# Aspheric lens tricks?



## gcbryan (May 5, 2010)

Has anyone experimented with "cleaning up" the beam when using aspheric lens? It's probably less of a problem with dive lights than with non-dive lights with aspherics (due to underwater condition) but I'm curious.

Aspherics available to us are generally rather cheap lens and commonly have artifacts. I've used translucent Scotch "Magic" tape on the back of the lens and left the center portion clear and this cleans things up nicely without effecting the portion that is "throwing". It does cut down on the light in the surrounding area and it would be nice to not have to do this but with really ugly beams it's well worth it.

I'm wondering if anyone has tried hairspray to selectively control diffusion on any lens even including flat glass lens when using a reflector.

With a reflector the beam is difficult to pin down as spill is coming from the center and hotspot is coming from the edges. It seems that it would be possible however to diffuse the center (spill area to improve beam quality) and to diffuse the very outer edge of the hotspot (difficult to pin down location however) to blend it into the spill.

Has anyone experimented with anything like this?


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## Packhorse (May 5, 2010)

This is probably a topic best put under the custom build and mod forum than the dive light forum as its a generic light question and not one that applies only to dive lights.
You will get many more people reading and replying to it with their experiences.

I have not tried doing it myself. I think the best way to get a clean beam is to use a higher quality aspheric.Different LEDs will also change beam.
Masking may work but it will reduce the efficiency of the system.


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## gcbryan (May 5, 2010)

I've requested that it be moved. I remember a post with Saabluster (or whatever his username is...maker of the DEFT) and he mentioned that aspherics could be much better than they generally are and that using plastic such a lens could be designed so that beam quality was any way you wanted it.

The point was that optics were better than reflectors in general but that the optics that would meet anyone's expectations are generally not found in flashlights.

He pointed out that a lens could have built-in diffusers and well as clear areas. An optic could shape the beam in any way that one wanted. That gave me the idea (since I couldn't custom make my own lens) to use masking to achieve a similar result.


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## saabluster (May 6, 2010)

gcbryan said:


> I've requested that it be moved. I remember a post with Saabuster (or whatever his username is...maker of the DEFT) and he mentioned that aspherics could be much better than they generally are and that using plastic such a lens could be designed so that beam quality was any way you wanted it.
> 
> The point was that optics were better than reflectors in general but that the optics that would meet anyone's expectations are generally not found in flashlights.
> 
> He pointed out that a lens could have built-in diffusers and well as clear areas. An optic could shape the beam in any way that one wanted. That gave me the idea (since I couldn't custom make my own lens) to use masking to achieve a similar result.


You rang? I have experimented with many optical solutions. As you know I made lenses with the diffuser built into the lens. I can also make them half and half but it does reduce the throw and people around here don't like the idea of less throw.


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## gcbryan (May 6, 2010)

If more flashlights were made using aspherics I think it would be interesting if a typical flashlight came with 3 lenses. 

One would have a diffusion effect over the entire lens so this would be for indoor use or outside when only illuminating the immediate area is a concern. This lighting would be very pleasing to the eye.

Another would have the hotspot clear and the rest of the lens would be diffused. This would have the most throw.

The third would have a uniformly graduated diffusion meaning the very center of the lens would be relatively clear and as you move out toward the perimeter it would get more and more diffused. This would be very pleasing to the eye as well but there would be some throw. This would be the "general purpose" lens.

Saabluster, have you ever experimented with using a "variable lens", just to coin a term here, with a reflectored light? I'm not talking about combining a traditional aspheric with a reflector but rather with the scenario in one of my other posts above. Using a lens to soften the hard outer edge of the spill and to soften the perimeter of the hotspot (if either of these things are even possible this way).


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## saabluster (May 6, 2010)

gcbryan said:


> Saabluster, have you ever experimented with using a "variable lens", just to coin a term here, with a reflectored light? I'm not talking about combining a traditional aspheric with a reflector but rather with the scenario in one of my other posts above. Using a lens to soften the hard outer edge of the spill and to soften the perimeter of the hotspot (if either of these things are even possible this way).


As you may know most of my time is spent pondering lenses but I did develop a method of selective diffusing for reflectors about a year and a half ago. I realize that is awfully vague but I will just leave it at that as I would like to keep my designs quiet for the time being. Not that I have any product with that design in mind but I would like the opportunity to recoup the massive R+D I have done should a company want my design services.

