Shutter speeds in 25p mode

Steven Thomas · January 4th, 2008, 10:51 AM

I have not see not seen this. I had a real concern since I shoot concert lighting. Most of my lights have MSD lamps. I have not checked out my LED panels with the EX1. These are the type of panels they use as backdrops on stages.
My other video cameras (HD100, global shutter) flicker when shooting these panels.
It mainly has to due the dimmer function with LEDs using PWM (Pulse Width Modulation). It's essentially a duty cycle for controlling light output.

The flicker can be reduced quite a bit by timing adjustments in the DMX control circuit for these LEDs, nonetheless, as we know, all video cameras can suffer from issues causing flicker.

It will be interesting to see how the EX1 works with these LED panels.

Raymond Schlogel · January 4th, 2008, 01:08 PM

Hey Paul, thanks for the clarification, glad there was a reason to the assumptions I've been working under even though I don't remember the source!

Okay, in my thirst for knowledge, how does angle fit into this equation? As you said "which does the same thing but also changes with framerate", does that mean that in your example of "If however you increased your frame rate to 48p ... you would also need to increase shutter to 96." If I were using angle instead of 1/48 that it would do this automatically? If so, then in 24p, what would be my desired angle?

So much to learn!

- Ray

Eric Pascarelli · January 4th, 2008, 01:52 PM

Raymond,

The angle setting sets up a relative rather than absolute shutter duration.

It's based on the film tradition of the shutter being a essentally a spinning pie chart, spun by a motor at a constant speed (the frame rate). Here's a good schematic on Wikipedia:

http://en.wikipedia.org/wiki/Image:M..._animation.gif

(thanks to Anthony at IEBA Tech Thoughts for the link)

Film cameras can only open their shutters to expose film around half of the 1/24 seconds alloted to each frame (1/48 second) because the other 1/48 second is needed to move the film though the gate and register it for the next exposure.

Because a circle is 360° around, this half-pie opening is considered to be a 180° opening.

Since this is a mechanical constant in a film camera, speeding up a film camera to, say 48fps, (by spinning the motor twice as fast) will allow 1/2 of the time (1/96 second) for exposure and the other 1/96 second to "pull down" the film.

Likewise 60fps (achieved by spinning the motor faster still) creates a 1/120 second exposure and 1/120 second pulldown.

Most film cameras have variable shutters. To create a shutter opening that is 1/4 of the time alloted to each frame, one would need to close the pie opening down to 90°. At 24fps this would create an exposure of 1/96 second. At 48fps it would be 1/192 second and at 60 it would be 1/240 second.

The EX1 allows one the option to use this film paradigm to set the shutter duration. When set to 180°, the shutter will always be one half of the duration alloted to each frame. When set to 90° it will always be 1/4 of the duration. When you change the frame rate in the EX1 when in the shutter angle mode, the shutter duration will change proportionally.

Although not a perfect representation of motion, we have gotten used to the 180° shutter and its half-exposure, half-non-exposure ratio and associate it with a film look.

One thing that video cameras allow that film does not is the ability to open the shutter beyond 180°. Turning the shutter off on the EX1 creates the look of a 360° shutter, an impossibility in film. I think as we use this 360° shutter more and grow accustomed to the larger amount of motion blur, this will become a more desirable shutter setting.

January 4th, 2008, 01:08 PM	#17
Raymond Schlogel Regular Crew Join Date: Sep 2004 Location: Austin Texas Posts: 162 Images: 3	Hey Paul, thanks for the clarification, glad there was a reason to the assumptions I've been working under even though I don't remember the source! Okay, in my thirst for knowledge, how does angle fit into this equation? As you said "which does the same thing but also changes with framerate", does that mean that in your example of "If however you increased your frame rate to 48p ... you would also need to increase shutter to 96." If I were using angle instead of 1/48 that it would do this automatically? If so, then in 24p, what would be my desired angle? So much to learn! - Ray __________________ www.undergroundplanet.com

January 4th, 2008, 10:51 AM	#16
Steven Thomas Trustee Join Date: Sep 2005 Location: Gilbert, AZ Posts: 1,896	I have not see not seen this. I had a real concern since I shoot concert lighting. Most of my lights have MSD lamps. I have not checked out my LED panels with the EX1. These are the type of panels they use as backdrops on stages. My other video cameras (HD100, global shutter) flicker when shooting these panels. It mainly has to due the dimmer function with LEDs using PWM (Pulse Width Modulation). It's essentially a duty cycle for controlling light output. The flicker can be reduced quite a bit by timing adjustments in the DMX control circuit for these LEDs, nonetheless, as we know, all video cameras can suffer from issues causing flicker. It will be interesting to see how the EX1 works with these LED panels.

January 4th, 2008, 01:52 PM	#18
Eric Pascarelli Major Player Join Date: Nov 2007 Location: Los Angeles, CA Posts: 498	Raymond, The angle setting sets up a relative rather than absolute shutter duration. It's based on the film tradition of the shutter being a essentally a spinning pie chart, spun by a motor at a constant speed (the frame rate). Here's a good schematic on Wikipedia: http://en.wikipedia.org/wiki/Image:M..._animation.gif (thanks to Anthony at IEBA Tech Thoughts for the link) Film cameras can only open their shutters to expose film around half of the 1/24 seconds alloted to each frame (1/48 second) because the other 1/48 second is needed to move the film though the gate and register it for the next exposure. Because a circle is 360° around, this half-pie opening is considered to be a 180° opening. Since this is a mechanical constant in a film camera, speeding up a film camera to, say 48fps, (by spinning the motor twice as fast) will allow 1/2 of the time (1/96 second) for exposure and the other 1/96 second to "pull down" the film. Likewise 60fps (achieved by spinning the motor faster still) creates a 1/120 second exposure and 1/120 second pulldown. Most film cameras have variable shutters. To create a shutter opening that is 1/4 of the time alloted to each frame, one would need to close the pie opening down to 90°. At 24fps this would create an exposure of 1/96 second. At 48fps it would be 1/192 second and at 60 it would be 1/240 second. The EX1 allows one the option to use this film paradigm to set the shutter duration. When set to 180°, the shutter will always be one half of the duration alloted to each frame. When set to 90° it will always be 1/4 of the duration. When you change the frame rate in the EX1 when in the shutter angle mode, the shutter duration will change proportionally. Although not a perfect representation of motion, we have gotten used to the 180° shutter and its half-exposure, half-non-exposure ratio and associate it with a film look. One thing that video cameras allow that film does not is the ability to open the shutter beyond 180°. Turning the shutter off on the EX1 creates the look of a 360° shutter, an impossibility in film. I think as we use this 360° shutter more and grow accustomed to the larger amount of motion blur, this will become a more desirable shutter setting.