There ya go. 
yes finally
back on topic, I just made an quick drawing following the advise of djozz :
from there it seems that not only my original idea will not work but also from a single point it will not work ?
Try this optics simulator, there's more of them on the internet and perhaps better ones, this one is nice and simple:
I am part of a DIY night vision building site… thats how i got into flashlights…
on that site, we make INFRARED ILLUMINATORS for our night vision.
the basic plan everyone ELSE uses on that site? a single lens, everyone says it has to be aspherical.
all the “new builds” all the members try? its basically just trying a differrent aspherical lens.
I wanted to try something DIFFERENT??
I build my IR illuminators, with 2,3 and 4 lenses… the first lens? its down INSIDE a p60 reflector, lol… the second lens? just outide the reflector… the 3rd and (sometimes) 4th lens? further out.
on my screen? I have taken pictures of my “well focused emitter” at up to and including over 800 yards… its DIM by that far? but, if i move the light and keep the scope still, i can SEE the light move.
mind you, this is with a 3-watt IR emitter… not some 15 watt super-duper modded job.
=
I had to solve the equations for 2 lenses, to get the focal length of the resultant lens assembly… to add a 3rd lens? i run the same equation, with the FIRST SET of lenses treated as one lens… and add the 3rd les as the second lens.
when i go “four lenses”… i treat the first 2 lenses as lens 1, and the second 2 lenses as lens 2.
also? my “last main lens” is the biggest diameter lens, and its smalled diameter than every other build (thy tend to go with ONE BIG ASPHERICAL)
none of my lenses are asphericals, lol… i came to the conclusion, that there is no compelling reason to use an aspherical. You can just as well use a plano-cpnvex lens(es) instead.
==
i broke a number of “rules” or “guidelines” with my design…
1) asphericals are not magical… i tend to use biconvex or plano convex. Diameter and focal length of the lens are the key specifications to a lens… not shape or type.
2) you cant use a lens with a reflector?? I do… i put the first (small) lens down INSIDE the p60 reflector.
3) you have to “black out” the reflector or inside of the head, or it ruins the beam… i found that the reflected light that goes into that FIRST lens down INSDE the smooth reflector? made the image brighter (can see further)
it was 6 to 9 month project… and i havent seen any other pictures or videos, or even a claim that anyone has seen their emitter focused up further away than mine.
I am slowly saving up for a metal lathe, because no one wants a IR ILLUMINATOR made out of plastic, lol… they want “all metal” in the field…lol
djozz is right you should be thinking in terms of magnification of an object. magnfication is completely dependent on the focal length of the lens or reflector surface incidence.
lens 1: similar to a TIR path. the problem is the distance of the aspheric to the source is so short, it will reduce the spill but not help the spot much.
lens 2, 3: are you trying to make a thrower or a laser? the initial profile of the beam is not going to be detectable at 100m let alone 10, again it’s the magnification at distances longer than the focal length which counts, so this adds nothing
i really like this presentation of flashlight optics here
Any thoughts on a freshnel lens
This one might fit into a Convoy S series
This one with a little bit of work might fit a 26.5mm P60 dropin
djozz, sedstar, islisis, WarHawk-AVG thank you for your input.
enjoyed pretty much the slides I know the major info before, but still its lot of information well putted and pretty much cover every thing, the data on nits even if little outdated are very informative.
and a good TIR looks like the first part of my system. interesting bit sound to me the dielectric coating reflector, what is that our ordinary cheap plastic reflectors? first time I hear about that high efficiency in reflector.
the simulator is lot of fun too, played a little today and it seems very useful. it save you a lot of time. I have downloaded some simple simulators for optics in my phone before, but seems difficult to operate. in contrast this is very easy and clean.
@sedstar, nice to hear you achieved good result. I am still learning and experimenting in this hobby of mine. but i have to say one thing, as far as i know u can skip aspherical in your night vision device and will not lose much because you use monochromatic light, but we in flashlight use white light most of the time and a spherical lens gave more precise focus if I am not mistaken. also a curbed surface reflect more light than a flat one near the source so it capture less light than an aspherical with the flat surface toward the source.
need some more time to experiment with simulator now cya
For compensating chromatic abberations, you don't need an aspheric, but an achromat (two lenses of different diffractive index glued together, compensating for different diffraction of different wavelengths), aspherics solve the focussing problem of spheric lenses that rays going via the side of the lens are focussed in another plane than rays going through the middle of the lens, you need an array of lenses to solve that without aspherics.
