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Holographic Projection

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12K views 31 replies 12 participants last post by  mikeerdas 
#1 ·
Here's a technique I've used for several decades in a number of applications that I've never seen anyone talk about for Halloween but is a natural - holographic projection. It's possible, and fairly easy, to project full 3D solid-appearing full parallax images into space without any screens, fog, or anything. The trick is a large lens such as a Fresnel lens with a diameter as close to the focal length as you can get. I've used the lenses from the writing surface (NOT the projection lens) of old overhead projectors with great success. New plastic lenses about that size will run from $60 on up but junk burned out overheads can be had for free if you're lucky. Some old large-screen TV's used Fresnel lenses as screens and sometimes you can find a lens several feet across.

You want to find the focal length of the lens first. Put a flashlight or other point source of light far away (at least 30 feet) - I've used street lights outside - and focus the image of it onto a flat surface. Measure the distance from the lens to the image. That is approximately the focal length.

Now here is the trick. If you place an object at twice the focal length on one side of the lens, there will be a copy of everything the lens sees at twice the focal length hanging in free space on the other side, a full 3D solid object. The observer has to be facing the lens from that side because the projection exists only in the area framed by the width of the lens - the bigger the lens (or shorter the focal length) the better it works. Also, objects that give off light work the best, especially a single color as large Fresnel lenses tend to have chromatic aberration and multiple colors will result in some color fringing. Keep this in mind to stage you setup for best effect. Don't let people move too far off center as the object disappears as the projection moves off the edge of the lens.

This is a true holographic projection! If you project an incandescent light bulb the projection will feel hot! I have a clock that I made that projects the time 16" into space in front of it and if you place a tissue at the location of the projected digits they shine as if they were actually there. You can make a working (albeit clunky) virtual flashlight that way! The reason for this is that the lens actually recreates the wavefront of the source at the projected location within the limits of the angle of the lens and the viewer. That virtual flashlight actually shines a beam forward!

BIG BIG WARNING!!! IF YOU PROJECT THE SUN IT WILL INSTANTLY BURN WHATEVER IT TOUCHES AND INSTANTLY START FIRES!! The temperature of the projected sun can reach several thousand degrees!!! You can do welding with this setup! I've been able to burn text into the roadway writing with a 12 inch lens. Make sure your setup can't start a fire during the day. Be mindful that even if you cover the lens some materials are opaque to visible light but transparent to infrared and plastic lenses will still focus the heat even if covered!

The possibilities for Halloween displays are endless and the effect is amazing! It's very strange to see something hanging in the air, especially if it is moving, that you can put your hand through, and not have any kind of screen or smoke. With a large lens you can project an entire live person! I'll leave up to your imagination to decide what to project. I would love to hear or see photos of what you do.

ijv
 
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#3 ·
Great video! Looks like there are more videos to check out, too! Thanks.

The important things: big lens as close to f/1.0 as possible to get the widest viewing angle range and a good subject to project.

Plastic Fresnel lenses are not the highest quality so expect the image to be slightly blurred. That can be addressed to a great extent by having monochromatic point-source lighting to eliminate fringing and other lens issues and keeping the subject simple and small. The other important thing is to stage the display to keep the viewer within the best working range from side to side. It can be really dramatic to have the projection in front of any barriers to that the viewer can actually try to touch it. Very effective!

Remember to use a real solid object to project. A flat picture will be projected as a very thin flat image in space. I've used a small CRT this way and it's pretty weird to see an electric image just hanging there without any mechanism creating it, but solids look solid and very real if your lighting is good.

One thing I didn't mention before is that the two sides of most fresnel lenses are not the same. Projected on way the object is more accurate, but projected the other way it looks like it is stuck on the surface of a big bubble. Also, make sure you have a positive lens, not a negative one (like those stuck to the back of a van window to give a wide angle view). The negative ones won't work.

By the way, speaking of negative lenses, a few years back I made a helmet for a space suit with a negative lens as the faceplate and put a small UV light at the base shining up. If you used fluorescent makeup you could outline the features of someones face and when they wore the helmet people would see a tiny but very real cartoonish head inside that looked very, very alien! No one could figure out how this shrunken head could be so totally real! Of course, it was a real person but all that could be seen was the moving makeup reduced to a third its size.

ijv
 
#4 ·
Wow this has gotten my interest peaked! I have not heard of this. I just happen to have a big screen TV fresnel lens in my shed that I got out of a TV to use in just goofing around with. Melting pennies and catching fire to stuff, and it does do that very well. I was going to use it and make a solar cooker at some point.

