Coast flashlxights at Fry's Electronics put Fresnel Optics in the main stream.

Fry’s is a large electronics store originally in Santa Clara and with at least one other store in Palo Alto. It is the other place I know of in the San Francisco Bay Area, besides Illumination Supply, with a good selection of flashlights, and at least locally, it must do much more business. Today I saw a separate display of Coast lights at the end of an aisle, in addition to their dominating the flashlight aisle. They ranged from 1xAAA size to a 4xD cell light priced at about $185. Most of them have LED Lenser type optics.
So Fresnel lenses with both reflecting and refracting elements are now main stream for flashlights, in spite of the forums and the lack of other optical designs in production.

when you were talking about lenses in general in my other thread?

you are familiar and knowledgeable about them… its not everyone that casually drops talking about achromats, and knows they are convex and concave affixed together…

the knowledgeable lens talk? really INTRIGUES me when you talk about the other stuff i never heard of…

the “stage lighting” lenses, and multiple fresnels.

in my mind, i picture “multiple fresnel” being two, circular, “circles cut out of a page-magnifier” sort of affair… now you are talking about reflecting AND refracting fresnel components…

…and i am getting curious as HECK to see some of them with descriptions, i aint never SEEN stage lights up close, nor can picture reflecting fresnels… i just dont have a frame of reference to go on to imagine the setup…

write about it, man! sounds like “bleeding edge” stuff… i’m sure i aint the only one here curious about it all… right?

OOoooohhhhHHHHhh sounds interesting!!! I wanna know MOARR

Look at the Wikipedia article on Fresnel lenses. Fresnel lens - Wikipedia I haven’t read it all yet, but it is good. Because it shows lighthouse lenses, I am now calling lenses with both reflecting (TIR or silvered) and refracting (like an aspheric) elements, such as LED Lenser, Fresnel lenses, even though in the past I have seen that term used to describe lenses with only refracting elements. I have seen two “first order” Fresnel lighthouse lenses, the one at Point Reyes and the one at Pigeon Point. These are peak 19th Century technology and very impressive, but scaled down the shapes could be molded. Historically, in the US, silvered reflectors were used until the Lighthouse Comity acquired these lenses from Fresnel’s company in France, so I expect the same progression in flashlights.
I do have design experience, long ago, with a sort of optics. That was the optics of charged particles moving through magnetic fields. That is basically geometric optics, like flashlight optics, but different in detail. I also have extensive general knowledge of electromagnetic fields.

One way to design a new Fresnel lens for a flashlight would be to scale down a lighthouse shape.
For an original design, one needs a geometric optics optimization.
In either case, there has to be a precise way to machine and polish the mold that will be used in production. The surface must be smooth to a small fraction of a wave length of light. It probably isn’t practical to produce lenses by NC machining, like flashlight bodies, because glass is hard to machine and plexiglass melts if it is cut too fast. The tooling and production processes must be quite similar to those of aspherics.

The process of optimizing a new design is straight forward and should not deter anyone with the capability to put the design in production and market it. All the physics that is needed is given by geometric optics. Geometrical optics - Wikipedia The only thing needed from wave optics is that the segments shouldn’t be smaller than maybe a tenth of a millimeter, even if the shape is very accurate. The equations needed are simple and explained in detail in Wikipedia. Snell’s law Snell's law - Wikipedia describes the focusing of lenses. The law of specular reflection describes that of mirrors. Specular reflection - Wikipedia In addition there is a minimum incidence angle for total internal reflection (TIR) Total internal reflection - Wikipedia . For angles less than this, the surface must be silvered. The light lost by reflecting from a refractive surface is significant but doesn’t really need to be considered.

It is possible, with these equations, to design the lens by hand, as Fresnel did, but it is much easier to write a simple optimization computer program. One source of optimization algorithms is Numerical Recipes. Numerical Recipes - Wikipedia , http://www.amazon.com/s/ref=nb_sb_ss_c_0_17?url=search-alias%3Dstripbooks&field-keywords=numerical+recipes&sprefix=Numerical+Recipes%2Caps%2C1135 . The requirements of geometry, performance and what ever else, have to be combined and quantified in a figure of merit that is a function of the input and output of the geometric optics calculation. The program then minimizes or maximizes the figure. One looks at the result and changes the formula for the figure until the result is as desired.

