Motion control photography

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Motion control photography is a special effects technique used in films that enables the same camera or object movements to be exactly repeated in different recordings using computer-aided automation. In post-processing, the recordings can be combined into a compositing. This enables effects that were previously impossible in recordings with a moving camera, for example that the same actor appears several times in a picture or that models and real recordings (by scaling the camera movement) can be connected to one another in tracking shots or pans. Motion control photography ( MoCo for short ) was first used on a larger scale in Star Wars (with the Dykstraflex system) and played a major role in making this film a landmark in visual effects. Since then, motion control photography has become a standard technique used in all types of film.

Development and way of working

Model making has a long tradition in the film industry. However, if a model is too small, it often loses its illusion and becomes "obviously a model". To solve this problem, it makes sense to simply build larger models, but this creates other problems, as large models are more difficult to move and more fragile. Another approach is to move the camera instead of the model. However, this is not easy either, since cameras are large and heavy devices that are difficult to move in many cases as if moving the model yourself.

The problem can be avoided in part by running the movie at a higher speed, moving everything quickly, and later playing back the scene at a slower rate. This results in significantly smoother movements that can be fooled by the eye, but is very expensive to set up and operate because special equipment is required, particularly high speed cameras .

The real solution was to mount the camera firmly and to move either the camera or the model very precisely with a motor-driven frame. The first indications that this was possible came from John Whitney , who invented various movement techniques using old analog computers . These devices were originally built to control anti-aircraft guns . Whitney connected them to servo motors to control the movement of lights and illuminated targets.

By reversing the system by replacing the targets with a small camera, the first motion control frames were created . The camera could now be moved very precisely and fluidly past any model of any size, and the illusion was far more convincing.

Cons and Problems

The downside to motion control photography is that it takes quite a bit of programming to get the camera to move as you imagine it to be. This was a serious problem in the 1970s, but until the 1990s, the increasing power and usability of computers made this fact negligible. The great technical and qualitative advances in the field of Computer Generated Imagery (CGI) have meanwhile led to the replacement of motion control photography by CGI in many areas. Cost considerations in particular play a role here: With CGI, complete scenes can now be created efficiently on the computer, whereas motion control requires a not inconsiderable amount of effort for model building, filming and post-processing; For example, in order to be able to work with light and shadow in the finished scene (two elements that are very important for a convincing illusion), several runs of the same scene must be shot. This can be one run under normal light, several with individually darkened light and possibly further runs under UV light , for example, to be able to realize luminous windows on models. The material from all these scenes is then later overlaid, put together and post-processed. It is obvious that CGI has advantages on the other hand, since only one scene has to be created and the correct shadows can be calculated by the computer.

Future and further developments

The motion control system is experiencing a renaissance in film tricks. Since compositing is becoming more and more important in special effects, you need precise, repeatable camera movements. With manual operation, i.e. by cameramen, the necessary precision for millimeter-precise movement and exact setting of the camera, such as focus and aperture, cannot be achieved. With motion control, however, tricks can be implemented that were previously only possible with a static camera. The duplication of a figure can also contain movement thanks to motion control.

Another important feature of newer motion control systems is the ability to read out the data and then process it further in 3D programs. For example, real recordings of actors can be combined with CGI material such as backgrounds or masses of monsters.

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