I am going to have to do some tests with my lens in the next few days. I have to see what this looks like in person. If I can figure out how to make this work like in those videos....oh boy wait until next Halloween! (no way I have time for it this year, too many other projects right now)

Thanks for posting the info
 
#5 ·
Another thing - the projection image is upside down from the source object.

I wrote a couple of short papers detailing some of the formulas and geometry involved back in the '80's and might still have some stereoscopic pictures showing the effect I took from back then. If I can dig them up I'll post them to my website and post a link here.

At the time I was working on a camera for making 3D images using Integral Photography. The camera had to create a solid image in space of a scene which could then be captured on film covered with an array of pixel-sized lenslets cutting through the middle of the projection. The camera was huge - about as big as a desk - and had 16 inch diameter lenses. You could half climb inside to get a good view of the projection so you could position the film plane where you wanted it. Initial images were eerie, because they were pseudoscopic a person's face would appear dead still but would smoothly rotate in all directions to follow you around the room. I still have one hanging in my office. New visitors find it unnerving. I see them keep glancing at it but you can't escape it - the face is always turning and following you.
 
#8 ·
I'd love to give this a try. I've looked up replacement lenses for overhead projectors and found one for $15. The lens is 11" square and has a focal length of 14". So, does that mean it can only project 28"?

As I think I understand the set-up- point light shines at lens - object placed between point light and lens - projection of object occurs on otherside of lens - viewer must be on that side looking at projection/lens/point light.

Maybe I am confused? Please let me know.
 
#9 ·
I've had great success using those kinds of lenses. That's a great price - hopefully the quality is good enough for imaging. Make sure it's a lens and not a mirror! I've tried using some sheet magnifiers, too, but they tend to have a longer focal length compared to their size and the image quality is not so great, but they do work within their limits and they are cheap and easy to get to play around with, just not as stunning.

First, hold the lens flat with the surface facing you at arms length in front of you and move it around a bit. With one side of the lens facing you there will appear to be a virtual bulge coming out of the middle. this is actually the optical shape of the lens if it wasn't flat. That is probably not the side you will want to face the viewer because of the distortion it introduces.

Next, try looking at something bright like a window around 10 feet away or more. You'll see a small image of the window, upside down, located at about the focal length or so on your side of the lens! Because you have a lot of light around it might take a minute to notice that it is in space between you and the lens.
With the lens one way the virtual image will be floating on the surface of the blob you saw before, with the lens the other way it will be about the same location but the blob doesn't distort it or show up so much. That's the orientation you will probably want.

Here's the math: something located many focal lengths away will be projected upside down at the focal length distance on the other side of the lens. Something at twice the focal length will be projected at the same size as the original at twice the focal length on the other side. As you get closer than twice the focal length with the object, the projection goes farther away from the lens and the projection gets larger (very quickly!) on the other side until when the object is at the focal length, the projection is essentially at infinity and the effect falls apart.

Play with a flashlight in a dark room - set the flashlight where it shines at the lens. Stand on the other side. Depending on the location as just described, you'll see the flashlight bulb and beam reproduced at the location in front of the lens. If you move side to side it will work until the projected image moves off the edge of the lens, where it just disappears. This works really well with an LED light source like a red digit alarm clock. Because you want to keep the projection within the bounds of the lens, I've found that something the size of the digits on an alarm clock is about the best size for a lens from an overhead, it projects nicely at 1:1 and there is enough room for the viewer to move back and forth to nail the illusion. Play with it and you'll find what works best for you and what you are trying to do.

Depending on what it is you want to project, you can use the geometry to advantage, just remember that at twice the focal length on both sides you get a 1:1 reproduction and as you move away from that various distortions show up that ultimately mess up the illusion, with getting closer to the lens being more distorted than getting farther away. Play with it to get a feel for it.

Make sure you cover up the area from the lens out to behind the object you are projecting - any loose light is also projected and it tends to confuse the image you are trying to achieve. I've had best results with objects that give off their own light, although lighting an object can be made to work.

Let me know if you have more questions. Good luck. Waiting to here how it goes!

ijv
 
#10 ·
ijv,
Thank you for your detailed reply. I believe now I understand the concept. The only aspect I have reservations about is getting people to notice the effect from the sidewalk as they walk by.

