Aspherical Lens for small flashlight

Where can I find an aspheric shaped lens for my Ultrafire R1 flashlight? Where do people buy aspheric lenses anyways? I have run a search and I can't seem to find anywhere that sells them.

Dan K

surplusshed.com has some. I used a small aspheric in my Eastward YJ U2 cree light and was disappointed with the results. I tried it with and without the reflector. I could get the beam to project a real clear die image of the LED but it was not as bright as I would have hoped. My hotspot was brighter with the reflector actually so I switched back. I'd be interested to see if anyone else has had much luck with the smaller aspherics.
Fletch

thanks a bunch fletch! I'll check it out and see what it has to offer.

1. The smaller the lens, the bigger the spot.

2. The radiation pattern of the Rebel Led in the R1 is inappropriate for an
aspherical setup, you will be disappointed …


tl

I want to say that the diameter is roughly between 20 and 22 millimeters, and the width is probably 1 to 2 millimeters. I can't say exactly, so if anybody knows the exact dimensions of this lens and where I can find an aspheric lens that will fit this light, that would be killer. It's powerful, but I could use more throw out of it!

Dan K

taschenlampe said:

1. The smaller the lens, the bigger the spot.

2. The radiation pattern of the Rebel Led in the R1 is inappropriate for an
aspherical setup, you will be disappointed …


tl

Click to expand...

danke freunde

I live near Surplus Shed and a few weeks ago I picked up 7-8 different lenses to try in my Mini-Mag TLE-5EX. I tried aspheric and Plano-Convex, and was pretty disappointed by all of them.

I found the reflector/twist head does a better job of focusing than any of the lenses I tried. Since the flashlight head doesn't have much threading, you're limited to lenses with very thin edges (which eliminates a lot of potential lenses that might give better results but won't fit).

I put the borofloat I got from FlashlightLens.com back in (even though it doesn't focus at all).

closest one that focuses well of that size i have tried is

the "18mm" one L3694
http://www.surplusshed.com/pages/item/l3694.html
its actually 19.1mm in diameter and 6.65mm tall.
the focal length that the top of the led dome needs to be from the bottom of the lens is about 10mm.
there is no lip around this one
fits a coast David 19 almost perfectally, a bit of carefull grinding and it socks into the head pressure fit.


next one up i have tried is about 24-25 acrylic halfdome from tap plastics or your craft store. what would that be a 3/4" halfdome?

acrylic balls work too, cheap for experimenting.

when you look for them the very high dome ones are working more often than the just a magnifying lens ones.
specialty flashlight parts sellers are going to get something in? a 22- 23mm, read it somewhere this week.

and my measurements are NOT as close as my decimal places, i only have a junk caliper thing.

there is one that is teeney and looks perfect size for a fenix, but i cant get the (*#$^@) fenix head off without damaging something.

taschenlampe said:

1. The smaller the lens, the bigger the spot.

2. The radiation pattern of the Rebel Led in the R1 is inappropriate for an
aspherical setup, you will be disappointed …


tl

Click to expand...

great just got some for this light.damn.:green:

If you want an optic based Cree torch take a look at:
Elektro Lumens Lucidus-XR3 (3AAA)
Elektro Lumens DeCree (18650)
I was quite impressed with my XR1 (1AA). When I tried a 14500 WOW. Brightest REASONABLE SIZED hotspot. The spill light is dim, just barely sufficient to avoid stepping into potholes/gopher holes.
EDIT
Electrolumens decided to use a SSC-P4 with a reflector instead of the Cree XRE with optic on future orders so my suggestion no longer applies,

RE: Cheap DX light of some sort
Maybe you should change that to Most reliable DX light of some sort.
A lot of the DX/Kai/Dae have problems - flaky clicky switches, bad tolerances/finish, flaky electronics , no workee with 1.2V NiMH batteries etc. It takes a lot of work to go through the review and comments threads to seperate the wheat from the chaff. Once you can find a working one the brightness can equal much more expensive lights.

taschenlampe said:

1. The smaller the lens, the bigger the spot.

2. The radiation pattern of the Rebel Led in the R1 is inappropriate for an
aspherical setup, you will be disappointed …

tl

Click to expand...

1. Until you get to the diffraction limit (and these Aspherical lenses don't even come close by many orders of magnitude), the spot size is determined by the FOCAL LENGTH, not the lens diameter.

2. Do you know something that I don't about the R1? The reason I ask is because the stock rebel uses a Lambertian pattern which will work FINE with low F-Ratio aspherical lenses. Does the R1 use a custom flat top wide angle Rebel or some other wierd variant? An F1.0 Aspherical lens (focal length same as diameter) should capture more than half the luminous flux from a Rebel and lower F-Ratio lenses can capture 2/3 or even 3/4 (this is much more than the reflector captures in most lights). You might get a little higher capture by using the Aspheric with a CREE XRE P4 series but I don' t like the funny "square with another little rectangle bolted on" pattern that is thrown by the CREE (bad enough that you have to deal with a square instead of round hotspot when the light is tightly focused, without haveing to deal with that!) The Rebel 100 will output so damn much light that the losses just won't matter and it has a nice square pattern.