This must be the outline of what the Two Brothers did to design the LED Lenser, but it seems that having only two elements makes it more difficult because they should not interfere with each other but their shapes depend on the optics. With several small elements, the overall shape is more independent of the optics. You can see that in some lighthouse lenses that have conical tops and cylindrical bottoms.
Though it is not clear, it appears that Coast and Pop Lite have licensed the Lenser design. The coast HP1 is a little different in that it is optimized for flood instead of throw, but once the optimizing program is written and one design is found it wouldn’t be hard to re-optimize a variation of it.

Fry’s has been carrying Coast LED Lenser flashlights for at least 10 years.

Coast was originally LED Lenser’s US distributor and both names were on the box. Several years ago LED Lenser eventually went its separate way and Coast started marketing its own flashlights with the same style of optics.

The main advantage of this optic compared to a typical budget aspheric lens is that the optic wraps completely around the LED in both flood and spot mode. The result is no light is wasted. In a ceiling bounce test an LED Lenser produces roughly the same total lumens in flood and spot.

In contrast, a typical budget aspheric light has a flat lens bottom that doesn’t wrap around the LED. When the bezel is extended to spot mode much of the light from the LED hits the inside of the bezel instead of the lens. This can result in 50% or more of the total lumens being lost.

FYI: I don’t know if they still do, but REI also in Silicon Valley used to carry LED Lensers. I purchased a zoomable rechargeable one powered by a 14500 cell approximately 8 years ago there.

Fritz,

You may be trying to invent something that's already been invented.

That's a Surefire Invictus. It combines a TIR and an internal lens, and the internal lens is a Fresnel.

The design is similar to a LED Lenser optic, combining a TIR with an internal "thrower" lens. Obvious differences are that the Surefire optic does not zoom out and the LED Lenser optic does not contain a Fresnel.

Selfbuilt reviewed the Invictus and has beamshots. www.flashlightreviews.ca/UB3T.htm

I think one thing should be clarified.

The “lighthouse” style fresnel lens isn’t inherently better than what LED Lensers already use.

The lighthouse lens is comprised of the following:

  • Inner fresnel style segments which refract (bend) the light that passes through them. These segments create the effect of a large aspheric lens, but are much thinner. This is the part that is ordinarily thought of as a “fresnel lens”.
  • Outer TIR segments which reflect rather than refract the light that passes through them. Light enters these segments and is reflected off the back edge and out the front of the light.

The Main advantage of the inner fresnel segments is that they allow for a much thinner lens. Instead a of a bulbous aspheric lens, you get a similar effect without the thickness. The disadvantage is that at each transition (edge), you lose some light. As a result, a fresnel lens is less efficient and will produce less throw than the same width and focal length aspheric lens.

The main advantage of the side TIR segment in an LED Lenser is that they wrap around the emitter. Light emitted out the side of the LED that would normally be wasted into the side of the bezel in spot mode instead enters the TIR and is reflected out the front of the light.

Since the center aspheric lens in an LED Lenser style optic is so small, there’s very little to be gained by converting that portion to a fresnel lens. You’d lose throw without noticeable decreasing the size of the lens.

So it was already in the main stream. But we still need new budget designs. I don’t think the zooming is a problem for the optics. The TIR part stops catching light.

I don’t know if that lens really has more than two segments. The rings look like they could be like orange peal on a reflector.

Yes, my main complaint against the Lenser lens is just that it isn’t more widely available. More segments save space and allows more design freedom., but I don’t think they missed much by only using one TIR and one aspheric. Maybe they thought it looked better that way and maybe it does.

