How do these work?

[LEDagent]

After pondering the different ways light can be focused, i haven't seen too often the use of projector lenses.

I've been inspired to think more about how the Megaray optics work and....if I can make my own.

So I start looking up projector lenses to see if I can get any more ideas on how these lenses can focus light.

From my brief study, it seems like the main goal for projectors is to project an image larger than it's original source (duh!). However HOW do i get the projector to focus the light into a spot (like the Megaray) rather than a flood (to make an image)?

I did more studying and it looks like there are some car manufacturers using projector type methods in their headlights. I came across some stuff on eBay called HID Projector lenses, which usually come off of high end cars like BMW.

This reflector/lens combination projects a wide beam for driving and somehow disperses it evenly towards the ground with a sharp cut-off so not to blind other motorists.

My guess on how they do this is by using an oval shaped reflector (as upposed to circle) to make the wide beam, then they block half of the reflector to project the sharp cutoff, and then they use a lens to project the light.

1) Why do they use a projector lens rather than a reflector? The reflector is already there to project and shape the light forward...it sounds redundant to me. Is the lens somehow shaping the beam even more?

2) how can i get the beam to be less like a driving beam pattern to a spot using this same optics setup?

Isn't it possible? I mean, the Megaray kind of uses something like this; but i'm sure it has even fancier stuff going on in there.

I'm getting tired of finding a good host for an HID mod that can focus the light tightly. It's easy to go the Thor or Lightforce or Spotlight direction, but even those project the artifacts that the HID bulbs have (bond wires). Projectors output the smoothest, prettiest beams of light that i know of. When focused down enoegh, they look just like the Megaray. Compare that too with the Maxabeam which uses a 10" reflector.

The Megaray, however, uses a short-arc xenon. This has a small point of light as uppose to the D2R bulbs which have a larger point of light. Would the projection lens need to be even larger than the ones found on BMW headlights?


I'm sorry for all the questions, the structure, and word flow of this post. I'm writing this at 5:45AM after a few hours of researching this stuff...and no sleep...yet.

I go sleep now...and dream of flashlights.

 

[PeterB]

Question 1:
The bmw lights use to my knowledge an eliptical reflector. With this reflector you focus the light to an intermediate immage and a lens projects this image to a parallel beam. The advantage is, that you can place an aperture at the intermediate focus point, which defines precisely the beam pattern.

Question 2:
Maybe you could remove the aperture?

 

[LEDagent]

Peter,

If i use an apature to to shape the beam going through the eliptical reflector, won't I be just wasting a lot of light that isn't being past through the apature hole?

If i remove the apature, i'm thinking that i'll be getting a large flood like beam. I wonder how much distance from the reflector i would need to get it down to pencil beam light. If i could cover the space between the reflector and eliptical reflector with a reflective inner tubing so not to lose any light, I wonder if i could achieve the same effect as the Megaray.

I'm sure the Megaray however has a different optical setup with magnifiers, mirrors, and lenses.

 

[Steelwolf]

To focus your light source to a thin, tight beam, you should not be looking at flashlights. Instead, look to telescopes.

Over a long enough distance, light from a point source, such as a distant star, will tend towards parallel rays. This is then focused to a point by the telescope. In an el cheapo device, this would be accomplished by just 2 lenses. You can get the same effect by just using 2 magnifying glasses and varying the distance between them and your eye to get a clear image.

What you want to do is reverse the direction of light travel, but with essentially the same path. The biggest difficulty is that with a typical light source, such as our HID bulbs, very little of the light produced actually travels in the correct direction (ie towards the focusing lens).

Hence, the first order of business is to find a reflector that will collect the light and send it in the correct general direction. Something like those from SureFire would probably be best, but even the Mag stuff will work. This takes the place of the first lens. Next, a lens in front of the bulb/reflector setup will focus the light to a parallel beam. You just need to be able to adjust the distance of the lens from the reflector to be able to focus the beam.

