Here are a couple of foci I developed that should make any conjurer's life a little easier.
Watcher Focus
Cost: 1,500 Nuyen Binding: 2 Karma
Summoning a watcher spirit is one of the most tasks any conjurer can perform, they are easy to summon and very useful. However, summoning one for an extending period of time can be quite difficult, not to mention taxing. A watcher focus gets around this. When you activate a watcher focus and summon a watcher spirit, the spirit will continue to exist and serve you in the astral plane as long as the focus remains active. If the focus is deactivated for any reason, however, the watcher is immediately banished, regardless of how much time it may or may have had left. Only one watcher may be sustained by this focus as any given time. The magician can end this effect at any time as a free action, after which the watcher is banished.
Twilight Focus
Cost: Forcex2,000 Nuyen Binding: Forcex2 Karma
A logical extension of the watcher focus above, the twlight focus allows a magician to partially circumvent the restrictions placed on summoned spirits without having to resort to expensive(and draining) binding rituals. A magician can choose to sustain a spirit she has summoned(but not bound) into the focus. The spirits force must not be greater than the force of the focus, and only one spirit may be sustained by a single twilight focus at a time. As long as the spirit continues to be sustained by the focus, the spirit remains conjured into the astral realm, and will not depart to the metaplanes until they run out of services. When sunrise or sunset passes, the spirit does not depart as per normal, but the services owed by the spirit is reduced by one. The magician can end this sustaining effect at any time as a free action. If the sustaining effect is ended for any reason, or the spirit runs out of services, the spirit immediately departs to the metaplanes. You may still only have one unbound spirit summoned at a time, so having multiple twilight foci is rather rendundant.