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> Exposure Compensation While Ramping Speed

>Published : 15th January 2009

>Hello Everybody,

>I'm about to shoot a film in which I am planning to ramp speed during the shot. My initial intention was to get a camera which will support exposure compensation with the shutter angle, such as a 435, but as I'm given an Arri 35-3 for this, someone suggested I use a system which connects externally to the camera controls, and corrects the aperture in real time to compensate exposure while the speed is changing.

>Is anyone familiar with this device and where this can be rented? Has anyone worked with this and can say that it actually does this in a transparent way?

>There is also the theoretical issue of the effect of changing the aperture vs. changing shutter angle which I'm still thinking about. The correction will be about 3 stops.

>Any thoughts on this will be greatly appreciated.

>Thanks!

>Tal Lazar
2nd year Cinematography Fellow
American Film Institute Conservatory
http://www.talazar.net


>Hey Tal,

>I've shot with the Preston system that Clairmont rents and it is seamless and easy to use. You calibrate the stops on the lens, set the parameters, and let're rip.

>Mark Woods
Director of Photography
Pasadena, California
www.markwoods.com


>Tal Lazar wrote:

class="style19">>>Is anyone familiar with this device and where this can be rented?
>>Has anyone worked with this and can say that it actually does this in a transparent way?

>Many years ago Howard Preston cooked up a box that would do just this.

>Pre Arri 535 and 435. It used a Microforce motor on the lens T Stop ring and had to be calibrated to the lens in use. It was a bit clunky but worked very well. I even worked on one shot with an Arri BL4 on a Steadicam (!!) using this to do a speed ramp while moving across a school playground. He may still have it kicking around for rent. I think I remember using it with an Arri 35-III as well. Contact them at: www.prestoncinema.com/contact.html

>Doing an iris / speed ramp, you are dependent on the "slop" in the iris ring of the lens and whether the iris gives the same value when moving in the "stop down" or "open up" direction. Not always guaranteed.

>Rod Williams
Motion Picture and HD First Camera Assistant
Petaluma, California
U.S.A.


>This sounds like a job for the Arri ICU.

>I know that Camera Engineering in the UK (I'm a big fan of them.) Had a box that would ramp an XTR, and connect to the Arri ICU for Exposure change.

>Although that is Super 16, and not an Arri 35 III, but it can be done.

Steven Gladstone
New York Based Cinematographer
Gladstone films
http://www.gladstonefilms.com
917-886-5858


>I missed the beginning of this thread, but the Preston Speed Aperture Controller does this with an Arri 3 to the best of my recollection - you put a motor on the lens iris and the box ramps the motor while countering the iris.

>Can be set up to work with a number of different cameras, but I have used it
with Arri 3 and the older Fries VistaVision cameras.

>Mark Weingartner
LA based VFX DP


>I have used this 'Iris' ramping device serval times. In my opinion it works ok (if as already mentioned here) you calibrate and set the iris stops, but the only thing which makes it (in my opinion) a second choice against a camera where you can change the shutter angle, is the change is depth of field. If is not noticeable then great, but for some shots, it was distracting. Only my opinion.

>Adrian Cranage
Director of Photography
Frankfurt/Germany
EU Based

>www.cranage-dop.com


>Thank you all for your replies.

>I had two concerns using the Preston system for ramping: accuracy ( which seems fine according to all of the responses) and the dilemma between compensating with aperture or shutter.

>Ramping down from, lets say, 96fps to 24fps and compensating by either closing down two stops or by changing the shutter angle down to 45' is something completely different, and I wonder what is more noticeable in a shot where a camera moves fast.

>Tal Lazar
2nd year Cinematography Fellow
American Film Institute Conservatory
http://www.talazar.net