Nice one!
Anybody got a clue about their shipping costs (to Europe)?
member jspeybro (he's from Belgium) had some fresnel lenses for sale, he may still have some:
yes you are completely right, my mistake. I know it was to give a better focus but did nit geave enough importance the reasons behind. now that I read your coment, it make perfect sense.
Sorry to hijack some of your topic, but:
I came across that thread earlier.
You bought one, I believe.
But the one in the link seems to have (reatively) shorter focal length, i.e. larger diameter with F=15mm.
Shipping ruins it at $13.— 
link to the diy nv illuminator building forum? and link to your project?
QUOTE:“For compensating chromatic abberations, you don’t need an aspheric, but an achromat (two lenses of different diffractive index glued together, compensating for different diffraction of different wavelengths), aspherics solve the focussing problem of spheric lenses that rays going via the side of the lens are focussed in another plane than rays going through the middle of the lens, you need an array of lenses to solve that without aspherics.”
ANSWER: oh good sweet christ, i might finally be home, lmFao… is anyone remotely interested in the MATH?? I re-solved the “2 lens equation” to make it so i plug in the FL of both lenses, and the airgap between them… and it spits out the FL of the combined 2 lens system… I couldnt get a single person interested in the MATH, so i worked it into a easy “cookbook” equation plug in… IE, you can just add/subtract/multipy/divide on a calculator t get the result? no interest… I finally wrote a small piece of software to do it automatically? (click click click) and not one single builder on my other site was interested.
I kinda “gave up” and just went about my build myself…
===
the best source of lenses i had on hand at first? old gun scopes! the main objectives are almost always ACHROMATS. (they look like typical flint/crown affairs)
honestly? i buy the explanation(s) of why you have to use asphericals? But… we’re not IMAGING, we are just focusing some light beams. I mean, maybe this “registers” on some METER you guys all seem to use? But, with IR (mostly invisible) i dont have the luxury of using a METER… i only use one criteria “can i see the emitter image further than before?” if the answer is YES, its my new “best build” if its NO? it gets changed around…
since theres a tiny bit of interest, i might have to start another thread…
but, heres a LINK to pictures of my project, some of it anyways…
of main interest? the LITTLE illuminator? the cell phone pictures of the screen show before and after pictures using the TINY illuminator (2 cr123 batteries are for size reference)
bright as heck at 100 meters, 150 meters in the before/after photos, it poops out by 200 meters. BUT, its so tiny. its using 2 or 3 biconvex 3/4” diameter lenses. You guys will notice the p60 module (runs off of 12v nominal DC) taped onto the lens carrier (lens carrier by itself in second picture)
the third picture? is my BIG illuminator… the one i can “see” my focused emitter up to 800+ yards. In THAT one, the p60 IR module is tucked up inside the butt end… you can see 2 wires going in…. p60 module inside small copper coupling. Its a 3 watt device, so, overheating isnt a huge problem. The largest diameter lens is a 40mm or so achromat.
the BIG illuminator, with its fairly small 40mm main lens? outperforms 66 and 78mm asphericals… and really? how far would you expect to get with a 15mm diameter convex lens like the tiny illuminator uses?
it goes to efficiency
the last 2 pictures are before and after illumination pictures… note though, thats the TINY illuminator working, not the BIG one…
=
heres a picture of one of my night vision scope builds… this one is built inside of a “gutted” 4x32 regular gun scope…
the cell phone picture of the screen on th side of the unit? thats with no illumination, on a “no moon” night… the distance is ridiculous…
sedstar, I believe it was you who posted what a defocused IR laser looked like through night vision scope. Is it the lack of even illumination that makes the laser based illuminator a less worthy candidate?
