Aspherics?

[gcbryan]

Most lights today use reflectors but a fair number do use aspherics. Are they as inefficient as I think they are and is that why we don't see more aspherics or do you think we will see even more aspherics in the future?

I don't like the rectangular shape but you can slightly defocus them to correct that. One downside seems to me to be that some light is wasted with aspherics in general and even more if you defocus them.

The main advantage seems to be for throw but most lights throw well enough for general use and for extreme use there are probably better ways to get throw than by using leds in the first place. Extreme throw with a tiny spot of light doesn't seem all that useful to me.

So, do you think apherics are more of a phase or will they be around in numbers for a long time?

The complete lack of spill hinders their usefulness as well in many cases. I personally see TIR as being a more useful optic than aspherics in many cases (you reduce spill which is generally good for me but you still retain some).

I'm just trying to get some other viewpoints regarding aspherics. Feel free to comment on the usefulness (or not) of aspherics and throw with leds. Many posts seem to be looking for greater than average throw but I'm not sure why it's all that useful considering the small spot that you end up with even if you needed throw.

 

[rayman]

I find aspherical lenses not very practical. I like them a lot because it's just fun to get the most throw out of a flashlight but it's just not practical as it mostly is pure throw. A thrower with a normal reflector has some spill around the hotspot which an light with an aspherical lens doesn't. Another reason would be that you have to protect the lens from damages which will make the light much bulkier.
On the other hand a focusable light with the right aspherical lens can be quite practical as you can focus the beam from flood to throw.

rayman

 

[PhillyRube]

I have a modded Fenix P3D. Other than the weird square you get, it does great. Pure throw.....

 

[robert16]

iv had a mag with k.d aspheric upgrade , i sold this and got a tiablo A9 with aspheric upgrade i now have a ultrafire 501b with smooth reflector and aspheric lens for the money roughly 12£ im well happy...

 

[bluepilgrim]

I think reflectors are significantly better the lens for throw -- but the cost is that to get more throw you need a longer reflector (and light), while lens (aspheric or not), can be designed to be short.

 

[kramer5150]

IMHO they are fun to play around with and show off to others. But as a lighting tool I don't find them very practical for the previously mentioned reasons.

 

[dymonite69]

Are there any flashlights which combine a parabolic reflector to collimate the light coupled with a biconcave lens to precisely spread the beam?

 

[TorchBoy]

I think reflectors are significantly better the lens for throw -- but the cost is that to get more throw you need a longer reflector (and light), while lens (aspheric or not), can be designed to be short.

Yes, reflectors are significantly bettered by lenses for throw, because no matter how deep the reflector it still won't be capturing the highest intensity light coming from the LED. Lenses do that easily. Batwing profile LEDs might be different though.

 

[stallion2]

i wish aspherics were utilized more!!! i have aspheric heads for my DBS and Tiablo A9 but they aren't all that useful in any application besides long range. they just don't have an adequate range of adjustment (especially the DBS) to be useful for anything else. i'm hoping to try my A9 this year to do some spearing...i can adjust the beam to a wide enough angle that i THINK it may work well for spotting fish. now if more companies were doing something along the lines of Romisen and Coast then i think they could prove to be competitive options against reflectors. the two Romisen, single-cells i have are way more practical EDC's vs any of my other single-cell EDC's (and the Romisens were far less expensive).

Yes, reflectors are significantly bettered by lenses for throw, because no matter how deep the reflector it still won't be capturing the highest intensity light coming from the LED. Lenses do that easily. Batwing profile LEDs might be different though.

what on earth is a batwing profile LED?

 

[gcbryan]

I have one of the DX flood-to-throw lights. It's fun to play with and as far as I can tell from using it and reading reviews of Led Lenser and the new Krait from WolfEyes it seems to be in the same ballpark (and far cheaper).

It's still a weird light though. The flood is OK but it still has an abrupt cutoff. The spot is small and doesn't really light up much at a distance. In between it's interesting since it doesn't have that rectangular shape and it definitely goes where you point it but it's not as bright as it would be if it were not aspheric.