I could build a black box for the object being projected. I then could light the object inside the box while aligning the lens with the object. Maybe that will filter out any unwanted ambient light. I imagine this to be part of our graveyard and would be one of the effects for visitors walking by at night. So, I could build a small ghostly doll, place it in the box, light it and blow a fan on it, project it and see what happens.


The lens in question is the writing surface of an overhead lens. That is the lens with the concentric circles. I'll report back in a few weeks if I can pull this together.

R
 
#13 ·
I've not seen that so I don't know. Back around 1989 or so I met with a person from Disney Imagineering and we talked about the possibilities of several optical technologies at the time including this one but I don't know if they used it - sounds about right, though a lenticular or barrier strip screen could also be used for glasses-free 3D. He knew about it and said that they had were playing with it at the time. They would need really big lenses as, from the viewers perspective, the projection only works as long as the projection is located with the lens as the background - the further out you project the less side to side range you have. If you had the money to spend on custom designed lenses (and they do!) there's a lot that could be done with this technique. With surplus overhead projector lenses you're typically looking at projecting things around 16 to 30 inches out, the further out the less angular range.

An overhead lens is about a foot on a side, a little bigger than a sheet of paper. If you put a sheet of paper on the floor and hold something 16" centered and up from it and look down, if that were the projection you could move your head back and forth as long as it is on the paper in the background. If you project it further out, if goes off the paper with less side to side movement of the viewer. Bigger lens, much more to work with. I had a large lens (about 4 feet on a side) that could project a head sized object out around 5 feet in front of it and have a comfortable amount of range to walk side to side to look at it. Had to keep it closed up because I was afraid that if sunlight hit it the house would burn down!

ijv
 
#14 ·
I am going to try this.

I pulled out my TV Fresnel lens and hung it in the garage with the center at eye level. The lens is rectangular but is 30" across at its narrowest point. Hanging it in the garage and going on the opposite side of the lens than the door opening I could see the bright outside area showing through the garage door. I held a piece of white poster board behind it and moved it forward and back until the image of the outside of the garage and the house next door came into focus. This distance was 30". I placed and centered an object 60" away from the lens (2x 30") then went to the other side and walked towards the lens until I could see the object. It definitely seemed to be in 3d space about 60" from the screen as far as I could tell. This was done in daylight and the image was not very good with too much light everywhere and all. I was just trying to see if I could see anything at all.

The only problem is it seemed like I had to be 3 times the distance (90") away when viewing to get the optimum effect. Walking closer made the object get big and distorted very quickly. Is that due to the focal length/ lens diameter ivy? How close to the projected image at 2x the distance should I expect to get before it blows up. Standing back you can see its in space a ways in from of you but you mentioned walking up and trying to touch it, I want that. LOL

I will work with it tonight when it gets a little darker and I will refine my setup to eliminate extra stuff all around the object and use a black backdrop. I think I will have much better luck with it. I will take pictures and video of what the result is and post them if they show the effect.

Oh and mikeerdas your question about the Disney Space Mountain effect. I have been to Space Mountain and I would say this is how they did it or something very similar. As I walk by the lens left to right the object seems to fly by in space. So substitute a asteroid model and it would look like they are whizzing by as you travel on the moving sidewalk you are on.

Ron
 
#16 ·
Ok tested it after it got dark. I did this quick and dirty just to see what the effect would be like. This would definitely not be the final setup if I did something like this for Halloween (next year) it really needs a good setup to guide the viewer into seeing it the right way.

I don't know how much it comes across in the video but there is a pronounced 3d floating out in space effect in person. I brought the wife out to see it and she said wow. Wow is good from her these days as I have been doing Halloween stuff so long its pretty much "oh another prop that's nice".

The video pretty much shows the setup. Some observations. There is a sweet spot to viewing the image as you go a couple feet or so in either direction the image goes out of view. If you move closer and to the side its easy to distort the image. A couple of notes on the lens I am using as it looks like the image has the potential to be a lot better. One the lens was very dirty being in the shed all year and second the lens is so big it wobbles and does not stay in a perfect plane, this results in focus or image distortions when you get near the un-viewable distances. Think a better frame would fix that and give me more viewing angles\distances. I don't think that would be an issue with a smaller lens.

