Illusory magic is one of the older forms of magic on Sable. The applications of entertainment-specific magics are a more recent development, especially the newer Audio Broadcasting and Holographic Recording fields. This area has crossover with certain aspects of comms and battle magic, as far as projecting sounds and co-ordinating the effects team for the former, and pyrotechnics with the latter are concerned.
Illusory magic is the ability to make things appear different to how they actually are, or to make something appear to exist when it does not. At basic level, you can co-ordinate one or two aspects of an image - say sight and sound, or sound and smell. Visual illusions have a habit of looking a little washed out, unless the mage concentrates hard on making the illusions appear solid. Audio illusions can be a little indistinct.
Illusory magic also allows pseudo-invisibility, at least to some degree - making something appear not to be there, rather than actually making it physically disappear. However, if the "invisible" thing or person moves, then the illusion covering them will become out of phase with its surroundings and it will become obvious that something is amiss. Also, at this level, the illusion is fairly two dimensional, and therefore from a different angle it becomes apparent that something is there.
Theatrical magics include setting up the basic lighting rig for a performance (positioning a light source to light in a certain direction, and with the right kind of hardness, and the ability to fade lights); setting up pyros and other special effects; and sound effects.
For the whole theatrical rig, each element would be a micro-spell, and the basic mage can only control so many elements at any given time. Therefore another part of the basic level of theatrical magic is the ability for a number of mages to work together in concert and remain in contact, although basic mages probably aren't good enough at working with others to gain a place in a full theatrical mage company.
Once you get beyond basic level, the rule of thumb for casting from scratch is that it will take thirty seconds for each sense you want to include in the illusion, plus a modifier of between zero and five minutes, depending on the area you want the illusion to cover.
And if you have a rough idea of what an illusion might want to be in advance, you can have programmed in the basics. For example, you might want to have half a dozen standard illusions in your repertoire - those you can have ready for whenver you want them.
Illusions can be refined to appear both more solid, and also to seem to have all the elements required to make the illusion convincing - sight, sound, smell, feel. However, a mage needs to at least leave some of his concentration on maintaining the spell, or it will gradually drift back to being less realistic.
Pseudo-invisibility becomes a little more useful, with the illusion acquiring three dimensional qualities and being able to change with the surroundings if the masked person/thing moves, given concentration on the part of the caster.
Disguise spells are a specific refinement of illusions, and first become available at partial specialisation. The duration of a disguise spell will vary, depending on both the strength of the caster, and how much effort he wishes to put into maintaining the spell. Here again, if he does not concentrate at least partially on the disguise, it will eventually begin to decay.
For theatrical magics, the basics are all built upon as the mage specialises. Mages become better at co-ordinating a number of elements, and keeping them running in the right place at the right time, or begin to link certain sequences of lights to specific sounds or frequencies. Also, mages at this level are better at co-ordinating with other mages to work in a team, even to the extent of triggering spells cast by other mages as long as they have been told the trigger, and will find it far more easy to become part of a professional theatrical magic effects team.
In addition, new and more complicated spells can be developed. For example, a "wires" spell (which allows an actor on stage to be pulled back as if "shot", or some other kind of involuntary motion) would first become available with partial specialisation, with the flexibility of the spell improving with experience and skill. Also, this would include a specific refinement of the telekinesis spells first learned with low level mech-tech magics - allowing for more accurate direction, and manipulation of light and sound become more specific and directable.
Sleight of hand magic also becomes available - the ability to make things appear to appear or disappear, or hide things under people's noses. However, it is possible for other people to spot what is going on, given sufficient time to study what is happening.
As with shields, at full specialisation, illusions and disguise spells can be left running virtually indefinitely without further input from the caster, although they will not stand up to dispel and null-field type magics.
Pseudo-invisibility becomes effectively as strong as the partially specialised combat magic equivalent.
Theatrical mages become sufficiently adept that they can control many and complex lighting and sound effects at once. In addition, their ability to co-ordinate other mages in a theatrical enterprise is much improved. Normally the directors of theatrical mage companies will have a full specialisation in the field, and will have the ability to take control of any spells built by their company.
Sleight of hand magic becomes less easy to spot.
For pyrotechnics, a basic knowledge of explosives and physics of explosions is needed so that pyrotechnics remain safe.
For lighting and sound an idea of three dimensional geometry is needed, so that sounds and lights seem to come from the right places.
This is a relatively new specialisation, which has taken the principles of the long-standing communications crystals (point-to-point communication by magical means), and adapted them for single to multi-point communication: effectively broadcasting. Development of this discipline has led to the first crystal broadcasting stations within the Kingdom of Sable.
A knowledge of the physics of sound, a better than average knowledge of the workings of recording crystals and a feel for how sound should fit together, as with sound engineering. Also, an in-depth knowledge of communications crystals.
Another new specialisation. This has actually developed from one of the forensic magic fields - the ability to pick up resonances from the scene of a crime and projecting them visibly. The basic techniques have been adapted to allow the recording of musical and theatrical performances, for example, and the placing of these recordings into crystals which can be replayed later. It is possible to edit such images, but this is a very delicate process.
A variant of this which is beginning to appear in the upmarket stores is a holographic catalogue system, by which holo-mages put images of big-ticket catalogue items, such as furniture, into cubes or crystals which can then be borrowed from the store, taken home, and the pieces considered in the setting the potential purchaser might want to put them in.
A knowledge of the physics of sound, light and movement, an artistic appreciation for composition and form, a better than average knowledge of the workings of recording crystals and a feel for how images should be edited together. Knowledge of the related forensic discipline is useful, but not essential
Under this specialisation mages can either mix sounds at a live performance, or make and work with a number of recorded sources, refining and smoothing sounds, mixing them, and actually producing recordings for crystals.
A knowledge of the physics of sound, a better than average knowledge of the workings of recording crystals and a feel for how sound should fit together. A feel for this field is most likely to be developed live - a sound engineer will only get better with experience, and experience here needs to be hands on.
A new variant of holographic engineering is 3D planning. This is becoming more common with companies and retail organisations which deal with fitting large-scale plant, equipment and furniture into a pre-designated space. It is becoming quite popular with furniture outlets, as it gives the customer the opportunity to see how potential purchases might look in their destinate room, and best be placed in-situ, without having to do a lot of physical rearranging.
Primarily, the main pre-requisite for 3D planning is good visual and spacial awareness.