Sorry to be nitpicky about the optical info, but anyone doesn't take the time to learn a few basic optical principles, and who just orders some random lenses based on "What will fit", is bound to be disappointed.

For example, you can get a really SMALL 'spot size' with a longer focal length lens, but if the diameter of the lens is the same, then increasing the focal length will reduce the F-Ratio and DIM the image.

Here is a quick reference.

- Spot Size is proportional to the FOCAL LENGTH of the lens verses the DISTANCE and has no direct relationship to the diameter of the lens.

- Brightness and light capture efficiency are inversely proportional to the F-Ratio, which is the Focal Length divided by the Diameter (i.e. Low F-Ratios are better). These lower F-Ratio lenses are easy to recognize because they are more strongly curved, and thicker in the center.

Let's look at that 'Spot Size' / vs Lens Size issue in light of the above rules (and some actual experimental experience with other lights).

With 50 mm diameter 35 mm focal length lens (F0.7) the actual empirical data, from folks that have actually built them, indicates that an Aspheric Maglight can easily provide useful illumination over 100-200 meters or more.

A relatively tiny 17mm diameter 12mm focal length (F0.7) will capture about the same percentage of light from the LED emitter (remember it's F ratio not diameter) and the spot size will be almost precisely 3 times bigger.

That means that instead of lighting things up 1 or 2 hundred Meters away, your tiny pocket light will only manage to reach out 30 to 60 Meters or so.

This seems like pretty reasonable performance to me, but, there is another reason entirely to NOT convert small fixed focus lights to an aspheric.

A light that is ALL THROW and no SPILL is just not very useful (trust me on this, I have one).

Of course, you could set the light up instead for a larger spot size with some fill (which can be done by painting the inside of the head white and slightly defocusing the aspheric optics), but this will negate much of the advantage of the aspheric lens (and you will still have a light with very little spill).

This is another very important lesson in building a successful aspheric - The flashlight needs to be designed around the Aspheric lens, not the other way around.

So, I would recommend that if you want to build a really effective small aspheric light, start with a Mini-Mag which has adjustable focus.

This will give you a light that can be defocused on demand to give a quite nice flood, and which still can be focused down to provide very good throw when you need it.

All that is needed is a good Rebel based mini-mag drop in (the cree is to large, and the SSC has a wider pattern that would not work as well).

So it would seem that we can draw two conclusions . . .

1. Aspheric lens CAN provide very good performance in small lights, if you pick the light for the lens, not the other way around.

2. The Rebel LED is a great choice for these lights.

thanks guys i am going to try the lens on the R1 with not much hope now.but what about the D-MINI any thoughts.:thinking:

taschenlampe said:

Let me try it the other way.
If you have two aspheric lenses with the same F-Ratio - a big one and a small one - then the small one will project the bigger and less intense Spot!
Agreed?

Click to expand...

Oh, I see, all the lenses at surplus shed (and everywhere else on earth) are all the same F-Ratio anyway, so I guess we can safely make this simplification.

Wait! That's not true.

Then why give people the impression that all that matters is the diameter?

taschenlampe said:

With the R1 one only can use a small lens …

Click to expand...

Yep, and you can also only use a small reflector.

I made the point that a aspheric lens 1/3 the size will have 1/3 the throw, which could still amount to 30 to 60 meters (which is much better than the stock reflector in these small lights).

taschenlampe said:

If I remember right the typical radiation pattern of the Rebel is 160°. An aspheric lens with F-Ratio 1 will capture a cone of light of about 50° - in my opinion this can't work!

Click to expand...

Works just fine.

As far as your memory goes, if you are worried about the difference between 99% and 100% we can talk about 160 degrees, but the Lambertian pattern looks a bit like the classic 'bell shaped curve', and is pretty highly center weighted, and we need to take this into account.

Also, your simplified geometry is just a bit off.

Obviously you are just accounting for the inverse tangent of half the lens diameter/focal length times two (which would be about 52 degrees).

The actual geometry is shown below: (figure is borrowed from another post, thanks wintermute!).






Here you can see that fb is actually significantly less than f, because f is measured from the center of the optical axis, not the back of the lens.

With light refracted at both surfaces of the lens, even light hitting the rear surface of the lens fairly close to the edge will be captured.

Because fb is less than f, the capture angle will be wider.

The Rebel's lens also affects the focus. This requires that the Rebel be brought FORWARD from the focal plane position shown as F above (to bring the LED die back into sharp focus).

