Rarity: Very Rare (30', 60'), Legendary (90', 120'), Legendary+ (unlimited)
This item takes the form of any class-specific spellcasting focus.
When a spell is cast with this focus present (not necessarily used as a component), the caster can choose to make any effects that are "stationary" be stationary with respect to this particular focus (id est, the "stationary" effect follows the focus). When used this way, the focus must be within the effect. If the range of the spell is "Self", it becomes "Touch" when this effect is used (and the focus must be touched or held).
The casting time, duration, spell slot, and use of concentration cost is unaffected. The effect continues as long as the focus remains within either the range of the focus or the spell's range (treating "Touch" and "Self" as 0'), whichever is greater. If this range is exceeded, the spell ends. The spell can also end in any way it originally could.
If the movement of the spell effect creates an untenable or impossible situation (at the DM's discretion), such as two colliding moving walls of force, or trying to crush a creature against a wall using a boundary against which it cannot move, the spell ends. (The DM may decide on other sensible resolutions, however, such as applying a reaction force to the focus itself.)
Such foci can be created by vectomancers (space wizards) using a ritual they often keep away from outsiders (especially those disgusting chronomancer heathens). Though not frequently discussed, rumor has it that the ritual involves the expenditure of no less than three 9th-level spell slots. Yet more 9th-level spell slots--and a finer material focus--seem to give better ranges. The "unlimited range" one has yet to be created by mortals.
The focus retains its usual AC and HP. When destroyed, any spell it is supporting ends.
Per Detect Magic, the focus has an aura of no particular school affiliation.