How to make the best single lens zoomie... (alternate title? we finally have a complete math model)

Flashlight Modding and DIY Parts
1

Look guys, i am not “here” because i was initially all that interested in visible zoomie flashlights. I am “here” initially? for a much more selfish reason. I come from a night vision site, and we all “fanned out” and hit the flashlight sites? Because we were building “IR zoomies” and we needed more at the time… every time i asked everyone there “where’s the math model?” I got a lot of static.

basically? here was their site wide strategy to build a better single lens zoomie (IR, but still) and its going to look VERY familiar to you guys strategy… up until now.

1) “hey guys… check out this cool lens i found and bought!”
2) “well, build an illuminator and lets test it !”
3) a build would occur, and it would be trialed, and the results shown
4) go back to step #1…

Now? right off the bat… nothing WRONG with this strategy, but, its a SLOW strategy. Its highly inefficient. It “works” and it provides slow, incremental success? But… without a complete math model? its lacking.

I at the time? knew nothing about the “camera math”, and i had to start at ground zero soaking as much of it up as i could. I did… this helped me with the IMAGING side of night vision. I had to understand how camera lenses worked, since we use them in night vision building.

but… on our ILLUMINATOR side of things? we were flying blind (night vision joke, lol).

I went out and found the math information that suddenly allowed me to make COMPOUND lenses for IMAGING, and it suddenly allowed me to do things i wanted to do, that were useful for imaging in night vision. THAT “camera work” i will call it? taught me one thing… F NUMBER is the measure of how much light a lens can transmit… period. Compound imaging lens, single lens imaging system… did not matter.

there is no other “measure” of how much light a lens can “throw” for you in imaging. AND i realized imaging and illuminating with lenses? Are the same thing… think about it… let that sink in.

For some ungodly reason, that i never COULD fathom? everyone thinks (erroneously) that “F numbers are for cameras” and “throw” is for illuminators. I dont know “how” and i dont know “why”, but… somehow and some way i cant imagine? Someone came up with the idea that:

“diameter equals throw”

and

“focal length only affects beamshape! it doesnt affect throw!”

these statements are PARTIALLY correct, at best, and thats being as “charitable” as i can. At WORST? I dont know “why” and i really dont care at this point? For some reason i cant fathom… people that dont really “do” any math whatsoever, learn nothing except tp repeat those 2 phrases like a parrot? and they think they now have memorized some kind of “sage knowledge” that really doesnt mean much.

which really wouldn’t bug me half as much the last couple years? Except every time i try to STATE something useful in public, on any post about how lenses work? A never ending stream of people come into my thread and repeat those 2 phrases like a parrot? and they “correct me” like a school teacher is correcting a young student… with some “air” of knowledge, that is misleading at best, and “wrong” at worst.

I am very, very sorry to report? You guys favorite “two catchphrases” are mathematically incorrect. The figures do not lie. Equations show EQUALITY between two things? And unless and until you show me different equations that state something else? I can mathematically prove what i say.

The HUGE dis-service you are doing? In repeating these catch-phrases without understanding the complete system? Is newbs are going off “half cocked” that simply learn those 2 phrases, and think they know something they really do not. Again, i am sorry to shock you, but, i can prove what i say.

They are an incomplete description of the system.

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i am “here” originally for the very selfish reason, that i needed to learn how to fabricate MY STUFF in MY FIELD out of solid metal… i needed to learn to fabricate out of metal, and to perform basic machining, and now to cast my own aluminum stock and be able to BUILD my prototypes out of solid metal? so that they are useful to people. Better prototypes build out of empty tubes of deodorant and cardboard tubes? dont work well in the field, when mounted on high power rifles in the rain and snow, lol…

my night vision “stuff” is similar in size and shape and aluminum content to a flashlight… if you squint your eyes without your glasses on? they are similar looking devices. Metal tubes, machined aluminum… and camera lenses on the night vision units… and lenses in front of LED emitters for the illuminators.

