# Aspheric and xml at 2800ma

#### Goldigger

##### Enlightened
Quick beam shot here guys, was up the woods doing some beam shots with the new XML led

Used one of athortons aspheric lenses

#### busylifemeto

##### Newly Enlightened
Fantastic result and yeah the XML is something, can I ask what size Aspheric you used ?

Nice work !

#### Codiak

##### Enlightened
Fantastic result and yeah the XML is something, can I ask what size Aspheric you used ?

search for ahorton sales

#### Codiak

##### Enlightened
Very nice....

How far off the top of LED was the aspheric?

#### Goldigger

##### Enlightened
Very nice....

How far off the top of LED was the aspheric?

It's one of the ahortons 30mm aspherics..which are now 27mm.

#### Klem

##### Enlightened
I'm starting to appreciate how focussed aspherics are compared to reflectors and TIR optics for LEDs. Nice tight beam!

Here's a general question on your topic...

I'm thinking the focal point of an ashperic changes according to the LED's beam angle. For example the focal point of an XR-E at 90 degrees should be further away than an XM-L at 120 degrees, using your 27mm aspheric, yes? What about the curvature of the aspheric? Is that not a variable in the focal length as well? And is there a set curvature that all aspherics conform to?

What I am getting at is an arbitrary aspheric dome curvature could cause inneficiencies in the collecting of light. I calculate that if your aspheric is 15mm from the LED and with 24mm of usable curvature (27mm in diameter with say a 1.5mm lip would be a 24mm aspheric) then it collects only 78degrees of your LED's beam. If the XM-L emits at 120degrees then the edges of that beam are not captured and focussed by the aspheric.

And if that's the case would not an aspheric sitting on the end of a reflector (at the correct focal point) be more efficient than an aspheric sitting on the end of something like non-reflective plastic or metal tubing?

#### Codiak

##### Enlightened
Klem,
Short answer is it seems logical and exactly what I've been experimenting with. Technically isn't this just a tir implementation? Discoloration of the beam is idling me right now!

#### Klem

##### Enlightened
I wouldn't have thought so. TIR is a cone of solid material with a flat top, whereas an aspheric on the end of a hollow reflector is something different again...surely?

If the aspheric is at the focal point in front of the LED, yet there is light being emitted wider than the diameter of the aspheric then a reflector would deflect that forward into the aspheric. All light should be captured.

#### srfreddy

##### Enlightened
Oh god.... An aspheric lens collimates a point source. Obviously, an LED is not a point source, but it is very small, and the lens "projects" the image of the LED out the flashlight. A reflector focusing light into an aspheric lens is certainly NOT a point source: the result is a bunch of chormatic abberations and concentric rings.

#### Klem

##### Enlightened
Unsure what God has to do with it but side spill is usable light heading forward of the torch, as opposed to being lost through a lack of reflection inside the torch.

#### Packhorse

##### Flashlight Enthusiast
Unsure what God has to do with it but side spill is usable light heading forward of the torch, as opposed to being lost through a lack of reflection inside the torch.

I think what srfreddy was trying to say is you will end up with one ugly beam.

#### Klem

##### Enlightened
Point taken, but if the opportunity-cost of having those mutiple rings around a central focussed square is you don't have them, then underwater I would probably want them.

For me, form (in this case the aesthetics of the light footprint) is of lesser concern than function. When you consider there is no spill to a focussed aspheric and this is where you could have your cake and eat it. You don't compromise the max possible lumens of the throw, while adding the light that would otherwise be lost.

#### Codiak

##### Enlightened
Point taken, but if the opportunity-cost of having those mutiple rings around a central focussed square is you don't have them, then underwater I would probably want them.

For me, form (in this case the aesthetics of the light footprint) is of lesser concern than function. When you consider there is no spill to a focussed aspheric and this is where you could have your cake and eat it. You don't compromise the max possible lumens of the throw, while adding the light that would otherwise be lost.

I can't disagree with want the desire to maximize output vs waste. And put a reflector in seems to improve output, but gives a reverse donut effect with various color tones.

However diving conditions and use for the light certainly determines the effectiveness of the beam.

