If you can stand to hold your hand there for a couple of minutes, you should be able to use transparency film.) Trying to do that with an incandescent light source of any significant brightness will likely just melt the plastic (there are gobo holders designed to let you use transparency film even in, say, a 575 watt theatrical fixture, but they involve fan cooling and a special IR-reflective barrier placed before the transparency, and the transparencies still don't usually last more than a few dozen hours at most). (Try holding your hand a few feet from the lamp, and slowly bringing it closer until it either becomes uncomfortably warm or your hand is at the distance from the light source where the gobo would normally be. if you use an LED light source and the gobo is not practically on top of it, it's probably cool enough at the gobo position for you to print your own gobos onto transparency film. High resolution electronic dimming: 0 - 100. Electronic strobe effect with variable speed up to 20 Hz.
Hot-Spot: from flat field to 2,5:1 hot-spot. Frost: light 1° for instant softening of the projected gobo or framing shutters and medium 5° for even wash. You may be able to find one cheap at your local Goodwill or other thrift store. Iris: Motorized, stepless, pulse effects up to 3 Hz. a gobo is basically a single "slide", usually made of metal or tempered glass so it can withstand very bright/hot lights). Unless you're really into the DIY aspect for philosophical reasons, you're probably better off just buying a slide projector that already has a zoom lens, though (l8nite was correct.
By adjusting the relative positions of the lenses you can control the zoom (expansion) and focus. Basically what you need to do is construct a zoom lens by adding another (at least) two lenses, one convex and one concave, into the light path.
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