I feel GUILTY i am here for a selfish reason? TAKING from your site, and not having anything else useful to give you back in return for what i took. I now have a few keys on my keyring? That are the keys to the kingdom… and i am jingling them in my pocket.

i found a coup[le years ago? a “white paper” as i call it… an engineering paper from EDMUNDS OPTICS? That is entitled “Prototyping illumination systems from stock components”. It describes, in mathematical detail? EVERYthing to do with a single lens zoomie, except in mathematical terms.

in years? no one would read it… if they did? they invariably said “i cant do it all”. I had to do it myself… the first half of the engineering paper? concerns “one lens” illumination and provides a complete math model of it. The second part? concerns dual lens illuminators, which is what concerns me.

i finally worked completely thru the whole thing. I might not be 100% correct in my understanding of the multiple lens system? BUT, the important thing? Is that i had to be able to completely work thru the math of the SINGLE LENS system, to have a chance at my part.

if you want to shock your meter with a single lens zoomie? This is the best way to understand it. I can now answer questions like “what lens specs, will capture all the light from a emitter?” with mathematical certainty. with terms and definitions that actually MEAN SOMETHING, and are not “half truths” that mislead everyone.

there was once a guy around in flashlights? some Dr. Hoozits? i dont remember his name… lets call him “god” for lack of a better term for it… well, GOD doesnt talk to you anymore. I am here, and until you get “better”? you’re stuck with me. Because i worked thru the math, and am in a position to explain the truth.

lens DIAMETER is truly a wonderful thing? But, its only half the battle. Ignoring the focal length? The way your “favorite catch phrase” says? is incorrect. I want to put that to rest. Quit WORSHIPPING one half of the complete picture? and IGNORING the other half of the picture. You need both.

Now, i developed a “love” for flashaholicism in the couple years i spent here “incubating” my ability to BUILD and do basic MACHINING. When i say i am “going back” to my night vision site? I am not “leaving” but i am going to be spending 90 percent of my time there, and in a little while all my money and energy building my night vision proptotypes… shifting back to where i came from.

in the course of doing all this? i have finally “worked thru” the engineering paper for the first time, and i know what the math means in practical terms. If you dont believe me? whatever. But, i am your “bridge” between:

1) the engineers at edmunds optics, who spelled it ALL out in a math paper?

and

2) practical building and testing, and arguing with incomplete ideas and downright misleading terms and “laws” that do not exist

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heres whats basically going on….

pick up any lens? any single lens? it has 2 properties… focal length, and diameter. the relationship of focal length and diameter to each other? the ratio? is called “f number”. it is quite simply FL divided by DIAMETER.

both are EQUALLY important. To state that “diameter gives you throw” is a half-truth and misleading, it is quite simply… mathematically incorrect.

NOTHING ELSE enters into a lenses ability to transmit “more light” than the f-number. Nothing. Now, CAMERA guys already know this to be true… it is the only figure of merit for “how bright of an image” a camera lens will reproduce on film or a camera digital sensor.

now, when i first encountered the engineering paper? f-number isnt mentioned anywhere in it. I allowed that to “throw me” for along time. Everything is instead stated in terms of “numerical aperture” and trigonometric functions. Where was my precious F-number? It was RIGHT THERE, and it was staring me in the FACE… my f-number was hiding under an assumed name, with a fake ID and a funny nose and moustache glasses.

numerical aperture is the same thing as f-number. Its just STATED in a different FORM.

I spent the better part of two YEARS, trying to combine equations into one set of “master equations”… simply because i had missed this fundamental concept. Quite simply? i missed the forest for the trees. I was at the TOP of the “problem”… and the simple answer was at the BOTTOM of the problem.

NOW in hindsight? i feel very stupid, but, an answer is stil the answer, no matter how long it took me to find it.