For camera work the multiple tints sux
For low vis the spill sucks
And square beams just aren't acceptable to some people

I'd really whisk led would get off their arses and release the 4 degree optic
Or some would make a really deeeeeeepppppp reflector for the XML

Back to the OP. What difference is there is refocusing by moving away from the asperhpic vs closer? I've de focused it at 6.5mm and it looks good

#### Packhorse

##### Flashlight Enthusiast
I'd really whisk led would get off their arses and release the 4 degree optic

Most are 120 degree. XR-E is 90 degree. You expect them to release a 4 degree? 5mm LED's seem to have the tightest focus of any LED. Chuck one of those behind an aspheric and see what happens.

Or some would make a really deeeeeeepppppp reflector for the XML

I really like the W300 deep reflector. works great with a MC-E and SST50 ( or is it a 90) I have.

#### Codiak

##### Enlightened
Most are 120 degree. XR-E is 90 degree. You expect them to release a 4 degree? 5mm LED's seem to have the tightest focus of any LED. Chuck one of those behind an aspheric and see what happens.

The XM-L is the right balance of power vs output, it just needs better focus. AHorhton's asperic is doing nicely.

That doesn't change the fact that Ledil issued a press release and samples for a XM-L 4 degree optic months ago. Since then they have gone quiet and pulled the product references from their website.

So yeah you could say I believe it's possible and is only matter of when... btw that optic was 37mm I believe.

By deep... What I envision the beam to look like would require a reflector that isn't practical for a handheld dive light. I sent a PM to Phoenix Reflectors asking about design a month ago... nada.

#### ahorton

##### Enlightened
Just my thoughts about focal length and beam angle: I don't quite think they're related in the way that klem suggested.

Consider a perfect point source against a non-reflective wall (light emitted at 180 degrees in any 2D plane containing the point source emitter). Bring in the lens and you'll find a focal length.

Now put the point source behind an aperture that blocks all light except the central 90 degrees, or 45, or 17, or 3.445 etc. In each case the focal length will be the same (though the total flux will be different).

The only thing that matters to focal length, is where the point source is, not the range of angles that light can leave the emitter. Of course we don't have a point source and thanks to the silicone / glass lens that comes with your favourite LED it's not trivial to calculate where the 'virtual' emitter actually is. So we put down the calculator and try it out. Even knowing the exact curvature of the aspheric surface, I don't bother trying to calculate how far it should be from an LED.

As for the reflector, you get some kind of image of the reflective surface and you don't want to know how ugly that is! For most of the reflectors you get in modern flashlights, you'll find them far too deep anyway (for the aspheric to be at its focal length). So you need to cut them down and then they're too narrow to allow much light to pass through the lens.

For the XR-E it was never worth it, but for the XM-L you may benefit from a very, very wide reflector that sends light around the edge of the lens. However, for the space it takes up you could just put in 2 more XM-Ls with their own lenses.

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#### Klem

##### Enlightened
So what you're saying is that the focal point is predicated on the curvature of the lens, not beam width.

If that is the case then I suppose if some clever torch manufacturer were to get in contact with a lens maker and stipulate the width of the beam (say 120 degrees for an XM-L) and suggest the shortest possible focal point is the most beneficial (=smallest diameter, shortest torch head), then they would stand to have a torch with the most efficient throw

#### ahorton

##### Enlightened
Yes the focal point of the lens is totally dependent on the curvature of the lens and the speed of light in both the lens and the mediums (eg air or water) on either side.

As for the second statement, there's a bit more to it I'm sorry. The shortest focal length possible is infinitely small (basically 0mm). To get this you have to make an infinitely small lens which effectively catches no light at all. From a perfect point source it wouldn't matter, but our LEDs are much bigger than a point. ... long story short ... For efficient throw (read collimation) we want to make the emitter look like an infinitely small point to the lens. This means making an infinitely large lens which is not cost effective for flashlight manufacturers (but maybe possible for a one-off custom job).

Also note that along with short focal lengths, we want a wide diameter to collect light. So you want the highest diam / focal length ratio. Though beyond 2, you get no more returns because light is reflected.

...Sorry, I get carried away.

#### Codiak

##### Enlightened
...Sorry, I get carried away.

The passion shows in your posts and products, nothing to appologize for.....