You may wonder what the differences (apart from their appearances) are between Scanners and Moving Head fixtures, and why it is sometimes better to use one than another.

Scanners consists of a fixed optical train, often consisting of two motorised lenses, a couple of rotating colour wheels and gobo wheels and maybe a wheel of diffusion lenses to soften the beam. Some have extra features such as beam splitters and gobo rotators. The light source is found at the end of the scanner furthest away from the mirror. The mirror is positioned with two stepper motors, one each for movement in the horizontal and vertical planes. Scanners are very fast because they only need to move a small, lightweight mirror. The whole assembly is lightweight as it has no need to counterbalance forces due to rotation of a heavy head assembly and can fit into a smaller gap because all moving parts of the scanner are "contained" within the bounds of the scanner casing.

Moving heads, on the other hand, move the whole head assembly around, including the optical train. This produces some latency in the movement of the fixture as it has to compensate against the extra inertia of starting and stopping movement. The optical features of the moving heads are by-and-by the same as for the scanners. Moving heads are also heavier as the base acts as a giant counterweight to offset any sideways motion caused by the head rotating at speed. Moving heads have the advantage of a larger sweep range and look much more impressive than scanners when there are lots of them in the rig, all moving in synchronisation. They often (but not always) tend to be brighter as well, mainly because they have more room inside the bulb compartment than scanners allowing better cooling to be implemented.