The odd thing to me is just that there are not really good versions of this light and even the more expensive versions presently available do't seem to be any better than the $10 versions.

 

[bluepilgrim]

Yes, reflectors are significantly bettered by lenses for throw, because no matter how deep the reflector it still won't be capturing the highest intensity light coming from the LED. Lenses do that easily. Batwing profile LEDs might be different though.

I was done in by my dyslexia/typos.
I said "I think reflectors are significantly better the lens for throw", which should have been 'I think reflectors are significantly better then lenses for throw'
Yes, you are right that the reflectors lose some light -- they need to be quite deep for best throw (and wide/big doesn't hurt either) -- but lenses also lose light, some by transmission loss, and also because they don't surround the LED completely and are not perfectly shaped. (Imagine a parabolic reflector that's 6" or a foot long.) But then, even if you lose some light the beam shape can still give you lots of throw. a good parabolic reflectors avoids spherical and chromatic abberation.

You do want a different LED for a reflector than lens as far as what direction it throws the light, though, I think -- and a LED is not a point source so that complicates things. A lens may be the most economical way to get throw, but I think a reflector will be better if done properly.

One problem is that a lense also acts as a 'crystal' to keep dirt out while a reflector would need a separate glass at the front for that.

Maybe the best bet would be a combination, something like catadioptric telescope, but the optics can get a bit complicated and expensive.

http://en.wikipedia.org/wiki/Catadioptric_system
A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses (dioptrics) and curved mirrors (catoptrics). Catadioptric combinations are used in focusing systems such as search lights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses.

Also see http://en.wikipedia.org/wiki/Mangin_mirror

There are two things to consider: how much light is caught to be directed, and then how it is directed. If a system projects a perfectly parallel beam then you get maximum throw, but if only 50% of the light was caught then it may well look dimmer than a less perfect beam which caught more of the light.

 

[TorchBoy]

stallion2, a batwing LED is also known as side-emitting. With a specially shaped primary optic it throws its light out sideways instead of forward, so they're ideally suited for reflectors because the reflector can actually capture/reflect the light instead of losing it out the front. Example pic.

I have one of the DX flood-to-throw lights. ...
The spot is small and doesn't really light up much at a distance. In between it's interesting since it doesn't have that rectangular shape and it definitely goes where you point it but it's not as bright as it would be if it were not aspheric.

I'm surprised you say that. First because I don't know how you know the focused spot would be brighter if it didn't have a lens. (I presume that's what you mean by "not aspheric.") Second because I have a couple of different models and they both throw very very well. When I got the first, a direct drive 3x AAA model, I found that it throws similarly to my 100 W (!) halogen spotlight... which I don't bother using any more. That thing has a huge reflector and emits lots of light, but they throw around the same. Why is yours not doing so well? What are you comparing it to?

bluepilgrim - um, "than" I'd believe, but you're now comparing catadioptric reflectors and parabolic reflectors 6-12" deep with aspherics. Is that what it takes? :ironic:

 

[gcbryan]

stallion2, a batwing LED is also known as side-emitting. With a specially shaped primary optic it throws its light out sideways instead of forward, so they're ideally suited for reflectors because the reflector can actually capture/reflect the light instead of losing it out the front. Example pic.


I'm surprised you say that. First because I don't know how you know the focused spot would be brighter if it didn't have a lens. (I presume that's what you mean by "not aspheric.") Second because I have a couple of different models and they both throw very very well. When I got the first, a direct drive 3x AAA model, I found that it throws similarly to my 100 W (!) halogen spotlight... which I don't bother using any more. That thing has a huge reflector and emits lots of light, but they throw around the same. Why is yours not doing so well? What are you comparing it to?

bluepilgrim - um, "than" I'd believe, but you're now comparing catadioptric reflectors and parabolic reflectors 6-12" deep with aspherics. Is that what it takes? :ironic:

I'm not saying that in its focused state that an aspheric isn't bright. I'm saying that in it's focused state it's so small that it's not that useful (IMO) and that as you unfocus the beam and get more toward a flood that it's not as bright as it would be were it not using an aspheric because the spill wouldn't be blocked and there wouldn't be whatever transmission inefficiencies there are (many aspherics are plastic and I would think that's not so efficient in it's own right).

