I am making a project that requires me to make crisp shadows using light through a stencil. The light source a directional 100W LED combined with a paper stencil. The light goes through the stencil and is projects a shadow on the wall behind it.
This first image shows the light coming through the stencil and making a nice crisp silhouette on the wall.
In the second image the stencil is closer to the light source and farther away from the wall. The silhouette on the wall behind is blurry and not what I am looking for.
Retail fresnel lenses are prohibitively expensive costing in the $100s. I have been told that I can probably use lenses from overhead projectors or projection TVs and maybe even a projector. I am still looking for some free or cheap fresnel lenses
The diagram below shows my plan for the set up. I can control the distance between the light source #1, The lense #2 and the stencil #3. All three components (#1-#3) should fit within a 3 foot box. The distance from the stencil to the wall maybe anywhere from 8 feet to 40 feet.
This can be done in two ways. The first is to put a lens between the stencil and the wall so you can put the stencil in focus on the wall. The second way is to turn your light source into a point source of light using a reflector and an aperture. The first way tends to work better (overhead projector) or both methods at once can be employed.
Oh, also, you can get small Fresnel lenses at lee valley tools. They are credit card sized and are plastic. There may be a third method by putting the light into focus on the silhouette... I don't know if this will work.
Good quality lenses tend to be very expensive. I have some of those credit-card fresnel lenses, but I don’t believe they are actually fresnel, and they are literal garbage that are designed for people with poor eyesight to read books easier and nothing else.
I would recommend a parabolic mirror instead. I leave you with the following pieces of information:
edit:
if you can find one of those overhead projectors, just dropping your stencil on top will still be the easiest and best way to accomplish what you want. Ask around at elementary/high schools, I bet they have a bunch in storage just rotting away.
There’s a really cool fringe fest show we saw a few weeks ago (in a pre-fringe screening, they might still be showing it) called Caws and Effect. It was all done with two overhead projectors and lots of cool cutouts, one of the nicest shows I’ve been at. Definitely worth checking out:
I think that using a light source which looks more like a point source will also give you better results.
The incandescent bulb isn’t really a point source. Your blurry lines are from getting shadws from the top an bottom of the bulb.
Using a single white LED, or other physically small light source should work better, perhaps even putting a piece of cardboard with a small hole in it betweem the incandescent bulb and the stencil.
FWIW, in theatrical lighting, "gobo"s put the stencil between the light source and lens, instead of in front. should make lens selction significantly easier.
You can also think of this as how slide projectors worked. (bulb)-> (slide) → (lens) → (screen).
Is having the stencil external and visible part of the look you’re going for here?
My project has changed a little bit and I don’t need to cast shadows out of a center point any more. I did do some more research for anyone else that needs to cast large shadows.
I got a Fresnel lense from @SDY and decided to try it out.
Hmmm… If you look at a retroprojector, it appears to go like this: light source, some distance, Fresnel lens, pattern to project, some more distance, LENSE(S), plenty of distance, target screen.
But it’s so divergent and flighty. You can’t get it to sit in one place for any amount of time… hmm… Light must be the epitomy of ADHD. It even hyper-focuses at times.
