Interesting optics thread

There are many optics that are interesting for some reason but neither fit any existing topic nor are worth having their own one.
Let’s discuss them here….

Knight Optical has a family of extremely strong Fresnel lenses, F# = 0.2.
15 mm lens needs to be just 3 mm above the die to focus on it.

This leads to very high light collection - 82% of all light gets captured to the beam.

They are available in many sizes from 15 mm to 125 mm.

High collection is close to high efficiency but is not all of it. The lenses are not AR coated stock (but manufacturer offers such option). They’ll suffer pretty high reflections at the peripherials unless coated.

Will they throw?

1. Fresnels suffer from reflections off the peaks, that reduces throw
2. Strong lenses are worse collimators than weaker ones
3. Fresnels have larger clear aperture than regular lenses of the same diameter - giving them natural 23% throw advantage over a standard aspheric
4. These are “precision” grade items

So….I have no idea if they throw but I wouldn’t expect them to have record-breaking potential.

But they have other advantages:

  • super short zooming movement makes head design easier
  • little effort to adjust focus
  • head can be very compact
  • the lenses are very lightweight

So…interesing base for a small, light and efficient zoomie. :slight_smile:

ADDED: NTKJ has a similar line, from 15 to 250 mm:

At 50+ mm they offer even higher pitch. And they have negative lenses of the same strength as well (but only 25, 50, 100mm).

They make TIR lenses for things like emergency lighting that puts out a square beam aand they have them with different beam angles as well. Don’t know what it’s called but I know Polymer Optics in UK is one company that makes them.

Speaking of interesting optics they have a few, from hybrid TIR/reflectors, 3-up color-mixing lenses, some crazy Fresnel lenses for IR detection…

I built a version of Enderman’s Light Cannon with a Fresnel (thread in the Spotlight section). Similar to Light Cannon and OptoFire, the light source moves - in effect creating a zoomie. It’s actually pretty cool going from pencil beam to column of light 4” in diameter. I might print GOBOs to flash onto walls like the moving head beam projectors. I’ve even considered making cheap moving head projectors with Fresnel lenses, the light weight would need just small NEMA14 steppers…

Interesting that this conversation came up. I have this Acrylite diffusion lens arriving today (52mm), which will fit my Maglite.

Heard about it on another forum, just wanted to see how well it works.

Thanks for starting this thread. The LEDiL Seanna doesn’t fit anywhere well. Even fewer people have tried them. And they aren’t particularly practical. Not even sure who they made these for. I tried with and then without the inner lens (12ft) to see the difference in this Osram white flat 1mm^2 build. Without the inner lens it might have more cd but produces some strange colors. The last picture is with only the inner lens and no Fresnel. The ring is about 12 feet across and around 8 feet away.

I thought about this too. Methinks the TIR is made to collect the LED light from the outer beam angles, with the Fresnel taking care of the front of the beam? I’m not sure if the Seanna was even intended for LEDs like a White Flat, and I did notice those rings in the fully assembled light. But when I held the MCPCB against the installation “plane” I didn’t recall seeing those rings, at least that pronounced, so I think perhaps the White Flat is not in the optimal position vertically?

Thanks for the reply. I tend to agree with you. The similar Black Flat is in their documentation. I reached out to Ledil about MCPCB and they sent me some info. Some of which I posted in this thread. Not much use for me, but its nice to see they would try to help. I like to play around with some different gaskets but there is not much out there yet for this LED. I wish I had way to calculate cd/lm to know if I’m close. That efficiency number is quite high.
Page 4 of the spec sheet.
LED OSLON Black Flat
FWHM 1.2°
Efficiency 94 %
Peak intensity 1196.000 cd/lm
LEDs/each optic 1
Light colour White

Interesting optics.

I’m not sure a 15mm fresnel lens with 3mm focal length would be that useful though.

I experimented with fresnel zoomies a few years ago. I had a combination of cheap fresnel lenses (about $8 each) and more expensive ones (around $30 each). My impressions:

  • A short focal length doesn’t increase throw at all …. all it does is give you a wider hotspot. to increase throw you need a wider or better quality lens.
  • The default cheap plastic aspheric lens that comes with an $8 zoomie easily outthrew both fresnel lenses by a significant margin.
  • Both fresnel lenses were able to produce wider flood beams than with the stock aspheric lens
  • Due to light scatter off the peaks of the fresnel lens the area outside of the beam tended to be softly lit, compared to pitch dark with the aspheric lens.
  • The cheap fresnel lens (I forget where I got it) had a longer focal length and didn’t throw as well as the more expensive one from Edmund Optics. The cheap one produced a fuzzy square in spot mode. The more expensive one produced an actual image of the die… not as sharp as with the stock aspheric lens however.