Also, with regards to lens inside reflector, blacking out reflector, etc., it is assumed that the lens gets in the way of the reflector, or vice versa. What you are making with the reflector and the first lens is more akin to a TIR, in which light emitted “sideways” hits a reflective surface, while light emitted “forward” hits a refractive lens. I think this is why the accepted myth a while ago was that TIR is more efficient than reflectors because of magic. Is because TIR takes the light that would otherwise contribute to the spill, and redirects it into the hotspot.
I’ve always hated aspherics because they produce the best results easily, but are hard to understand with basic maths. Assuming point sources and all is fine, but knowing that real world sources are a plane, makes me think maybe the equation of the aspheric face’s curve somehow plays into concentration of light. Spherical lenses all have the same “shape,” so they ought to be easier to design in theory and bring out in practice. What are the lens equations you find most useful? I see that you say you did some work making equations or worksheets. Without spoon-feeding too much, if the equations only require knowing FL and distance measurements, it might be a nice workout for the ol’ headcheese
well, i started at th beginning, knowing about nothing… heres the readers digest version…
1) every lens has 2 main criteria… focal length (FL) and diameter… the stuff i worked with? not much else seemed to matter, at least with the basic math.
2) size of the projected well focused emitter? is entirely a function of the FL, and the size of the light source. if you have an ACCURATE measurement o the light source? an the focal length of the lens? you can fairly accurately predict the size of the projected emitter, at any give distance. (note: i am not 100% sure the “dome” does not SKEW the mathematical prediction, i think it magnifies it a little)
3) focal length is not a CONSTANT, it actually varies a great deal, depending on the distance to the target. If you pick up a “135mm FL lens”, if its an accurately described “spec”?? if you are aimig i against the WALL 3 feet away? you will measure a lot more than 135mm at that short distance… it will FALL to 135mm at “infinity”.
for this reason? if you pick up a random lens, say one you bought off the internet? and it did not have a “spec” for focal length? you cay just focus it at the wall, take a measurement, and proclaim it “thats the FL”
theres actually an short easy formula for that, where you enter the distance to the “target”, then it spits out the ACTUAL focal length.
4) a “simple” lens? which here would be something, like, say… a physically thin biconvex traditional lens? FL is measured from the MIDDLE of th edge, back to the source.
ONE problem with the internet “flashlight asphericals” that a bunch of sights are selling? is that many people measure from the REAR edge of the lens, back to teh source, and call THAT the focal length… compounding th problem is that many people aim it at the WALL across the room as the “target”… further compounding the problem.
=
all that aside? heres the basic formulae….
===
the FIRST equation is the most critical… but its useless in its given form. We want “f” (the resultant FL for the combined system…) by ITSELF on the left side of the equals sign, dont we? (yes, we do, lol)
i sat for a couple nights, using the super high technology that is a paper and a pencil… i just kept doing basic algebra, fairly at random, until i got closer and closer to getting “f” isolated like i wanted. Finally, i got the ratio of the gawd-d@mned airgap distance to product of focal lengths to “drop away” from all sides… which was a pain in the arse, but after about 30 or 60 “attempts” i finally got pay dirt.
made errors on several early “false successes”, then i finally got a solutio that worked, IE, i was able to go back thru, and plug in my answer, and everythnig was still equal.
i solved it several times, several different ways… and after getting the same resultant equation a couple times in a row, that checked out… i pronounced it “done”.
THAT produced a “cookbook” equation… IE, you just “plug in” the two focal lengths, and the airgap (even if zero airgap (touching…)) and it “spits out” the resulting focal length.
=
the SECOND equation is eminently useful, and as providence would favor the irish? it did not need solved… its a simple “plug in” and it spits out the “BFL” (back focal length), whhich is the distance from the middle edge of the rear thin lens, to the light source.
in other words, how close to the LED emitter th rear lens is (which is where the efficiency comes from)
after playinig “what if” with about a couple hundred “this lens FL, and THAT lens FL… what does THAT make?” I had the idea i should just write a little piece of software, to do this FOR ME, so i can just sit and play “what if” all night…
which is where these 2 screen shots came from…
you flashlight guys? you get a free pass on sm stuff i had to sweat about, lol… all YOU are concerned about, is “how does it LOOK?” and “can i SEE things at what range?”
