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What does it really mean to shoot open gate?

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#1 davide sorasio

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Posted 25 June 2016 - 09:45 PM

Hi everybody, I'm looking for more explanations on shooting open gate. Arri's website says that shooting arri raw open gate gives you a frame size of approximately 3.4 K with a 1: 1.55 aspect ratio. Why is that an important feature? To gain more pixels by recording on a bigegr sensor?Is this mode especially convenient with anamorphic? and is that aspect ratio the "final" aspect ratio of the image?

Also, reading the latest American Cinematographer the DP talking about previously shooting open gate arri raw with anamorphic and then shooting on spherical lenses and not using the open gate mode said" we wanted to get really close to the actor, so we used spherical lenses and only part of the sensor so it was easier to shoot and be more flexible". I do not see the relationship between shooting/not shooting open gate and the possibility to get closer to a subject.


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#2 David Mullen ASC

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Posted 25 June 2016 - 10:45 PM

Open Gate has no value if shooting with 2X anamorphic lenses because you use a 1.20 : 1 sensor area to get a final 2.40 : 1 image -- so the wider Open Gate doesn't help.

 

However for spherical 2.40 and 1.85 movies, Open Gate gets you slightly more resolution in raw, 3.4K instead of 2.88K.  An analogue version would be like the improvement of Super-16 over regular 16mm, or Super-35 over regular 35mm.

 

I'm not sure if you've gotten confused by the AC article because you wouldn't need to shoot Open Gate for anamorphic unless they meant 1.3X Hawk anamorphic lenses were used, or they meant that they recorded Open Gate for everything whether or not they used spherical or anamorphic lenses (cropping the sides for 2X anamorphic and cropping the top & bottom for spherical 2.40).  

 

But in terms of anamorphic versus spherical, many spherical lenses have a closer minimal focus than anamorphic lenses.

 

No, 1.55 : 1 isn't the final aspect ratio unusually since most projects are either 1.85 or 2.40 for theatrical, 1.78 : 1 for TV, though there are some exceptions.  IMAX film projection is 1.45 : 1 so I guess a 1.55 : 1 recorded image would be useful.  But generally you'd compose to extract 1.85 or 2.40 from the 1.55 Open Gate image.

 

Similar to what happens in film -- 4-perf 35mm is 1.33 : 1 Full Aperture, and 3-perf 35mm is 1.78 : 1 Full Aperture, and often these formats are used for 1.85 or 2.40 movies.  Sometimes it is helpful when your recorded format is taller than the extracted final aspect ratio because it gives you some flexibility to reframe or stabilize a frame.


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#3 davide sorasio

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Posted 27 July 2016 - 08:09 PM

Thanks a lot David, this helps me a lot! But I still have some doubts. If you look at the attached image, taken from the Arri Nab 2016 Issue, where they talk about the SUP 4.0 and possibility of shooting open gate and anamorphic on the sensor, I cannot understand why 16:9 is not wider than 4:3!
16:9 means 1:1.78, so the height is 1 and the width is 1,78 times the height. 4:3 means 1:1.33, so it' should be more similar to a "square", but if you look at the image attached it's kind of the opposite, having 4:3 wider than 16:9.
What am I not understanding??

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#4 David Mullen ASC

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Posted 27 July 2016 - 08:49 PM

That line goes to "16x9 HD Ana" -- it's a very skinny vertical rectangle -- a .8888 : 1 area so that if you shoot with a 2X anamorphic lens, once you unsqueeze the image by 2X horizontally in post, it becomes 1.77 : 1 (16:9). It's for people who just want the lens artifacts of a 2X anamorphic lens but want to end up with a 16:9 image. That chart you posted shows no normal 16:9 recording area.

 

When the sensor is overall 1.55 : 1 (Open Gate) then 4:3 would share the same height but be slightly less wide... and a normal 16:9 area would be shorter in height than 4:3.

 

You can see some other charts here:

ALEXA_Mini_SUP_4_-_RecordingAreas-P1.jpg


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