Looking for a lense that will "straighten" light

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.

I have been told that I need a Fresnel_lens or a Fresnel_lantern to help to “straighten” the light though the stencil.

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.

My questions are:

  1. How do I calculate the distances the 4 different Items need to be apart from each other?
  2. Where can I find cheap or free sources of Fresnel lens? Do you have any that you can give me?
  3. Is a Fresnel lens what I am looking for or should I be using something else?
  4. Do you have any other suggestions for me or links to similar projects?
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You my want to consider a head light lens or a complete head light assembly. These are designed to straight light.

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:
image

https://www.google.ca/webhp?sourceid=chrome-instant&rlz=1C1AVSX_enCA585CA585&ion=1&espv=2&ie=UTF-8#q=making%20a%20parabolic%20reflector

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.

Yes the stencil on the overhead projector will be the easiest and best way.

Just skimming through this, what about using a Mag-lite flash light? You can focus the beam with those.

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:

http://mindofasnail.tumblr.com/

Argh. I saw a free overhead on craigslist about a month ago but silly me thought no one would have a use for it. Next time I will grab it.

Lee Valley also has a “projectors scopes”
http://www.leevalley.com/en/gifts/page.aspx?p=44193&cat=4,104,53208,44193

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?

I will look into that today, Thanks [quote=“Jarrett, post:5, topic:313”]
I would recommend a parabolic mirror instead
[/quote]

Sounds good, Same thing @tdwebste said.

So far I have not found any intact overhead projectors. This would definitely make the most sense.

Basicly thats what I am using right now and it produces a blurry silhouette

I need to find some working overhead projectors.

I will try this,

Having the stencil external and visible is not a requirement of this project.


Thanks everyone I will update this post with my results as this project progresses.

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These guys took apart an overhead projector for their project. No build instructions but their results look pretty cool.

http://www.ratchetup.com/sitespecific_media/2008/05/street-lamp-ste.html

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How is your project coming? I’m interested in this because I want to project some of my papercuts too.

I came across this setup
image

Check out the project at

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.

It didn’t work to great straighten out the light.

I have been told that I should actually use a single point halogen light instead. Thats what is used in this project http://www.cubebreaker.com/laser-cut-cube-shadow-art/

I didn’t get a chance to try out any of the other ideas in this thread. Thank for your advice everyone.

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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.

Also see http://www.edmundoptics.com, look at their app notes and such.

I also have a binder of their vintage manuals, great source of knowledge about projection et al. I’ll try to dig that out…

SDY

Don’t try to straighten light. It was born that way. Learn to love it for who it is.

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There are projectors at Ikea that would work. They are in the kids section. Just noticed the other day.

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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.

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