then, you all sit around, ad offer “qualitative” things, like “beam quality”, and complain or compliment on tint and such…
in MY project? i have serious CONSTRAINTS on my emitter image… i am watching a SCREEN, which is hooked up to my sensor, which is receiving a IMAGE from a lens system. If the emitter size projected at distance is too BIG, i have wasted precious IR… if its too SMALL?? I can only see a tiny portion in the middle of the crosshairs of my view.
you ca mathematically describe a “field of view” wither thru a camera lens, or, thru a gun scope… many ways. You can specify the field of view by WIDTH and HEIGHT at a certain distance… or, you can express it as a DEGREE, or even as a radian measurement.
also, with a 3-9 variable power gun scope? this is dynamic… i have to be able to go from 13 degrees to 2 degrees, perhaps.
sized perfectly to the gun scope view.
=
before i worked out all the MATH, i was just “playing” with 2 lenses… it quickly gets frustrating, and you give up.
when you have run the MATH a coupe hundred times, you get a “feel” for what the two lenses are going to DO… and i began to not hav to run the math…
i can either set the front lens and find the BFL i need by inspection. OR, i can SET the BFL (distance to the light source) and move the front lens to focus.
or, i can set the airgap fixed… and move the light source to focus.
BUT, all this became possible only after getting familiar with the math.
==
this all ended up, wheere i realized i SHOULD be able to pick up random lenses… and MAKE my OWN “gun scope” or “camera lens”…
and, this worked out too.
I also take camera lenses APART, and add or subtract lenses t the camera lens… to adjust the FL of the lens, and also to set the “F” number (light transmissionn) of the camera lens to where i need it to be.
too little light transmission, no night vision… too MUCH light, or, off axis light nearby? and i “wash out” and its unuseable…
here’s me with the japanses lens system salvaged off of an old camcorder, and resetting it to focus up on a sensor…
===
that was just an early “proof of concept” for the later “hand held night vision spotter” unit…
==
heres some before and after and “working” photos of the little screen wth a cell phone. MIND you? this is a low res cell phone pic, of a little screen… what i see in “real life” is MUCH crisper and more detailed. Its like watching cable TV channel, lol…
150 meters… control shot (no illumination)…
same 150 meters, with illumination…
same 150 meters… defocused for wider more even illumination…
heres a “line of sight map” i made, because i crushed my distance my laser ragefinder will work at… only way could determine true distance… (and? this is flat distance on the map… TRUE distance is greater, because i’m up on a hill, and the angle makes it even further… cosine of the angle, is the adjacent divided by the hypotenuse… remember “chief SohCahToa” from Trigonometry class? lol… the true distance is the hypotenuse… the adjacent is the map distance…
and heres an image, of the far river bank, 800+ meters… no moon out. pitch black. (light has been defocused for even illumination)
heres about 350+ yards… control shot, no illumination…
same view, with illumination…
heres a “practical” view… of a live GAME ANIMAL… so you can get a feel for if it “works in real life” or not, lol…
heres the updated handheld spotter unit… this puppy is so sensitive? in most situations, it doesnt need ANY ir illumination, heh heh… its about as far as the eye can see in the daytime? except at NIGHT when there is NO MOON out at all, ha ha… i took a real camera lens apart, and added a lens in the rear of the unit, behind the iris mechanism… and adjusted the focal length to suit my needs.
and, heres the “big” illumniator, mounted on a gun scope… prototype naturally… needs to be metal lathe’d out, and a real windage/elevation mount added… and thats not a “real” gun scope… thats a night vision scope, built completely inside what was formerly a gun scope… THIS is the unit that you saw 800+ yards across the river to the far riverbank, on a moonless night in pitch black…
lastly? (finally, whew you say, the end?) heres what i mean by “pitch back” with no moon out… this is what “across the river” looks like, without night vision…
i spent 45 minutes, putting in th photobucket links to the images!
not ONE showed up!
i could just put my FIST thru my laptop screen right now!
I always wanted to try that with a cast iron pipe, see if I could boil water…think zombie apocalypse diy boiler/hot water heater
What worked for met:
on the Photobucket page klick on “direkt Link” when your Picture is showed
copy / paste here and add a >> ! << before and after the Link