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we all already know that every LED emitter has an “emission angle”. Its stated on the datasheet as the half-intensity angle. Its simply the ANGLE that the light spraying out contains “half” of the intensity. Its the “cream” contained in the raw milk out of the cows udder.

this ANGLE is critical. If you want a “best single lens zoomie”? you need a lens, whose diameter AND FOCAL LENGTH, create at least this angle. If you only go looking for diameter? mistakenly thinking that “diameter = throw”?? you are chasing your own tail. you will never catch your own tail, ask any dog or cat that spends a lot of time doing it.

the WHOLE PAPER, concerns itself with ANGLES. and not… much… else.

someone told me in another thread? “well, thats sort of true, but… the laws of ‘absolute throw’ says…” and there is no such law.

now, let me get this out right now. you guys’s “surface intensity” stuff? you use to estimate how many moonbats are getting thru the lens? to create theoretical “meter numbers”? which you then later measure, and see how it all does? its TRUE… but the brightness of the LED emitter, has NOTHING to do with the lens’s ability to transmit light.

to a CAMERA guy? focusing an image onto film or sensor? he will say the F-number represents this, and that a lower f-number will transmit a brighter image. period. F-number is simply the ratio of diameter and focal length.

to the OPTICAL ENGINEERS at edmunds optics? They state “sine and cosine” functions, and state them as “numerical aperture” and work out ALL the equations that govern and control this? that way. NUMERICAL APERTURE = FOCAL LENGTH, they are the same thing, stated in a different FORM not instantly recognizeable. Once again? diameter AND focal length? are both inextricably linked.

now, if you draw a simple cartoon lens on graph paper? and shoot a line back thru the center? and mark a SPOT to scale that is the location of what we call the “focal length”? and take straight lines from the top and bottom edges of the lens straight back to that point? where they all 3 intersect? thats the “focal point”. and you will see an ANGLE FORMED.

this critical ANGLE is everything. you CAN make the angle bigger, to accept more light form the LED, by increasing the diameter of the lens… you now have an angle, big deal? that angle is everyting.

you see, you already have an ANGLE stated on the LED data sheet? you need a single lens, with that angle or greater, to capture all the light. The graph paper picture, if drawn to scale? lets you DRAW that angle accurately. Match or beat that angle? capture more light.

now, if you want a throwy zoomie? you increase the focal length, which decreases this angle the lens captures. you now have to increase lens diameter to re-capture this critical angle… and you run out of dance floor. what to do?

simple… the easy math that calculates the NEW focal length, when combining two lenses to make one new compound lens? allow you to create a lens out of thin air, that will MEET your expectations of this critical angle.

the FLIP SIDE of this picture? is that FOCAL LENGTH and focal length alone? control the SIZE of your projected emitter at a specific distance. a smaller emitter at distance is “brighter” and doesnt run out of legs at longer distance. BUT youre up against the “design dance” of finding a lens with enough diameter (and focal length) that meets your requirements for this thrower.

NOW then… lets look at a easy and practical application of this principle, now that we know it….

1) the LED emits a critical ANGLE, we need to meet or beat that critical cngle.
2) you draw an accurate to scale drawing of the lens diameter and focal length? to easily see this angle the lens accepts
3) for a thrower? you will quickly want to paint an emitter thats smaller and more useful at distance than any lens you can buy or find…
4) simply combine two lenses of higher and equal focal length to create this angle

example…. a waiven coller over an xpg2? increases the brightness of the LED under it once its set and working properly… asd it has an emission escape angle of plus minus 30 degrees, 60 degrees angle in total.

draw to scale a line drawing of the lens you are considering, you will see an angle coming out of the focal point.

if you cant find a lens thats wide enough with the focal length you need? you simply grab two lenses of higher focal length and let them combine to produce this new lens that MEETS or EXCEEDS your angle requirement.

when you run out of “dance floor”? simply combine two lenses to create a compound lens that yields what you want and need.

this “angle” can also be represented (very handily, i might add…) with the F NUMBER of the single lens…

if you want a floody zoomie? fine… you meet or exceed that angle, which is to say “find a lens with the correct or lower f-number”, you will capture that angle, and both you and your meter will be happy.

if you want a thrower zoomie? with more legs? simply find a lens with the same angle (f number) that captures that critical angle, and has the focal length that “paints” the smaller size emitter you want…

if you cant find it? you already KNOW the f-number you are looking for? simply take 2 lenses of higher FL and slap them together to lower the FL of the new compound lens, which keeps the DIAMETER of the bigger lenses, and now your new lens you made out of 2? has the same diameter, and a much lower focal length… effectively creating your critical angle you need.