For a low F-Ratio lens, these factors will reduce the distance fb by a full centimeter or more over f.

Also all of the above was just a worst case F1.0 example anyway, because low cost F0.7 lenses are easily obtained.

taschenlampe said:

It will not output more than an SSC P4 U-bin but it has a wider radiation pattern, so I can't believe that it will work - The SSC did not work well with aspheric lenses - trust me, I have tried it.

Click to expand...

I think you have that backwards.

From my PDF docs for the SSC and Rebel, it looks like the SSC is the one that is about 16 to 18 degrees WIDER than the Rebel at the half power points (not the other way around).

SSC is best suited to a reflector, but could be used with secondary optics to reduce the beam angle.

I am not surprised you had trouble with it though, given some of your assumptions.

taschenlampe said:

Yes - with a CREE - but NOT with a Lambertian Emitter.
With a Lambertian Emitter a well-built 50mm reflector will give a way better performance!

Click to expand...

When you are thinking about that wonderful reflector, remember the Lambertian pattern is center weighted, and NONE of the center pattern spill light that exits though that nice big hole in the front of the light ends up in the hot-spot contributing to the 'throw'. This spill light which doesn't contribute to the spot beam, is usually 50% or more of the emitters total output.

You would need a nice deep 'custom' reflector to capture as high a percentage of light as a F0.7 aspheric lens will capture from a Rebel.

Do you know where I can get such a reflector for the 8 dollar price of an aspheric lens from surplus shed?

In any case, if it worries you that much, and you want a tighter pattern from the Rebel it's easy and cheap to get.

You can get secondary optics from these folks for only a couple Euros, that will reduce the beam angle to only 25 degrees (presumably at the half power points, though I couldn't find a detailed plot).

http://www.led-tech.de/en/Luxeon-Hi...r-Luxeon-Rebel-lense-25%B0-LT-1090_49_85.html

taschenlampe said:

My opinion: I would recommend using a Cree, each Lambertian LED will be inefficient …

Click to expand...

The CREE is about as much narrower compared to the Rebel as the Rebel is compared to the SSC. (Rebel falls in the middle between these two).

I said that the CREE was a good choice if you can live with the funny shaped spot image, so if you can find a nice mini-mag drop-in using the CREE go for it!!!

Luminescent said:

... I think you have that backwards.

From my PDF docs for the SSC and Rebel, it looks like the SSC is the one that is about 16 to 18 degrees WIDER than the Rebel at the half power points (not the other way around). ...

Click to expand...

I don't think so ...

Relative Intensity in % @ +/- 30 deg. :




tl

nice, i like color coding like that, picture i can understand

as far as the emitter Pattern, the cree indeed has tracks, but the NEW 100 rebel has Squares too, the old rebel (80) doesnt have the squares

of course defocusing a tiny bit and you dont see the emitter pattern, but as far as pattern goes, the new high efficiency stuff is using that pattern to GET to high efficiency, something to do with getting the light out PAST the phosphors, instead of bashing light that was headed out into them.

i have always thought that the "dome" that causes most of the light to hit the lens would be the best item for hitting a lens. defocused on WIDE, and the LED is much closer to the lens, and then most of the light gets out anyways.

using optics to get the light to the lens, has never worked, on the stuff that i tried, so your normal led optics that conform the light to a 5-25* beam, dont help nothing.

taschenlampe said:

I don't think so ...

Relative Intensity in % @ +/- 30 deg. :

Click to expand...

Huh?

The graphs you just posted for the SSC disagree with the one in the PDF manual I have been using, so I just crosschecked them against those in the most current manual from the Seoul site for the P4 (PN 42180). I am not sure where you got that data, but in any case, even the data you showed indicates the Seoul is much wider than the Rebel, so your assertion that the Rebel was wider is obviously flat wrong.


Here is a brief visual quote [for editorial purposes] directly from the CURRENT SSC P4 data in the Seoul PDF documentation . . .




I have marked the above figure up, as you did, but I have used the STANDARD half power angle.

As you can see the P4 hits half power at about 67 degrees off axis.


The Rebel Lambertian radiation pattern is essentially a raised cosine function plot, here's a good reference that explains how it is derived:

http://www.phas.ubc.ca/~mackay/phys404/documents/BiomedicalOptics/ece532/class1/lambertian.html


Your posted info for the Rebel agrees with mine, so I have just re-ploted the lines to agree with the same standard half-power angle shown above for the SSC P4.




Here you can see that the Rebel hits 0.5 at about 58 degrees, which is quite close to the 60 degrees predicted by a perfect Lambertian distribution.

67 degreesSSC - 58 degreesREBEL = 9 degrees(HalfAngle)

And . . .

