Shutter Angle?

[Mathieu Ghekiere]

Hi,

I've just received my Sony EX1, and I have seen that I'm not in control over the Shutter Angle. Can anyone tell me what the visible difference is if you change it, why you would change it, and what would be the best option if you are going for a filmic narrative look?

Thank you very much in advance,

[Mathieu Ghekiere]

I've read some trough the boards... If I'm correct, for a more filmic look I should go with the 180 degree shutter angle?

[Greg Boston]

Originally Posted by Mathieu Ghekiere

I've read some trough the boards... If I'm correct, for a more filmic look I should go with the 180 degree shutter angle?

That's the normal angle. If shooting 24P, it equates to 1/48 second. The 180 degree number comes from the mechanical shutter on the front of a film camera that rotates two revolutions for each frame of film. The circle is half open/half closed (180 degrees of a circle). Each film frame gets exposed twice at a 1/48 second differential in time.

Again, that's just for the standard rate. Other combinations are possible.

-gb-

[Serena Steuart]

>>>mechanical shutter on the front of a film camera that rotates two revolutions for each frame of film<<

No it doesn't; you are thinking of a projector, which has two openings per revolution. In a film camera the essential function of the shutter is to be closed while the film is advanced. In a simple mechanism the film is advanced during one half revolution of the shutter shaft, so the other half is available for exposure. So at 24fps the drive is running at 24 rps, hence 1/48 second. Often smaller shutter angles are used.

If you're not accustomed to using shutter angles (ie a film cinematographer) switch the EX to exposure time (1/48, 1/60, etc).

[Mike Stevens]

Yes, as Serena implies "shutter angle" is just another way of describing "shutter speed" for they both equate to length of each exposure. 180 deg is half of a full circle and means you get 50% of the maximum of if the shutter were always open so with 24p that equates to a shutter speed of 1/48.

Setting your shutter speed to 1/48th with 24p is exactly the same as setting the shutter angle to 180.

IF with 24p you wanted to double the exposure so you had the full 1/24th of a second for every frame of the 24, IE a shutter angle of 360deg, then you just turn the shutter OFF with the little slider switch near the white balance button on the front of the camera.

Mike

[Sean Donnelly]

I know this is trivial, but Panaflex cameras have used a shutter with two openings, the mirror segments are 80 degrees wide and placed opposite each other which means the mirror only has to spin half as fast, and allows for a 200 degree shutter.

-Sean

[Michael Mann]

So shutter "angle" does or does not mean that the sensor is read out in a way that simulates the exposure which results from the REVOLVING sector of a film camera?
Can anyone please confirm this.

[Greg Boston]

Originally Posted by Serena Steuart

>>>mechanical shutter on the front of a film camera that rotates two revolutions for each frame of film<<

No it doesn't; you are thinking of a projector, which has two openings per revolution. In a film camera the essential function of the shutter is to be closed while the film is advanced. In a simple mechanism the film is advanced during one half revolution of the shutter shaft, so the other half is available for exposure. So at 24fps the drive is running at 24 rps, hence 1/48 second. Often smaller shutter angles are used.

Mea culpa. Here's a wiki link that explains and animates it.

http://en.wikipedia.org/wiki/Rotary_disc_shutter

-gb-

[Eric Pascarelli]

Michael,

Yes, that's what it means. It uses the same convention as a revolving shutter film camera (not a projector as Serena correctly pointed out).

180/360 = 1/2

Half of the frame time is spent exposing the sensor/film. The other half is blanked.

So at 24fps, (a frame exposed every 1/24 second) 180° shutter, the exposure is 1/48 second.

[Michael Mann]

Greg, Eric, I think there is still a misunderstanding:
Are you sure the sensor is read out exactly the way a rolling shutter exposes a frame (angular direction from top left to bottom right corner of the sensor)?
Or is it just a normal linear read out instead (straight horizontal or vertical movement) - the way the shutter of a SLR exposes a frame?

[Eric Pascarelli]

Originally Posted by Michael Mann

Greg, Eric, I think there is still a misunderstanding:
Are you sure the sensor is read out exactly the way a rolling shutter exposes a frame (angular direction from top left to bottom right corner of the sensor)?
Or is it just a normal linear read out instead (straight horizontal or vertical movement) - the way the shutter of a SLR exposes a frame?

It is read out linearly, definitely. From top to bottom of the image (bottom to top of the sensor)

The shutter angle is just a convention used to refer to the proportion of time open to time closed per frame.

BTW, there is no set convention for shutters on film cameras. Most Arris have the spinning shutter below the gate, while Panavisions usually sit to one side of the gate. This yields very different sweep patterns over the film plane.

[Paul Kellett]

http://en.wikipedia.org/wiki/Rotary_disc_shutter

[Michael Mann]

Thanks, Paul and Eric, for the clarification.
Yes, it was the "sweep pattern" of the EX1' sensor read out that I was interested in.

[Greg Boston]

Originally Posted by Paul Kellett

http://en.wikipedia.org/wiki/Rotary_disc_shutter

Hehe. Paul, I posted that same link just above.

-gb-

[Simon Wyndham]

The real reason you would want to use the shutter angle on the EX1 is for variable frame rates. By setting it to 180 degrees you will guarantee the correct shutter for good slow motion no matter which framerate you use. Otherwise you would have to calculate things manually (and there isn't enough selections of fractions of a second style shutter to account for every frame rate combination anyway). So in short, use fractions of a second for normal shooting, and shutter angle for variable frame rate.