Automated lighting fixtures are extremely sophisticated, to the point that some people even refer to them as “intelligent.” While the fixtures are packed full of very smart features, they actually require a human with a bit of knowledge to operate them properly. This is very true when it comes to controlling the movement of pan/tilt or other features. Fixtures and consoles provide a multitude of methods to ensure that these movements are either perfectly smooth or extremely quick. A thorough understanding of the various options is imperative for any automated lighting programmer.
» Smooth Fixture Movements
Most automated lighting fixtures are set by default to move their pan and tilt parameters as smooth as possible. The engineers who created the light will use powerful algorithms to accelerate and decelerate the fixture depending on the size and weight of the moving head (or mirror). When you command the light to move from point A to point B on stage, the light will (hopefully) ramp up to full speed and slow down to a nice smooth stop. Usually these changes in speed are not noticeable to the naked eye and the light just appears to move nicely. However, if you are manually moving the fixture via a console trackball or encoder, you might think the fixture is lagging behind your adjustments a bit. This is because the fixture software is trying to anticipate the commands you are sending via DMX and smooth out the transitions between values. Once programmed into the console, the rate of changing DMX values becomes consistent during a programmed crossfade, and thus the fixture software can better anticipate the changes and move in a very smooth manner.
Although you might want the smoothest movement possible most of the time, fixture designers also provide us with tools to change the behavior of the fixture and allow it to move differently. The most common method is to provide a DMX value to “turn off” the smoothing algorithm. Several manufacturers accomplish this by providing a “toggle” within the fixture’s movement timing channel. With a DMX value of 255 the fixture will move smoothly, but not as fast as possible. This is because it is looking at the DMX values sent to it and determining a pattern. Then the fixture will move with acceleration and deceleration to smooth the movement. However, if you set the same channel to DMX zero, then the fixture will move as fast as possible but, depending on the movement distance, it might be a bit steppy or have a bounce at the end of the movement.
Some other manufacturers have done away with timing channels altogether and just offer a toggle in the fixture’s control channel that allow to you select normal, fast, or slow movement.
» It Is Not All About the Fixture
It is important that you understand the options available from a fixture, because there is yet another piece of the puzzle involved. Your lighting console will typically use a fixture library (or profile), which defines default values for each and every DMX parameter used by the fixture. If your console defaults the particular movement timing channel to DMX zero, then your fixtures are going to move quickly, but may not be smooth. On the other hand, if the console defaults your timing channel to DMX 255, then the fixture will move smoothly, but not as fast as physically possible. Again, it is essential that you understand the timing channel options and how they are defaulted within your console’s fixture library. Then you must also be sure to know how (and when) to change the value for the timing or control channel to get the type of movement you desire. In some rare cases, you might find that your console library has not implemented these features and you may not have access to the specific channels. You will then need to adjust your fixture library or contact your console support for assistance.
With some fixtures, the same principles used for smoothing pan and tilt movement can apply to other parameters as well. For instance, a fixture with framing shutters may utilize movement smoothing as most users want shutters to move smooth and slow. However, if you want to create a stunning fast shutter chase, then you need to understand how to disable the smoothing so that the shutters can move as fast as possible. Usually this is accomplished via a similar method to pan/tilt with a toggle in the beam timing channel or a control channel. As always consult your fixture’s user manual for specific details about parameter timing.
» Speaking of Timing Channels
There are two ways to control the time of changing parameters on an automated lighting fixture. One is to allow your lighting console to take control of all the timing and just send crossfading DMX values to the fixture. In this case, if you instruct the fixture to dim from 0 to 100 percent in five seconds, a constant stream of changing DMX values from the console will increase from 0 to 255 over five seconds. The fixture will then respond accordingly and output more light in these increments. This type of timing is easy to coordinate with other fixtures in the console and other console events. Furthermore, it allows for greater control when commands need to change. For example, if you pause your console’s crossfade, the DMX flow will also stop, and the fixture will instantly hold at its current dim value. The only downside is that you are limited to the resolution of DMX, and this can cause jittery movements of fixture mechanisms with long crossfades. Imagine trying to adjust a parameter with 256 steps over 10 minutes!
Many fixtures contain timing channels that can be activated to allow the fixture itself to calculate the rate at which a mechanism moves. This allows for a much finer resolution than is available via DMX. Instead of the console streaming DMX changes, the console sends an instantaneous DMX change and a timing instruction to the light. So, if you wish to dim the fixture from 0 to 100 percent in five seconds, you will tell your desk to change at a zero crossfade time, but set the fixture’s timing channel to a DMX value equivalent to five seconds. Now the fixture will see the instant change and know that it needs to change its dimmer level to 100 percent, and over what amount of time. The internal fixture software can then move the mechanics as smoothly as possible within the allotted time. While this method does produce the best movements, it also does have a few drawbacks, such as not being able to be easily paused. If, after two seconds, you want to pause the timed change, you would need to send a new DMX value equal to the current position of the dimmer. Unfortunately, you will have no idea what this value is at any given moment. The tradeoff, though, is perfectly slow movements. Fixture-based timing is best used for extremely long changes that appear steppy when crossfaded via DMX.
» Smoother Yet
Some programmers like to enable a small amount of movement timing from a fixture just to further smooth out a fixture’s movement. Sometimes you might come across a fixture that bounces as it comes to a stop. By simply adding a 0.7s time to the fixture’s movement channel, it will cause the fixture to react a bit slow to the stream of DMX values, and thus cause smoother movements and stops. Smooth moves are an essential part of automated lighting, just as much as extremely quick movements. Automated lighting programmers should understand the options and functions available on their fixtures and consoles to ensure their programming is always as smooth as possible.