In the distance between the reflector and the lens, the light beam will diverge slightly. This may cause some losses if your lens isn't large enough to capture the spill. You could put a highly reflective tunnel to channel the light, but of course, since the light rays are now bouncing off the walls of the tunnel, they are not reaching the lens at the correct angle. This will result in a brighter side-spill, but may detract from the effect of a tightly focused light.

In fact, I had a chance to play with a theatre spotlight and the internal workings where pretty much what I described. It had a reflector and a main lens. In between, it had a second lens to allow focusing of the light to a tight circle, since the lamp array and the main lens couldn't move. It had an aperture to tighten the beam (with resultant loss in overall light output). The innards were painted a matte black so that there would be no stray light bouncing off the inner walls and ruining the effect of the tightly collimated beam.

Hope that helps you. These are also tired ramblings as it is 3am here and I am in need of sleep. /ubbthreads/images/graemlins/smile.gif

 

[LEDagent]

OH gosh i never thought about telescope optics. But now it sounds like a big project...not just money wise, but size too.

To focus an HID D2R bulb with a reflector like you mentioned above would require a big reflector, like at least 4" maybe up to 6" or 8". And then after that i think you would need an even larger lens to capture all the light. Lenses aren't cheap either.

I've been to a few theater productions but there was one production that really amazed me. It was Cats. They were here in San Diego in the Escondido Performing Arts Theater a few years ago. THe show was great...but the FOLLOW SPOT was AWSOME. It was a pretty bluish white while it cut through the theater darkness. You could see the beam through the air. These don't use HID right? I think this one uses an HMI bulb. I hear these are super bright. Would i essentially need something that big to focus an HID light?

 

[jamesraykenney]

One night while my astronomy club(ASSET) was out observing, we had someone attack us with a q-beam(or something like that)from a LONG way away.

I pulled out my Surfire 9P(I think... the 3 123cell black one) which just happens to have almost exactly a 1.25 inch head(good telescops use 1.25 inch eyepieces[or bigger],) and put it into the focuser(the thing that holds the eyepiece)of a 12-18 inch Newtonion reflector...You would not belive the been that thing put out!!! They stopped shining the q-beam at us /ubbthreads/images/graemlins/crackup.gif

 

[Sachsenwald]

Hmmm....... hope i`ve got it. I´ve rendered a simple graphic, is this the right way to produce a tight parallel beam like the megaray?

 

[Draco_Americanus]

The theater do indeed use a HMI short arc xenon lamp in the high end lights, sadly to get a 35 watt metal halide to focus like that you would indeed need something that large because of the arc length.
The hella projector style hid lights for cars make a great looking beam but you are totaly correct on them being more of a flood light. I have a style they called DE that are claimed to be the smallest D2S projector style lights made. They are totaly coated in reflective materal on the insides and are dang bright but they have a clear class cover rather then a normal lens and do indeed project a powerfull main beam but the sidespill is realy insane and you can see the return wire shadow as well. They a great for a quad but unless you wish to get shot I would not recomend them for a car. hella's micro DE /ubbthreads/images/graemlins/cool.gif

 

[eebowler]

Wouldn't a lens in front of a reflector and bulb in effect be projecting an image of the light source foward at some distance? Would this pose a problem if the filament of the bulb is on the long side?

 

[Leonard]

Megaray uses as small an object(glowing plasma ball) as possible -under 1mm as a point source which then is captured by the reflector which is a positive lens (convex). The light is then directed through a Galilean telescope which acts to minimise angular dispersion giving you the tight beam that is so characteristic of Megaray. it must also be noted that the reflector must be as small as possible to minimise the three main areas of optical aberrations-coma, astigmatism and spherical aberration. These cause the rays to spread out and "get lost". The bigger the reflector the worse the aberrations and the more uncontrollable light becomes. Remember the ultimate usage of the light is irradiance-how much power (joules/sec) falls on the target. Another consideration is the focal length of the illuminator-the longer the better and the Galilean telescope serves to increase the focal length and in the case of the Megaray by a factor of 4. It has been mentioned as to what is focussed and here one must look at the field stop and the aperture stop. In Megaray for the focussed beam it is the field stop and when defocussed the aperture stop. Hope this all helps to the understanding of Megaray with the application of first order or Gaussian optics. Incidentally Megaray is the only unit in the world that we know of that uses a Galilean telescope for enhanced optics and until the others go this route they will never be able to compete. These are the immutable laws of physics.