So based on my experience this is what I would expect of the 15mm fresnel with 3mm focal length:

  • Very wide hotspot (image of the LED surface)… almost as wide as the beam in full flood mode.
  • Flood mode would probably be relatively narrow. The problem is the focal length is just too short. For practical purposes you need to leave at least a 1mm gap between the back of the lens and the top of the emitter dome… that’s already 1/3 of the focal length used up. Then there is the height of the dome itself. Even for an XPL HI or Black Flat with a flat dome that’s probably another 1 mm.
  • Throw (intensity of the brightest point in the hotspot in throw mode), would be worse than a cheap 15mm aspheric lens that costs less than $1.
  • Overall this lens probably wouldn’t make for a very good zoomie, with its narrow flood, minimal distinction between the spot and flood beam, and inferior throw.

I think if you were building an ultra-short-throw video projector on the cheap, these could work great!

Those would work horrible, as the fresnel ridges would completely distort any image projected through it.
Projectors require precision grade single surface glass lenses.

Yes, for 720p I agree. For cheapie 480p LCD projector, it probably doesn’t matter. The final lens yes should be glass but in back of the LCD can be Fresnel (to collimate the light from the LED), and in fact with the cheap Amazon projectors the lens in front of the LCD is also Fresnel.

Sure I can go to Edmund or ThorFire and get some precision ground lenses… but this is Budget Light Forum, not “the sky’s the limit budget” LOLOL! I emphasize “on the cheap” here. Sure it’s cheaper to just buy a crap DLP projector off eBay and put a brighter LED, but that’s not a build - that’s an installation job. That’s no fun.

Just thought I’d put up this oldie but goodie optic for nostagia sake, from Inova TIROS series. It had a really great narrow throw with just a little spill.

Regrettably I had to send my light in for repair for a cracked bezel lens and rather than replace the lens they replaced my entire light but with a newer reflector based model :frowning: Had I known they would not return my light I would have simply replaced the cracked lens myself. I miss that beam.

First of all, projectors do not collimate light.
Otherwise the image would be a few centimeters in size.
The entire point of a projector is to do the opposite, and project a large image not a small one.

Second, even 480p would be completely distorted.
No matter what resolution you use it would be completely messed up not only due to chromatic aberration but also because the ridges of a fresnel lens are not perfectly aspherical.

Imagine your projector has a resolution of 1 pixel, it would still look like crap.
You can see this by looking at the die image of fresnel throwers, it doesn’t even look like a square anymore.

Thanks a lot for sharing your thoughts and experiences!

Some of this could be improved, f.e.:

  • these lenses have smaller groves than Edmunds which hints at higher quality - but that’s not warranted
  • using a lens much larger than 15 mm makes any necessary gaps less significant
  • using a LED that has extremely thin silicone layer may do the same (White Flat?)

So I really don’t think that in a well done light the flood would have width close to throw.

Also now I noticed that such light could put more lumens in the beam than any optics other than TIR.

But seeing your results I’m really not convinced it’s worth trying.

Interesting…is it glass? What’s the size?

This is from Can Fang’s (4sevens) very recommendable synopsis: LED optics in flashlights

Because the LCD screen will only allow light to pass through perpendicular to its plane the light has to be collimated to allow this. AFTER the light has left the LCD it is then focused on the projecting lens. You can argue about distortion all you want and are 100% right. But they’ve been making cheap projectors like this now for at least a decade. They’ve been using Fresnels in overhead projectors for decades.

As to Fresnel throwers… You can see in my pics I project an almost perfectly square die image - 200 yards into a brick wall. It’s rectangular now because I put a 2mm^2 in. I can’t capture it with my cell phone but at 40ft focused i could read the inscription on the MCPCB at 40ft. Possibly because the RLT moved on me and is illuminating the whole MCPCB.

So sure, I don’t expect a hi-def video projection. But you can search the thousands of YouTube videos of both DIY and cheap manufactued video projectors and see the image quality, while not great, is far better than you describe.

If I recall correctly, it was made of Polycarbonate. The diameter of the optic from that light was about 1-inch at the widest point.

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.