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What is the use of a video assist?

I've seen Cinematographers using the IVS Video assists on their Arri cameras. Is it a preview system independent of what has been captured by the film?
 
You can't review what's been captured by film before it's been processed. That's why the video assist was invited. You review the video instead.
 
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When shooting film negative, exposing a frame to light exposes the film, and then to view the footage back you need to process (develop) it - exactly like how your old negative film still cameras worked.

The purpose of the shutter is to block light hitting the film whilst the frame increments. The purpose of having a mirror on the shutter is so the image is mirrored into the eyepiece so the operator can see what he's doing.

Of course in the early days of film, cameramen were their own operators, and sometimes their own Directors - and when they weren't Directors either trusted their cameraman to frame, or looked down the viewfinder as often as possible to ensure the frame is to their liking.

Looking down the viewfinder is not the easiest way of doing anything, and with many more people needing to see the frame (i.e. the Director, the DP to see what his operators are framing, Production Designers etc. etc.), there needs to be a better way than having multiple people look down a number of viewfinders.

Enter the Video split/video assist. What it does is sit a small digital camera inside the film camera. It takes a 'split' image off the mirror, and converts that into a digital signal that can be viewed externally. Many of the more modern film cameras shipped with digital Video Assists already installed - older cameras needed to have them installed. It was cheaper to get black and white Video Assist's installed, which is why many are black and white.

This means a BNC cable can be run from the camera to a Video Village and many others would be able to see the frame being recorded. In many cases, as the technology modernised, could be run to a portable tape deck, so that takes could be recorded and played back instantly on set.

Dailies would still be screened, as Video Assist is good for framing, but you cannot judge much else (like lighting, exposure, focus) on it.
 
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Well, yeah! Its pretty hard to determine the exposure and focus on viewfinders, video assists and even the LCD viewfinders that come with Digital cameras, they are so misleading. A lot depends on the eye and the mind of the cinematographer, an intution - so to speak :) So yeah, as you said, viewfinders should only be looked at as a framing tool.
 
Well, yeah! Its pretty hard to determine the exposure and focus on viewfinders, video assists and even the LCD viewfinders that come with Digital cameras, they are so misleading. A lot depends on the eye and the mind of the cinematographer, an intution - so to speak :) So yeah, as you said, viewfinders should only be looked at as a framing tool.

With film cameras, you're only getting a feed of what a tiny little, often black and white camera sees. Exposure is usually determined via copious use of a light meter. With digital cinema, you get a signal straight from the sensor, which means what you see is literally what you're getting. Usually, the signal is in 1080p, or even 4k, which means it's possible to judge focus (especially with the advent of focus peaking). Judging exposure is still done in some way via light meter, but usually more focus is on what it looks like on the monitor, especially employing tools like False Colour, and the Waveform Monitor, to judge exactly where the exposure is sitting. With the advent of on-set DITs, and calibrated monitors with LUT files applied, these days what you see on the Video Village monitor on set can be exactly what ends up being projected all over the world.

It's certainly possible, and often done, to judge colour, exposure and lighting off a monitor on most digital cinema cameras. Certainly, ACs tend to get their own personal monitors these days, in case they'd like to get some marks off the monitor. Generally, the small monitors ACs get (at least the smallHD ones) are not very good for judging colour and exposure, unless properly calibrated.
 
Invented by Jerry Lewis to aid him whilst both directing and acting so he could check his framings without having to jump behind the camera while in makeup and costume.
 
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