The Automatic Focusing of DMX Moving Head Fixtures

Abstract

Context:

Since its inception in 1986, DMX512 has become the primary method of controlling intelligent lighting. A standardised, universal system to control lighting fixtures, DMX512 (and related protocols such as Art-Net) allow all aspects of a fixture’s functionality to be accessed and controlled to suit the environment in which the light is located and operating. Although widely used for over 35 years, the accurate control of focus has seen little development with no ability to automatically control this as a fixture’s head is rotated, or its optical functionality altered. This results in a moving image often only being in focus at one point within a space, giving a poor visual experience.


Aims:

This work investigates the current solutions which exist to control focus before moving on to investigating the possibility of implementing an automatic system to control the focus of DMX512 lighting fixtures as they are moved around a venue with their various features used. Within this, the accurate modelling of venues, fixtures and focus will be analysed and implemented, with a proof of concept produced that can automatically refocus a test fixture in a venue.


Methodology:

Dedicated code and algorithms are created to model a room, position lights within this room, find their position and orientation, and automatically correct their focus to keep their projection in focus as they are moved. Throughout, a range of mathematical techniques including rotation matrixes, vector transformations, perspective transformations and array handling are employed. In addition, a range of consumer-level, readily available tools are used, including a lidar and digital angle gauge.


Testing:

The focusing system is tested in three key areas: the accuracy of finding fixture locations and rotations, the accuracy of focus in a range of scenarios, and how long it takes to set the system up. For each test, the focusing system is compared to the traditional methods of focusing fixtures with test images taken and a system created to automate the process of analysing these images with the aim of evaluating focus accuracy.


Results:

The testing shows that a system has been created which can successfully keep DMX lighting fixtures in focus as they are moved, and their features used within any given space. The system is universal (able to work with any lighting fixture), and it can interface with existing lighting-control software and hardware. Tests across a range of scenarios show that the system works quickly and to a level of focus accuracy that would be considered “excellent” by observers.


Conclusion:

The results obtained from the investigation clearly show the advantages which an automatic focusing system can bring to DMX512 operators working in all areas (theatrical, musical, artistic and others). It also highlights the disadvantages of such a system and explains how it can suffer from measurement error at various stages throughout the modelling process.


Future Developments:

As well as automatically controlling focus, the system could be expanded to allow for other lighting techniques to become available including follow spot functionality, automated gobo size control, the ability to point fixtures at certain positions within a venue without their pan/tilt parameters having to be set, the correction of non-linear movement and velocity, and focus control of a tracked live performer.