In other words take a light with a reflector set up in a flood configuration and test the lumen output. Now keep everything else the same and replace the reflector with an aspheric lens in a flood configuration and I think the light setup with a reflector will output more lumens than the aspheric setup will.

 

[bluepilgrim]

stallion2, a batwing LED is also known as side-emitting. With a specially shaped primary optic it throws its light out sideways instead of forward, so they're ideally suited for reflectors
[...]
bluepilgrim - um, "than" I'd believe, but you're now comparing catadioptric reflectors and parabolic reflectors 6-12" deep with aspherics. Is that what it takes? :ironic:

Yes -- 'than' -- sometimes my linguistic neurons break up.

The optics I cut my teeth on were 'incoming' -- telescopes and such -- which are a bit different since you get only a small part of the light from the source. Focussing / collimating light emitters adds the aspect of grabbing as much of it as pssible to start. As far as have seen most flashlights with lens lets a fair bit of it escape to the sides.

If using a reflector, the emitter should be at the focal point, with the reflector picking up that light going off to the side, I suppose. Looking at my Romisen rc-29 I see the lens is about centimeter above the led, but I don't see how to get a lens shaped to go around the led and redirect that light going sideways out the front.

 

[csa]

I think current aspheric designs aren't particularly practical. The good optic designers are focusing on producing inexpensive general purpose TIR lenses. Unless some OEM decides to build throw-monster optics for some reason, you aren't going to see OEM aspheric solutions anytime soon.

 

[TorchBoy]

I'm not saying that in its focused state that an aspheric isn't bright. I'm saying that in it's focused state it's so small that it's not that useful (IMO)...

Ah. So you don't personally have a use for something that throws really well, like, say, possum hunting or playing spotlight with the kids. Fair enough. You don't have to use them.

bluepilgrim - ever tried using a telescope to throw?

 

[bluepilgrim]

[...]
bluepilgrim - ever tried using a telescope to throw?

I did once, many years ago, with an 8" newtonian I made. It was just a cheap 2D incandescent from a hardware store, and not bright, but when I put the bulb at the primary focus I could actually barely see a spot of light about 50 or 75 yards away -- although not bright enough to see anything by. I don't recommend carrying a 7 foot long flashlight around, though. :laughing:
But, then, most of the light was just scattered around with little of it making it to the main mirror.

Playing around with big reflectors is one my to-do projects, if I ever get to a round to it (or a parabolic to-it).

 

[utlgoa]

For the best Aspheric (type) flashlight you need to look no further than Led Lenser.

http://www.zweibrueder.com/

 

[dymonite69]

Here is an method to fabricate an accurate parabolic reflector. Once you have created the mold then it would be relatively simple to make a lightweight reflector.

The original idea is for a solar cooker but it could be scaled down for a flashlight.

Mechanical mathematician

 

[bluepilgrim]

Here is an method to fabricate an accurate parabolic reflector. [...]

Thanks. I'll have to look more carefully at that -- I'm not sure if it will do what I want, which is to make an accurate and very deep paroboloid. I was thinking make a flat negative template and rotate it on a form, maybe of plaster of paris, and then form a parabaloid made of foil around it. The end product would look something like a wine bottle in size.

I looked for how one would machine one if one had a lathe (sadly, I don't) but all the sites talk about formulas and NC controlled. I suspect there are other ways I haven't found. I would guess that there is some kind of simple jig that could be made to accurately fabricate/cut a paraboloid -- but I don't know what (yet).

One can make one's own lenses too -- I once made a few of glass for an eyepiece by grinding them on a drill press -- but they were spherical. I've played with plastic, which can be cut, but had a devilish time trying to polish them. Homemade optics is fun, but can be frustrating without good equipment.