On a topic more related to the thread title I worked out a way to successfully combine a reflector and an aspheric lens. Whenever anyone asks about combining the two the answer is always "don't do it!" and for good reason. The artifacts that setup creates are horrendous. The idea behind it is a good one though. So much light is lost to the sides in a normal aspheric setup that people see the opportunity to get more lumens out of the light by using a reflector to gather them up. Most people just combine the reflector that came with the stock light and add an aspheric over that=:sick2: 

There are three things I found to make it work. First off is the LED used. It needs to have very little between the edge of the die and where the reflector can start. The smaller the gap the better off you will be. In this respect the XP-G is about as good as they come. Next you need a very small reflector that has a bottom opening no larger than it has to be to allow the LED to fit inside and reach the focal point. It also needs to be matched with the aspheric on the output side so that it gathers as much "wasted" light as possible but does not steal light from the main lens. Lastly you need to add just a hint of diffusion on the aspheric. This will vary based on how well you did combining the other elements. 

The resultant beam is very nice with a very bright hotspot that blends beautifully out to what might be better called the corona than the spill as all of the light in this setup is receiving collimation of one sort or another. It really does make a nice beam.


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## gcbryan (May 6, 2010)

Interesting Saabluster!

I have heard, but haven't seen, that the Wolf Eyes Krait and Led Lenser's both use reflectors in addition to their aspherics. I don't even know if this is true and if true I know nothing about what kind of reflectors are used.

Someone, in other thread, mentioned that most reflectors are parabolic but that another reflector design was more appropriate for this particular application (I can't remember how they described this reflector...rectangular?). Anyway, their expertise was in optics theory but not necessarily specifically with flashlights. Sorry, but I just can't remember the details.

Even though I'm sure I was wasting lumens big time with the crude changes I made it was interesting to see the change in the beam.

Just a partial masking with translucent tape, and painting the silver ring on the XR-E along with painting the reflector got rid of all of the artifacts. Painting the reflector, since I couldn't remove it, was a given from the start. The other stuff was playing it by ear but was interesting.

I didn't have an accurate way to measure how much throw I was losing. I had to be of course but it wasn't obvious to me. I had one lens that I didn't change and I kept putting it back in as a control every time I changed the other set-up.

The light on target did change. With the ugly beam, although it seemed to throw the same distance as the "pretty" beam, the light on target was greater in diameter.There was the hotspot image of the emitter and then a larger bright area around that.

With the cleaned up beam there was only the emitter image on target. To me it was a good trade-off.

Of course, if I had better components that would have been even better but at a certain point you have to make the best of what you've got...including components, experience, and skills or lack thereof. 

Feel free not to answer this question as I know you don't want to talk about the reflector design you have but if you can answer that's fine too...your process to improve reflectored light output...is it a process that you've come up with to directly change the reflector or is it a lens that you've developed to put over the reflector to give the desired results?


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## Th232 (May 6, 2010)

Very interesting stuff Saab! I've got a torch I'm building, gap for the optics is about 17 mm dia by 20 mm long. Small, so throw won't be the best, but do you think there's much hope for me getting it to work? Got a couple of 17 mm aspherics, only query now is to find the reflector.

Out of curiosity, have you tried doing the opposite, i.e. where the reflector is the main component? Kinda like what Polymer Optics has done here by putting a small lens in the middle of a reflector:







As gcbryan said, if you'd prefer not to share your info, I fully understand why.


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## gcbryan (May 6, 2010)

TH232, that's kind of the same concept of a TIR isn't it. Small lens, large reflector. In any event my DX version of a TIR is an optic of course rather than a traditional reflector but it has a small collimating lens over the emitter which is what the optic you've pictured is doing I'm guessing.

Both are reducing spill and redirecting the light that would miss the reflector.


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## Th232 (May 6, 2010)

Pretty much the same in that there's both a reflecting and a refracting component, but I think the approach is slightly different.

It seems that while the effect is pretty much the same, what Saab is doing (and correct me if I'm wrong Saab!) is using a small reflector to redirect what is missed by the aspheric (main component is the aspheric), while this one is going about it the other way, it's mostly about the reflector, with the lens being a secondary component (e.g. it's a fresnel lens).

In short, I think Saab wants maximum throw (hmm... what's this DEFT thingamabob I've seen ), and whatever he can gain in efficiency is an added bonus, while the other method is to balance throw and efficiency, or maybe just maximise efficiency.


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## bshanahan14rulz (May 6, 2010)

Aspherics throw an image. If you had supereyes, you would see the same pattern projected by a reflector-aspheric setup as you would if you were looking straight into the light (I.e. you'd see the LED in the center and the reflected light on the reflector.)