the following catch phrase needs to die…

“diameter = throw” because its a half truth and incorrect

“only diameter gives more throw” is a half-truth at best, and lets people memorize a rule that misleads them.

you start to use these ANGLES like i am describing them? your gonna see meter readings go up. when you cant find a lens with the right f-number that matches your line drawing at the focal length you want for your thrower? simply create the proper f-number out of two higher FL lenses touching to make it out of thin air.

and “all” that is going on with the pre-collimated dual lens zoomie? is using two lenses, to create a ratio of the focal lengths, that creates this critical angle. (which at higer FLs, is impossible any other way)

i say “all” because it sounds a lot easier than it really is… but, thats skinning another different cat…

=

stated another way?

1) you already HAVE a zoomie lens, and you like the size emitter it paints at 100 yards? and its a certain focal length. doesnt matter what it is. Lets say its a 50mm diameter lens, with a 100mm focal length. (thats F=2.0)

2) your line drawing show you, that you “need” the critical angle that comes out to F=1.0 or better.

3) now you “need” the same focal length to keep the emitter that size you like… 100mm FL…. you now “need” a 100mm diameter lens with 100mm FL? and you might not find one…

4) you CAN FIND a 100mm diameter lens, with a 200mm focal length… you simply buy two of them, and place them touching, and you have now “created” a lens with the diameter and focal length you needed.

5) why is this useful? simple… bigger diameter lenses are readily and cheaply available? but, with too high of a focal length that raises the f-number… you put two of them together to lower the F-number to hit the critical angle the LED is emitting? watch how happy your meter gets…

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ignore me? at your own peril, and keep doing what you have been doing… i am telling you the sheer naked “complete” truth…

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Here, i am going to create a few CAD drawings, that illustrate this whole concept… i think once you look at them? and compare them to my text above? a few light bulbs are going to “see it” and light up? and the rest will flow from there…

example: what lens will capture the light from an xpg-2 under a properly set and working waiven collar? without inefficiency? The waiven collar has an emission angle of 60 degrees full angle, or plus minus 30 degrees

the “answer” is N_O_T “what diameter lens do i need”… no, the CORRECT answer is “what F NUMBER of lens is required to do this job”

this picture illustrates several lenses, ALL of which transmit the SAME amount of light… they ALL have the same F Number… they all have the same “numerical aperture”… they all capture the same “angle”…

now, everyone keeps saying “F number means nothing”, and it means EVERYTHING… when i say “the F number of THAT lens is lower, it will do better”?? i know exactly what i am saying, and someone always wades into it, and says “something” that indicates what i am saying is not 100 percent correct… and i know i AM correct.

please notice, that each of these lenses? has the same F number, because when you divide these diameters and focal lengths out? they will all yield the same RATIO. because they all have he same ANGLE of CAPTURE. N_O_T_H_I_N_G except “F number” describes how much light the lens will put thru it. I dont care of you are imaging a fart lit on fire out of a cows @$$ onto a film camera, or, say… projecting a beam of light from an emitter

please note that your “throw calculations” about surface illumination? have nothing to do with the ANGLE of the lens that it can capture… the lens does not CARE what YOU want to put thru it… you HIT this critical angle you are looking for? you make your meter happy.

you COULD describe this critical angle? as “numerical aperture”, but, if you look up “what numerical aperture IS” on wikipedia? you will see clearly that numerical aperture is the same exact thing as F-number… its just STATED in terms of a trigonometric function.

the entire engineering paper is worked out in terms of NA, but… thats just the FORM they like to use to make their equations smaller and easier to work with.

to ME? F number is “all there is” to describe “which lens is better”… to the engineers at edmunds optics? NA (numerical aperture, stated in terms of trigonometric function) is all there is to describe which lens is “better” but…

F-number EQUALS “n.a.”

period. end of story. done.