Overall I was pretty impressed and could see the potential with the right setup. Would just have to figure out what to project, maybe the skull but a talking one? Too bad the projected item has to be upside down because that could limit the things you might want to project.

 
#17 ·
thanks for posting that.
that certainly explains alot.

as for the effect.
cant tell from the video... does it appear to float in front of the lens?
how far in front of the lens does it appear to be?
or
does it appear to float behind the lens?

so the skull is 60 inches behind the lens
and you are 90 inches in front of the lens
 
#18 ·
Its floating in front of the lens approximately 60", the same distance the object is behind the lens, its a little behind the white foreground object on the left. I tried to move the camera around a bit so you could see that it was close to the foreground object. I am filming about 90" in front of the lens.

It is real hard to tell in the video. Not sure how to film it to show the depth better. Especially since everything is so dark. It would help if the image was sharper and the camera didn't produce so much noise trying to shoot in low light.

Ron
 
#21 ·
Congratulations, Haunted Neurons, you've created your own space warp! Well, for light anyway - a copy of the light in one place recreated in another. Excellent demonstration! Now if only there was a good way to show off true 3D in video...

It sounds like you've got a good handle on things. Your math and geometry and your observations about the issues sound right. Any dirt on the lens is going to detract from the clarity but it also adds random glare and reduces contrast by bouncing light where it shouldn't be. Fresnel lenses aren't the best lenses for imaging to begin with but they are cheap compared to the alternatives. I've thought about casting a big lens out of plastic - even thought about freezing water in a satellite dish - but never have. (I once did win a bar bet in Wisconsin by betting I could start a fire with a bowl of water (I picked the bowl) - a few drinks later, it was around 25 below 0 that day, and I popped my ice lens out of the bowl and thanks to a cloudless sky and bright sun started a fire in seconds with my ice lens! I remember that adding something, I think it was salt, to the water made it clearer.)

Your use of the black background is good. Ultimately, you want to enclose the entire area from the lens to behind the object in flat black if you can. In addition to cloth, I've built boxes out of black foam core board which also works well and is very lightweight and sturdy.

Lighting - I've found that objects that give off their own light work best, especially if the light is monochromatic. Diffuse light tends to spread more. Fresnel lenses are net very well color corrected and different colors focus at slightly different distances. Red LED's work great, but even projecting that flashlight beam would work well. What's neat about projecting the flashlight beam is that the beam coming out of the projected image actually works! Something else that worked well was to use fluorescent paint with a black light. The light given off by the glowing dyes is pretty monochromatic and projects fairly clearly.

Placement - something at twice the focal length is projected 1:1 at twice the focal length in front. As you go away, the projection comes in close and closer to the focal length until at some distance several times the focal length it pretty much stays at the focal length distance. As you bring the object closer to the lens from twice the focal length the projection gets bigger and goes out away from the lens fairly quickly until the object is at the focal length where the projection is at infinity, but the illusion falls apart before that because of the distortion. You can compensate somewhat for that and project pretty far out by pre-distorting your model, but that can get complicated and the range of motion of the viewer is pretty limited. You just have to play with it until you are happy with the result.

It looks like you got it right in the video, but something else to check out - one side of the lens works better than the other side on the projection side.

Also remember that the projection can only be seen as long as it is backed by the lens from the viewpoint of the viewer. A line extended from your eye through the object must intersect with the lens or it doesn't show up. That is what limits your viewers range from side to side and up and down. This is true of all 3D technologies whether they involve glasses or lenticulars, or holograms.

Upside down is a problem with some objects, not so much with others. You can work around it a couple of ways. One is to put the lens on the ground or overhead so the object is now flat on the ground and the projection sticks up out of the ground or down from the ceiling. Both require a fair amount of space behind the lens (digging or a hole in the ceiling) but can be pretty spectacular. Another solution is to use a big mirror. You'll need a front surface mirror, not a regular one - the regular mirror will reflect double because there is a reflection from the front of the glass as well as the silver back. Big TV's that the lens came out of often have a big front surface mirror to fold the optical path so the TV isn't so big. Remember that you'll have a mirror image projected in case you have letters or something.

