degrees. On a still image it's easy to see, but it's a lot harder to catch when you look at the video.


NOTE: 1 ms = 1 millisecond = 1/1000 of a second.


Bob Diaz

 

[ESTEBEVERDE]

The reset takes place and then, 1/48 second later, the read takes place.

In the mean time, between the read and the reset, photons are accumulating ("integrating") on the sensor (for a total of 1/48 second on any given line). There's a brief period when neither resetting nor reading is happening anywhere on the chip - where the whole chip is open to the accumulation of photons*. That is to say that the "window" between resetting and reading the chip, that scans downward, is taller than the chip.

That's how the theory goes.


---
*this is the moment when it is safe to fire a flash in front of the camera, as the photons will fall on the entire chip at once, after it has been reset, and all of those photons will be read by the read operation which follows.

Flashing during read during read or reset operations will cause the dreaded "partial exposure."

I thought you had it down to a "fact". :grin:

...
It's not my "position" but a fact that one can easily derive from testing the camera, as I have....

In all seriousness matt, it's very interesting and great to see you and other figuring all this out. :beer: