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variable shutter speed


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#1 Valentina Caniglia

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Posted 19 May 2005 - 02:11 PM

Dear all,

I am shooting the first part of a film in 35mm. In one of the scenes I would like to change the shutter speed and achieve at 11-degree shutter.

I would like to know what is the calculation for T-stop compensation with the changing of the shutter speed (11 degree, 30 degrees ect.) and if I can use the Arri 535B to achieve such a process. If not what camera can use to do this operation?

Also, if anybody knows if there is any flickering problems in changing the shutter speed when you are using HMI's.

Thank You

Valentina Caniglia
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#2 Kevin Zanit

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Posted 19 May 2005 - 02:54 PM

You would be changing your shutter angle, not speed.

The compensation is just like F-stops, every time you cut 180 in half is one stop. For instance you would open up one stop with a 90 degree shutter, and two stops with a 45 degree shutter (or 4 for a 11.25 degree shutter).

What you are asking to do is be able to ramp your shutter angle.

I believe only a 435 can ramp to 11 degrees (in 15 degree steps). You will also need a FIZ (Focus, Iris, Zoom) controller to ramp the iris with the shutter angle.

To avoid flicker problems you will need to use flicker free ballasts because even if you ramp to a "safe speed", you will still ramp through non-safe speeds.


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#3 oscar jimenez

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Posted 19 May 2005 - 02:56 PM

Hi valentina.
Did you check on the 535 specs to see if it opens to an 11 degree shutter? so flicker shows up depending if the HMIs ballasts are electronic and on F.free mode or if tey are magnetic. There are safe shutter speeds and FPS speeds for magnetic ballasts. Consult American cinematographer manual, David Samuelson's Proffessional cinematographer's hanbook or go to the cinematography electronics web site, they have the Flicker free charts in their web site.
Good luck
Oscar
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#4 Kevin Zanit

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Posted 19 May 2005 - 03:05 PM

I just checked, the 535b can do 11 also.


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#5 Max Jacoby

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Posted 19 May 2005 - 03:48 PM

There is a difference between changing the shutter angle in mid-shot and while the camera is not running. On most cameras the shutter can be adjusted mechanically (i.e. while the camera is not running), but you need a camera with an electronic shutter do so while you are filming.

Cameras where the shutter can be adjusted in shot are:

Arricam ST and LT,
Arri 535A
Arri435 ES/Advanced/Xtreme
Panavision Millenium/XL/XL2
Panavision Platinum and GII (but only to 50°)

The 535B cannot since it has a mechanical shutter.

Edited by audiris, 19 May 2005 - 03:51 PM.

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#6 Nate Downes

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Posted 19 May 2005 - 04:05 PM

audris:

You forgot a few which also can change shutter in mid-shot:

Mitchell NC
Mitchell BNC
Mitchell GC

Note, these are the non-reflex'd Mitchell's.
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#7 Valentina Caniglia

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Posted 23 May 2005 - 11:12 AM

Thanks to everyone so much for your infomation. They were really useful.

Valentina
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