Yes, Linnebachs are fun (but bulky) and yes, the tiniest
point source with no
reflector or
lens (a single, bright
LED is nice) will yield best imaging, but it sounds like you don't need that, and honestly the difference is negligible regardless for shadow making with people (more on that later). Use any source you have that's wide enough. I'd use that 50deg S4 happily -
flat field to minimize hot spot, shutters may be useful to control
spill outside your sheets.
The size of the source and its distance to the
screen determines how much travel your performer has between the two while staying reasonably in focus. This makes a tiny
point source ideal, but a run of the mill
stage fixture can work as long as you understand that the ratio of (distance from source to person/puppet/whatever casts the shadow) to (distance from person/puppet/whatever casts the shadow to
screen) determines how sharp an
image you'll get. Keeping the source to
screen distance constant, moving your performer closer to the
screen yields a sharper
image and also a more life-scale
image. Moving closer to the source makes the
image grow in size and lose sharpness.
Keeping that in mind, sharpness also has to do with the dimensionality of what's casting the shadows (if we're being picky, which it seems we don't need to be). Shadow puppets are usually
flat because, among other reasons, keeping all their details in the same plane allows them to all have the same degree of sharpness. Using people's bodies instead, you're going to compromise there, or in reality probably the way the dimensionality and movement of those bodies affects scale and focus will become an expressive part of the performance.
So, take whatever you've got to work with and spend a little time experimenting with placement for
image characteristics and minimizing hot spots (try to avoid showing anyone a direct
line of sight through the
screen to the lamp, and use the least transparent
screen material that works).