Romisen RC-39:

And:

http://www.ledengin.com/products/lenses
LZ4-Series TIR lenses
Beam Angle (°): 7.4, 14, 18, 22, 40, 8 - 45 zoom

I got some Carclo optics to look at. The “TIR” optics I have seen has a cylinder or cone hollowed out above the LED. Its main purpose seems to be to refract light onto the TIR surface. This is a wide cone in the Lensers and narrow in the others. There are various treatments to the top of this tunnel. Some, including the Carclo pieces have a converging lens on top of the tunnel, making them two zone focusing optical systems, like those mentioned above.
Most of the Carclo pieces have a flat top, unlike the Lenser designs that have a diverging cone and a convex lens on top. The flat topped ones have the convex lens surface facing downward toward the LED.

Others, that seem to columnate better have the convex surface in front, like an aspheric zoomy or LED Lenser optics.

Provided the LED were mounted on a small pillar, the lens topped ones would seem to work well in zoomies. The flat topped ones would behave like an aspheric with the lens upside down. Trying that quickly, I get wide flood with the lens almost touching the dome but an uneven pattern at intermediate distances.

One issue with those Carclos is I assume they aren’t designed from the ground up with a zoomie in mind. As such, the pocket in the bottom probably isn’t deep enough to allow an LED to extend into it mounted on on anything but a flat star. What makes an LED Lenser zoomie so effective is that the optic surrounds the LED in both zoom and spot positions. This is different from a conventional aspheric where the back of the lens is flat and in spot mode much of the light is wasted into the sides of the bezel.

However, in order to make this work, most LED Lensers require the LED to be mounted on a pillar. The optic then surrounds this pillar in flood mode. Usually a flat star won’t work.

However, I did figure out how to make a simple, but effective pillar that can be mounted on any Noctigon star.

To make the pillar:

  • Cut 4 pieces of sheet copper into small rectangles all roughly the same size.
  • Laminate 2 of them together into a sandwich with solder or solder paste.
  • Apply a thin layer of arctic alumina to the top and bottom of the laminate. This layer should be thick enough to completely insulate the top and bottom. On my sample, I also added a layer of Kapton tape, for extra insulation, but I think it’s not necessary. The tape didn’t hold when it got hot, while the arctic alumina would. If necessary lightly file the top of the arctic alumina after it cures so it is flat.
  • Then using more arctic alumina glue the remaining two copper rectangle on the top and bottom of the sandwich. You should end up with all 4 layers of copper stacked on top of each other, with a gap of arctic alumina between the two outer pieces and the two inner ones soldered together. This is now your pillar.
  • Optional: Test with a DMM to make sure all 3 copper sections of the pillar are electrically insulated from each other.
  • Rotate the pillar onto its side so the edges of the copper sheet touch the bondpads on the star and the LED. The goal is to solder your new pillar onto the Noctigon’s bondpads and then mount the LED on top.
  • Before final soldering, File the sandwich to fit. It should be exactly as wide as bondpads on the star, and you can file it to whatever height you want so that it sits at the right height. Also make sure the top and bottom are close to flat.
  • For final soldering, apply solder paste, then mount the pillar onto the star and the LED onto the pillar. Reflow the entire package at the same time. On mine, because I used Kapton tape, my pillar would fall to pieces when it got hot, so I used a tweezers to hold it vertical during reflow. If you skip the Kapton tape this shouldn’t be necessary and it should be just as easy as a typical LED reflow.

Electricity and heat are conducted right through the pillar so you don’t need to worry about trying to mount bondwires. And because the pillar is copper and mounted on a copper noctigon heat conduction is excellent. Also, another benefit of this pillar design is it will fit in any LED Lenser optic’s pocket because the pillar is no wider than the LED itself. You can use this technique to build the pillar to allow an LED lenser style optic to work in any zoomie.

If you want a cheap source of LED Lenser style zoom optics, check out Orchard Supply Hardware (OSH). I was there a few weeks ago and noticed they had several different cheapie clones with that optic type all in the $8-$25 range.

The hole in the Carclo optics is much smaller than in the Lenser, so it would take a very small pillar.
What I saw at Orchard Supply was Coast lights. Most of them are not cheap. The HP1 can be gotten cheaply but it has wide flood and not a full spot mode.