Basics 7. The moving head: pan, tilt, gobo, prism, zoom

The moving head is the most spectacular fixture there is and the most baffling for a beginner. It has a couple of dozen channels, half of them named things like Gobo Shake and Prism Rotation. Let’s take it apart: movement first, optics second. After that the channel table of any head will read like an open book.

Pan and tilt: two motors, two axes

Pan is rotation around the vertical axis — «left and right». Tilt is the nod — «up and down». The entire position of the beam in space is set by those two numbers.

Fig. 1 — The axes of a moving head: pan horizontally, tilt vertically
Fig. 1 — The axes of a moving head: pan horizontally, tilt vertically

On most models the ranges are:

Axis Typical range What it means
Pan 540° (sometimes 630°) One and a half turns: the head can look backwards and come back the other way
Tilt 270° (sometimes 180°) From «back and up» through «straight down» to «forward and up»

Channel value 0 is one end of the travel, 255 the other, 128 roughly the middle. On most heads pan = 128, tilt = 128 points the beam straight down (or straight ahead — depends on the model): a convenient «home» position for testing.

⚠️ Careful: 540 degrees is one and a half circles, not one and a half «routes to the point you want». If the head is at its extreme left and you ask it to go to the extreme right, it will travel the whole way — that takes a second or two and is very visible on stage. A professional habit: before a number, pre-position the heads on the side the movement will start from.

Smooth movement: 16 bits and the speed channel

Remember 16-bit channels from lesson two? The moving head is their main customer. If pan is spread over 256 steps, one step is about two degrees: at 15–20 metres that is a visible jump of the beam. So heads have Pan Fine and Tilt Fine channels — with them there are 65,536 steps and the movement looks genuinely smooth.

Separately there is a speed channel (Pan/Tilt Speed, Movement Speed, Speed). It tells the fixture itself how fast to execute a command:

  • a value of 0 usually means «as fast as possible» — the head snaps across;
  • higher values slow the movement down and make it smooth.
💡 Tip: the speed channel has a catch. If the fixture is slowing the move down and the software is also fading between positions, the two effects stack and the head starts to lag — visually «drifting» and missing the beat. Practical rule: speed is controlled in one place only. Simplest is to leave the speed channel at «fast» and handle smoothness in the software.

The head hangs upside down: inversion

Heads are almost always rigged on truss or ceiling facing down. That flips the tilt axis: «up» now lowers the beam, and mirrored fixtures drift apart instead of together.

There are three ways to fix this, and all three are used in practice:

  1. Setting in the fixture. The menu has items like Pan Invert, Tilt Invert, and sometimes a ready-made Hanging / Inverted mode.
  2. Setting in the software. A tick box in the fixture’s properties inverts the required axis.
  3. A mirrored pair. For symmetrical fixtures left and right, pan is inverted on one of them — then they open out and close in together, as in a mirror.
💡 Tip: settle on one method for the whole rig and write down which one. Otherwise, a month later you will be puzzling over why one head out of four behaves differently — and it will turn out that its inversion is switched on twice and therefore does nothing.

Optics: what the head draws with

Next comes the set of «tools» inside the fixture. Not every head has all of them, but the channel names are standard.

Fig. 2 — What gobo, prism and zoom do to the beam
Fig. 2 — What gobo, prism and zoom do to the beam

Gobo — a metal or glass stencil placed in the beam to draw a pattern: dots, stars, stripes, a logo. Gobos sit on a wheel, and the Gobo channel works as a list, just like the colour wheel: each pattern has its own value range. The neighbouring Gobo Rotation channel spins the chosen stencil one way or the other, or holds it at a set angle. Often at the top of the gobo channel’s range there is shake — the stencil starts to judder, an effective trick for fast tracks.

Prism — a glass attachment that multiplies the beam into 3, 6 or 8 copies. Usually comes with its own rotation channel. Combine «narrow beam + gobo + prism + haze» and you get that classic «outer space» over the dance floor.

Zoom — changes the beam angle: from a narrow column to a wide wash. One of the most useful channels: the same head can work as a beam or as a wash.

Focus — the sharpness of the pattern. Out of focus a gobo is a blurry blob; in focus it is a crisp design. The right focus depends on the distance to the surface, so it is trimmed on site.

Iris — a mechanical diaphragm that narrows the pool without changing the angle. Lets you do the «contracting beam» effect.

Frost — a diffusion filter that softens the beam’s edges. Turns a hard spot into a soft wash.

Shutter — already familiar from lesson four: closed, open, strobe. On lamp-based heads the shutter is the only way to kill the beam instantly, because the lamp itself does not switch off.

Housekeeping channels and the ailments of heads

At the end of the channel table there is almost always a housekeeping channel — Reset, Special Functions, Control. Typically, at a value around 200–255 (held for a couple of seconds) the fixture restarts its motors: the head buzzes, runs through its axes and returns to its start position. That is the first remedy when a head gets lost.

Typical problems and what is behind them:

Symptom Likely cause
The head went somewhere you did not ask for Motors lost their step — run a Reset
All heads point the same way except one It has different inversion or a different channel mode
Movement is jerky, in steps No 16-bit mode, or a profile without fine channels
The head lags behind the music The speed channel is set to slow movement
The head hums and does not move Mechanical failure or a seized motor — take it down for repair
There is a beam but no pattern Out of focus, or the gobo sits in an «empty» position
💡 Tip: before every event let the heads run a Reset and drive them through their extreme positions. Two minutes of checking beforehand beats a surprise in the middle of a number.
⚠️ Careful: do not move the head by hand while the fixture is powered — you can damage the mechanics. Carry and rig heads by the base, never by the moving part.
📍 How this looks in SvetoMaster: the head’s position is set with the mouse rather than with numbers — the 3D visualiser shows where the beam will land before the fixtures are even in the room. Positions you like are saved as position presets and later assembled into scenes. For movement there are ready-made effects (circle, figure of eight, wave and others) with adjustable size and speed, and the program handles the 16-bit channels itself.

Key points

  • Pan is rotation (usually 540°), tilt is the nod (usually 270°); 128 on both axes is a handy «home» point.
  • Smooth movement comes from the pair of Fine channels; the Speed channel controls speed at the fixture — do not fight it from the software.
  • Rigging upside down calls for inversion — apply it one single way across the whole rig.
  • Gobo draws the pattern, prism multiplies the beam, zoom changes the angle, focus the sharpness, iris narrows the pool, frost softens the edges.
  • The Reset housekeeping channel restarts the motors — first aid for a lost head.
  • Beams are only visible in haze — without atmosphere half of a head’s capability is wasted.

Coming next: the most practical subject in the course — cables. Which cable is suitable for DMX and which is not, why fixtures are wired in a chain, what that mysterious terminator plug is, and where flickering light comes from.

Next lessonCables and the line: connectors and the terminator