Interesting optics thread

You weren’t talking about the LED when you said this, you were talking about a short throw projector:
“I think if you were building an ultra-short-throw video projector on the cheap, these could work great!”
A short throw projector needs to have an optical system that outputs light at a large exit angle, not collimate light from a light source with large incidence angles.

Also I see absolutely no retail digital projectors that use fresnel lenses on google, other than people that made a diy projector with an overhead projector and laptop screen.
And the only reason the image is even usable is because the light is going through a massive LCD that is 15” in size or something, not a regular projector LED which is usually less than one or two inches.

They must block such search results in Vancouver, otherwise you may attempt to rule the world…

Here’s some of dozens of YouTube videos:

And Instructables:

These guys tear down these Fresnel projectors:

Looks like Fresnels on both sides to me. My thought was to put the short focal range Fresnel on the front past the LCD.

I emphasize the phrase “video projector on the cheap.”

I’ve been around bowling for about 25 years. Back in the day they did not have computerized automatic scoring like they do now - automated scoring came about just before I started. What they did what give you a transparency with the score boxes and a yellow wax pencil. You set the transparency on the “Tele Scorer” which is basically an overhead Fresnel projector with a Fresnel underneath the table and overhead in a box with a mirror inside to face the projected image forward onto a screen.

OK, here’s a Fresnel lens designed to collimate 14 LEDs:

What performance would I expect from it?

  • cheap plastic fresnel = bad throw
  • lots of beam artefacts from LED cross-talk i.e. shining at the neighbouring lenses

OK, I don’t think this particular lens is good.
But I find the general concept of multi-LED aspheric VERY interesting.

But first one would need to solve the crosstalk issue.
It’s easiest to do with baffles. With a proper baffle system between the LEDs there would be no crosstalk whatsoever.
But what if the baffles were actually collars, carefully machined to have the right aperture shape?

One could build a multi-LED thrower (actually I wouldn’t prefer 14 except for huge lights. 3 would be more like it) with

  • high output
  • very high throw (collars!)
  • high efficiency
  • quite short focal length

Unlike multi-LED TIRs or reflectors (I’ll call them T/R) - these have no dead zones i.e. ones that don’t produce throw. However:

  • with fresnels reflection off ridges costs throw. And precision tends to be lower
  • with convex lenses - I strongly suspect the valleys between individual lenslets wouldn’t be very precisely made.

So the loss structure is different from T/R. It scales differently, f.e. 3-up is quite bad with T/R and should be good here. OTOH 7-up is quite good with T/R.

EDIT:
Again, I post here and within minutes stumble upon just the same kind of stuff. This time I got email with this:

You can buy adhesive backed vinyl with Fresnel patterns and metalized coatings behind; they use it for decorative stuff as well as cut for letterings and stuff with a prismatic effect. Which got me thinking… probably not practical, but one could do the opposite - take a Fresnel with a parabolic profile, put a reflective coating, and have a parabolic reflector that is essentially flat…

You can be an insect…

And buy the lens…

Sorry,
but this lenses are bullshit.

Ok for flood and many many Leds
but not worth to make a custom build with a lot of work…

The lens is good to protect from dust.
Another advantage I can not see.

Just my 2 cents !

Regards Xandre

I have seem those microlenses before. But macro? These are the only 2 that I’ve seen so far.

I’m not sure which lenses are you referring to? The multilens + collar concept or the microlens array?

Fenix E16 is known for its unique flat optics. This kind of optics is called RXI and quite popular in literature but nearly completely absent from the market. It seems to stifled by patents.

I found 2 makers that manufacture such optics. Neither looks like the Fenix one so there are surely more.

GR Optics has a family of COB lenses from 35 mm to 91 mm

Light Prescriptions Innovators makes a 41 mm lens:

Soraa uses RXI in their bulbs:
https://www.archlighting.com/technology/leds-understanding-optical-performance_o

Some paper that I liked, they fold light path RXI-style with refraction alone:

It’s the same as this, just worse.

And it’s called a catadioptric.

Oh, I forgot that lens. It seems to indeed use the same working principle. Except that Carclo has really low transmission, I suppose it spills light everywhere. That’s not the case with metallized reflector lenses.

The Fenix looks more like a hybrid reflector than a catadioptric. The hybrid reflector has a TIR that directs the light from the LED into the reflector. Polymer Optics makea then with aluminum reflector and plastic TIR. Auer in Germany makes them out of glass.

It doesn’t look so to me.
First, it seems to have a small metallized ring at the front that I can’t explain otherwise than “it directs light towards the main reflector”.

Second - it’s just too flat and angles don’t seem to add up. I think it would generate extremely wide beam with light hitting the side reflector directly. And we know that it actually collimates fine. Not neearly as well as a TIR in Olight S1 Mini but the output is nevertheless quite throwy.

Hard to tell from the pic, it could be just a reflection of the reflector surface too. But I don’t have access to one so I defer to the guys that do…

Fraen makes a cool optic for COBs; nested multi TIR which supposedly reduces spill. Would be great if they made them for COBs larger than 22mm.

I do have these cool hybrid reflectors from Auer, and aside from working well, are quite beautiful to look at in person:

The catadioptric is literally the same thing, a hybrid tir+reflector with a metallic coating on the rear side and the center which reflects the light coming at incidence angles too large for total internal reflection. That’s what allows the optic to be so flat.
Go look up the carclo 10158 on google and you will see it works in exactly the same way.
I own 4 of them.

I have a couple of the 10158 in my possession as well. They basically work like the old telephoto lenses for cameras - which were great because they gave you a lot of zoom in a more compact lighter package. But you needed either a good tripod or nerves of steel to keep your hands steady.

The hybrid reflectors from Auer, Polymer Optics, and Fraen each work in a somewhat different way. The Auer seems to be a combination reflector/side-emitting TIR, the Polymer Optics seems to be just a standard reflector with a typical TIR mounted on the center, and Fraen uses what they call a nested lens. I have a couple of the 110mm narrow spot Auer Jupiter reflectors as well, and they’re a work of art even more so than an optic. Have not obtained the Fraen nested TIR yet. I do have the Polymer Optics hybrid reflectors, but they are rather small, 30mm reflectors. I do plan on retrofitting them on some cheapie hosts to see how they perform.

The links agro posted, including that fenix flashlight, work on the exact same principle.
A metallic coated center reflects light that wouldn’t get reflected by TIR and the glass/plastic at larger angles TIRs the light back down into a reflective-coated surface to bounce it forward.

Yes I know that. I was merely pointing out that 1) there were more than one way to skin the proverbial cat, and 2) it didn’t seem obvious to me that Fenix does indeed have some kind of reflective coated ring pointed toward the LED. I can’t determine the depth of the reflector or the angles or such as Agro pointed out based on a head-on view or even the pics in Fenix’ website. I think it’s cool nonetheless.

Enderman, you probably know this, what does a smooth low angle TIR look like under an aspheric and catadioptric lens?

Your question is not very clear, but if I under stood it correctly you can’t put any kind of TIR under the 10158 catadioptric.
The 10158 has a small opening in the bottom that fits an LED, it is not like a lens where light goes through the whole thing.
Light enters it from a small hole and then it gets reflected/refracted forwards.

If you put the 10158 under an aspheric lens it will make a large ugly looking circle on the wall as the lens projects the front image of the 10158 which is hundreds of times bigger than an LED die.