Looking forward to hearing and seeing more creative uses!

ijv
 
#22 ·
One more quick comment - any waviness or bending of the lens has a big impact on the projection. All that being said, a perfect solid projection would probably be disappointing for Halloween, it would be too real. A little bit of waviness or motion and a little spreading of the image gives it that eerie ghostly look like it's not supposed to be there. Too much, of course, just looks bad.

ijv
 
#24 ·
VinceMacPaul, I doubt that a 24" lcd monitor would have one. They were used mostly in larger projection TV boxes using CRT's or DLP's to direct the light of the screen to the viewer resulting in a brighter image, especially for CRT's. There were also some CRT based TV's that actually used a lens as a magnifier to make a larger screen than the CRT size. There are probably quite a few of those old junkers still around to scavenge if you can find them. The other big use was in overhead projectors. They were used as the writing surface to direct more light to the lens overhead. Those are typically about a foot on a side and have focal lengths around 14 inches. I've had a few of those lenses over the years to play with. A lot of old ones from schools and such have been junked as the bulbs burned out as cameras and video projectors have taken over their functions.

There are also some places where you can buy new or surplus lenses. Just a few years back a number of online shops were selling a 4-foot square lens as a solar collector for cooking or welding, don't know if those are still around though. Replacement lenses for overheads are available from a number of sources, do a search for "overhead projector repair" or "overhead projector replacement parts." Probably the same for the big lenses on some TV's like Haunted Neurons used.

There are several companies that make Fresnel lenses, Fresnel Technologies is one that I purchased parts from for a variety of projects around 20 years ago that looks like it's still around. They were very helpful on the phone back then. Edmund Scientific might be another - I remember they used to have a Fresnel lens section in their catalog. Look for a lens that has a diameter (or width) around the same size as the focal length. Smaller works but the viewing range side to side will be less even though they will project out more.

Most Fresnel lenses are made for directing light or magnifying, not 3D imaging so your results may vary. A really cheap and quick place to get one is an office supply store. They sell sheet magnifiers. They are just Fresnel lenses. The better ones work but are not as good as the rigid ones and tend to have a focal length that is longer than their width. They also do not project as clear an image or as far out. Still, for a few bucks it's something to play with to get a feel for how it all works and might be the perfect thing for a small display.

ijv
 
#25 ·
Thanks ijv for your continuing feedback. I've done some research now and understand a lot more about Fresnel lens and their commercial uses. You'll find us haunters a cheap lot and masters of salvage, haha. Thanks again for this wonderful idea. I've got a haunted hunch this tread you started might set a length record here.
 
#28 · (Edited)
Thanks ijv. Interesting that you got to discuss optics with Imagineering. I've always envied Disney's access to near infinite resources in achieving spectacular illusions--like having the World's Largest Pepper's Ghost Effect in the Haunted Mansion. There are viewing limitations with Pepper's Ghost. But they've got that licked with the Omnimover putting guests in the sweet spot. Also like the simplicity of many effects in the HM.

Congratulations Haunted Neurons, great job! And thanks for confirmation about Space Mountain.

There are three tweaks I've love to see for potential impact:

1) Setting your light source to fade in and out--like an apparition might. Or in the classic sideshow Girl-to-Gorilla transformation (or to Guy to Werewolf, etc).
2) Rotating the item being projected so it is, by turns, closer to and further from the viewer. Possibly with a slow RPM food rotator like the one I used for this el cheapo shadow effect:



Or having some conveyance where the object being projected just moves forward and backward on a horizontal plane to get that "comin' at ya" vibe.

3) Simultaneously combining items #1 and #2

I don't claim to understand all the optics here--they're probably beyond me. Need to re-read this thread and read it slowly. But I love (nearly) everything 3D. Started with a Stereo Realist film camera and graduated to a Fuji W1 digital camera with a damn cool autostereoscopic display built-in: 3D viewing with no glasses required. I know there are laptops out there with autosterescopic displays, but they probably aren't very big. Would be interesting for 3D Picture Frame-type set-ups. Like the Atmosfear FX Portraits effect DVD but in three dimensions.
 
#29 ·
...and don't forget when adding motion to move forward and back from the lens. That movement from the lens shooting out toward the viewer will get a reaction for sure. Linear movement of your object toward the lens will turn into exponential movement of the projection as it shoots toward the viewer while getting larger. Distortion won't matter much if the speed of the movement is right and with that big lens you could probably get it to jump out maybe 10 feet or more! Wouldn't have any side to side range but it would be over in a moment and you could go back to a 1:1 image again.

ijv
 
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