What Saab's setup does is project this image, but the texture to the lens smooths the gap between the LED image and the reflector image, creating a hotspot(image of LED) and image of the reflector


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## Walterk (May 22, 2010)

If throw is not the ultimate, overfocussing (the led to close to the beam ) is pretty sharp and even, I like that a lot, better then reflectors. Escpecialy with adjustable focus. There is a lot experimented in the 'design road headlight' threads.

If you would use a precollimator, according the principle of an inversed refracting telescope (wiki refracting telescope), you can catch-off all disturbing spill at the crosspoint of the light rays. This principle is also used in beam-expanders for lasers, it is named a spatial filter. Actually it is just a pinhole on the crosspoint where the beam is at its smallest diameter. You only want to use the rays that go through this hotspot, as these are the only ones that are aligned well enough to enter (and leave ) the second lens at the right angle.
The rays that are not passing the pinhole, are the rays that would otherwise be expelled at random angles instead of the desired beamangle, giving spill light.
The inverse of the pinhole, a ring on the outside of the total beam, is also working as a spatial filter (See Wiki 'spatial filter' for theory ). 
















There is a issue that not with all principles the rays cross each other.
On the other hand, a series of black painted shield-rings (as in the Huygens sketch) should catch-off scattered light also quite well. That is how they do it in the large zoom-lens housings. 

The advantage for using two lenses, is that it is easy to find low-f-number-large diameter lenses for the front lens, and the first can be very small so probably will be not costly. 










The Deft for example uses the Huygens telescope, by having two plano lenses in row. The Huygens telescope eye-piece (named oculair, functioning as condensor ) is a simple, two element design that had 'very short eye-relief and a very restricted field of view'. (Think reversed here. ) The Ramsden principle is also 2 plano lenses, but with kind-off-spatial filter in front.(It looks to me this set-up can be recognized from all sorts of condensor-assemblys in projectors.) 

CPFmember Long John proving the pre-collimator concept:
*HID-Killer: Adaptor for 1xCree light*

Wiki about telescope eyepiecs, (see Huygens using two aspherics):
http://en.wikipedia.org/wiki/Eyepiece

About eye piece principles:
http://www.funsci.com/fun3_en/ucomp1/ucomp1.htm

Also see this about beam expanders:
http://stwww.weizmann.ac.il/lasers/laserweb/Ch-8/F8s1t2p11.htm
http://electron9.phys.utk.edu/optics421/Laboratories/Lab2.htm


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## 007adan (May 24, 2010)

As far as pre-colllimators go. I'm going to give this fella a whirl.

http://www.dealextreme.com/details.dx/sku.13570

It will sit very close to my Xre-R2 led. with a 66mm Aspheric as my outer lens. Any suggestions????


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## Walterk (May 25, 2010)

My guess is the first and small lens to have a considerable smaller f-number then the larger front lens.
Please post your findings once you've tried !


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## TorchBoy (May 25, 2010)

Walterk, what's up with the two picture links in post 12?


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## Walterk (May 26, 2010)

deleted


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## TorchBoy (May 27, 2010)

Was that supposed to be in response to my question about the picture links?


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## Walterk (May 27, 2010)

Yes it was, the images illustrating what the links are about.


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## TorchBoy (May 27, 2010)

They are *missing* images, not images. Did you link to something on your local network?


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## Walterk (May 27, 2010)

Sorry, I misunderstood you there. They are links to websites with 'the full story' and not display a specific picture.


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## TorchBoy (May 27, 2010)

They are both non-working links to GIFs, you nana. 



:laughing:


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## Th232 (May 27, 2010)

Specifically, the two gifs you posted with these links:

http://1.1.1.2/bmi/stwww.weizmann.ac.il/lasers/laserweb/Ch-8/8-8.gif

http://1.1.1.2/bmi/electron9.phys.utk.edu/optics421/Laboratories/images/expander.gif

Are not working.


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## Walterk (May 27, 2010)

I understand you guys have a problem with some links I posted.Although they work fine for me from the country where I live, ( independent of ISP and PC at work and at home ),I added and changed some links to alternative pictures. I keep the other links for the time being.

The concept is simple and when you see it, you understand it.
The use of two lenses requires some experimenting but obviously increases throw.


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## TorchBoy (May 27, 2010)

Walterk said:


> I understand you guys have a problem... :nana: As you understand for me all pics and links work fine.


Because they were on YOUR network you nana.  :whoopin:

Thanks for fixing them.  Although... you've left the bad links there. 

:lolsign:


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