 

[Leonard]

Dear Sachsenwald,
The drawing thatyou have depicted is optically incorrect and does not work the way you have drawn it. In fact it works the other way round. In your system the light rays will converge to a point when leaving the front lens and will not emerge as parallel rays. You must take into account that the reflector is a convex or positive lens.

 

[Leonard]

The best and only way to get a tight collimated beam with minimum beam divergence like Megaray is to go for the very smallest objective and the longest possible effective focal length. This can only be done with a SMALL (under 1mm) object and the SMALLEST possible reflector and then passing the rays through a Galilean telescope. And this is exactly what Megaray does and nobody else.

 

[lasercrazy]

Does anyone know how much the new version of the megaray costs?
I would assume it's at least $5,000.

 

[LEDagent]

Somewhere around there. After $2000 for a flashlight i stop counting. /ubbthreads/images/graemlins/grin.gif

Thanks Leonard for such a full description of these optics.

 

[Sway]

Leonard,

Welcome to CPF and thanks for the insight on how the Megaray works /ubbthreads/images/graemlins/thumbsup.gif

Now if I could just get my hands on one /ubbthreads/images/graemlins/grin.gif

Later
Sway

 

[Sachsenwald]

Dear Leonard,

thanks for this detailed view how the megaray works. I cant stand, i just was drawing a new graphic, hope this is the "basic" princip to get a thigt beam. I know, the lenses and the reflector are not in the right proportion but i think this should be the right princip.

Christoph

 

[Leonard]

Dear Sachsenwald,
This is starting to look better but why put a biconcave lens between the reflector (which is in itself a plano convex or positive lens)and the concave lens? If you leave this out and get your focal lengths right then voila you have a Galilean telescope and have now done what Megaray is doing. Do a ray trace of the above-it is very revealing as to why you must go this route. In essence what you are doing is extending the effective focal length of the black box and in so doing you reduce the angular dispersion of the beam giving a tight collimated result. Remember there are only 2 ways for tightness (1) extending the focal length of the black box and (2) reducing the object to a point source. Everything that you do in the system must be geared to this end. Of course I have not mentioned optical abberations of which there are 3 main types (I am excluding refraction) 1.coma, 2. astigmatism 3 spherical abberation. These abberations occur in the opticl system in the lenses and once again the Galilean telescope minimises these. I want to point out that the measurements here are sub wavelength the very smallest variation in say the reflector can cause major and I mean major light dispersion (can be up to 50%and more). So be careful in your design. To help minimise spherical aberration and coma you must use the SMALLEST reflector possible and then pass the rays through high quality carefully designed optical lenses. See why Megaray costs what it does.Most people just do not understand the optics and design that must go into a good system .
Regards,
Leonard

 

[Leonard]

Sorry I meant biconvex

 

[Sachsenwald]

Dear Leonard,

you are right, now i´m understanding why the MR costs what it cost, i was looking around for some prices for high quality non-reflecting lenses and these are huge (still waiting for the price-list from jena-optics /ubbthreads/images/graemlins/icon3.gif )

Christoph

 

[cheesehead]

But with respect to "throw" is an optical system any better? Certainly the de-focusing seems to throw a much nicer pattern (no donut hole), but overall throw I can't imagine would be any better. Looking at the Superlights on Kenshiro post, the maxabeam with it's lower wattage short arc still throws a very nice spot, while the MR looks a little more diffuse.

Just trying to figure out which light to ask for my birthday present, (well, ok, in my dreams).

cheese