9 degrees(HalfAngle) x 2 = 18 degrees(FullAngle)

So you can see, when I said that the SSC was about 16-18 degrees wider than the Rebel (not the other way around as you had stated), I was NOT just pulling numbers out of the air.

Any questions ?


Finally as to backing up my claim that a 0.7 lens can capture a useful amount of light (60 - 70 percent) from a Rebel . . .

taschenlampe said:

Another try ...

A lens with a back focal length of 0,7 collects a cone light of about 70 deg., 35 deg. on each side.

Click to expand...

I'm not sure why I bother posting this information, because you obviously weren't paying attention when I explained that you can't just use the focal lenght and diameter directly to calculate the geometry.

Due to the factors I mentioned in my last post, the 'Lens-to-Rebel' distance for a 50 mm diameter 35 mm focal length F0.7 lens will actually be closer to 25 mm than 35 mm.

This works out nicely because you can then easily do the trig in your head because each side of the focal geometry becomes a perfect 1:1 25mm height / 25mm base right triangle.

Obviously then the half angle light cone coverage of the lens then becomes 45 degrees (90 degrees full angle).

Here as a simplified 'Area Under the Curve' plot at this 45 degree half-angle, for a Rebel Emitter so you can see how it works out . . .




In the figure above, I have subdivided the total area under the curve into 7 approximately equal sub-sections.

2 of these areas fall outside the light cone of the lens and 5 fall within it.

5 / 7 = 0.714285 or approximately 71 percent.


Of course you could nitpick that the #5 top area looks a little smaller (actually, I think it's larger), but clearly the number is between 60 and 70 percent any way you slice it.

This is more energy than ends up in the hot-spot with a reflector based system.

Yes, the a CREE X-Lamp X-RE 7090 series emitter will manage to put about 15%-20% percent more light into the lens, but this small improvement would be almost completely unnoticeable by eye, and for me is just not worth it, due to the asthetic issue I mentioned with the oddly shaped image when the CREE LED die is in focus.

So the bottom line is . . .

Geometrically, a F0.7 aspheric lens will capture MORE useful 'hot-spot' light from a Rebel emitter than a typical reflector based light (which looses half or more of the hot-spot light out the open front of the reflector as 'spill').

The aspheric lens is MUCH more effective in focusing this light.

This relationship still works for smaller lenses as long as the F-Ratio is the same (0.7 or less), so aspheric lenses in these smaller lights can STILL outperform reflectors on raw throwing power.

VidPro said:

nice, i like color coding like that, picture i can understand

as far as the emitter Pattern, the cree indeed has tracks, but the NEW 100 rebel has Squares too, the old rebel (80) doesnt have the squares

of course defocusing a tiny bit and you dont see the emitter pattern, but as far as pattern goes, the new high efficiency stuff is using that pattern to GET to high efficiency, something to do with getting the light out PAST the phosphors, instead of bashing light that was headed out into them.

i have always thought that the "dome" that causes most of the light to hit the lens would be the best item for hitting a lens. defocused on WIDE, and the LED is much closer to the lens, and then most of the light gets out anyways.

using optics to get the light to the lens, has never worked, on the stuff that i tried, so your normal led optics that conform the light to a 5-25* beam, dont help nothing.

Click to expand...

Generally I agree that these add-on optics are not usually a good idea.

The design becomes quite critical, and you can only get an improvement if the main lens is loosing a lot of light because the secondary optics also have losses.

To get the secondary optics to work they have to be carfully integrated with the main lens, and the composite system will have a focal lengh that is SHORTER and therefore throw a LARGER spot.

So, secondary optics are not about throwing a smaller brighter spot, they are about thowing a larger spot that is just as bright.

Though some go nuts, trying to get the smallest spot possible, it's really about how brightly you can illuminate far away objects, and it would be foolish not to go for a larger spot if it is just as bright, and with very careful design, sometimes this can be achieved.

Also thanks for making the point about the New Rebel 100's.

I have some of them, and they do indeed have a few checkerboard squares in the pattern. These are very easy to knock out of focus, and I don't find them to be as annoying as the asymetric CREE pattern, but some may feel otherwise.

I suppose it wouldn't be too hard to put in a focus stop in your custom Aspheric light to limit the focus range so that the nasties from either type of LED don't ever show up, though that would limit you to a slightly larger spot and give up a little of the advantage of the Aspheric.

From my experence, even with this limitation the Aspheric would still outperform a reflector based light by 2 to 1 or more on throw.

Also as you noted, the best way to get FLOOD is to defocus towards the lens, which helps get almost all of the Rebel's light through the optics and totally eliminates any funny patterns.

i have written down that the 52mm (best) surplus shed lens has a best focus at about 20mm (from the TOP of the cree dome), but physically holding it in place and getting a quick measurement was all i needed to see.
so i would think it is more around 25mm than 35mm.
depends if your measuring from the emitter or the dome top.