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NOW… it is true and correct to say that a larger diameter lens “throws better”, but… only if it has low enough of a focal length SUCH THAT the f-number is LOWER. I am telling you? just because one lens has a larger diameter? does NOT, under any circumstances, let it transmit “more light” to your meter? unless the ratio of diameter to focal length comes out to… a lower F-number.

this… this isnt my “pet theory” that needs “proven” with a ray trace that may or may not illustrate it… this is well proven, cold hard mathematical FACTS. If your ray trace does not illustrate this concept? You need a better ray trace, sorry. This honestly isnt open to debate, this is the very foundation of optics.

and? the next person that says “focal length only changes beam shape… only diameter increases ‘throw’ ” needs beat down with a very heavy asphere in a strong sock, until they quit spouting off false information.

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now, focal length does affect “beam shape”, this is true as well. two lenses with the same focal length? will “paint” the same size emitter at the same distance. Period.

Mr endermans ray traces? when he tried to “model” two lenses touching? here’s what he didnt do…

1) ray trace of a single lens, 100mm diameter, “whatever” focal length (lens radius?)

2) ray trace, of two of the same 100mm diameter, same FL (radius) touching? THEY NEED TO BE HALF AS CLOSE to the emitter, because the focal length just got cut in half.

you ray trace THAT? you will see this demonstrated, hands down.

if you build around the ANGLE, then compare lenses based on their F-number?? you are comparing apples to apples…. any diameter and any focal length lens you consider? will divide out to a certain “F number” to allow you to compare them.

there simply IS NO “but you see, the law of absolute throw says…” because such law is made up and dosnt exist.

=

if you bother to read the engineering paper? you will see its ALL “numerical apertures” usd to compare lenses… you will also quickly see that “numerical aperture” is the exact same thing as F NUMBER.

its not “one way” of looking at things… its the ‘ONLY WAY’.

now, if you want a thrower zoomie? and you want (hell, NEED) a certain f-number to get the proper angle of capture? draw a damn picture of the lens, keep the diameter and focal length to scale… and see if it has the angle you want… nothing else will work the way you want it to.

a bigger diameter of lens? will NOT automatically “out throw” a lens of smaller diameter… the smaller diameter of lens WILL out-throw the larger diameter lens? if it has a lower F-number… period.

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lower f-number? = happier meter readings. there is no “but you have to consider…” because there is nothing beyond f-number that conveys any useful information…

when you look into the pre-collimator system mathematically? you are simply creating a ratio of the two lenses focal length, to CREATE the “numerical aperture” you might not be able to get with any single lens… IE, you are creating the F NUMBER you are looking for… IE, you are making that critical angle from the drawing.

=

anyone that says anything else? is either lying to you, or, doesnt understand what the engineers at edmund optics have to say on the matter… and when you slap two big diameter lenses together to make one new compound lens out of them?? you have effectively cut the F-NUMBER in H-A-L-F… use this KEY design ability to your advantage…

(move the ray trace BACK half as close as the original one lens ray trace? see how many rays you capture…)

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sedstar, I love your attitude, love your enthusiasm, love your can-do-figure-it-out nature, love that you bought a few thousand XP-G’s and sold them to us for $0.20, really love that you made your own freaking FOUNDRY to make what will likely be the MOST scratch-built light BLF has ever seen. But damn if your stream-of-consciousness writing style isn’t hard to digest, lol! My mental image of you is definitely “mad scientist” :smiling_imp:

I’m still working through both of your posts, but do you have a link to that Edmunds Optics paper? I’d like to read it.

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https://www.edmundoptics.com/globalassets/resources/articles/prototyping-illumination-systems-with-stock-optical-components-en.pdf

everything is on “page one”… the later pages are all light pipes and micro lens arrays that dont concern us here…

and remember, “numerical aperture” can be replaced with “f-number”… its the SAME THING stated differently…

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You can see in my ray traces that one lens of X focal length was at distance X from the LED, while two lenses as close together as possible, also X focal length each, were at X/2 distance from the LED.

So yes they were half as close as you claim.
The focal length of the single lens was ~124mm iirc.
When the two lenses were together, the point in the middle of the two was about half of that.

7

creating a light engine with a smaller emitter? putting more amps thru it by heatsinking it better? does well indeed create more light, and does create a better light engine… but… the F-number of the lens? controls how efficiently you are going to throw it downrange, irrespective of diameter and irrespective of focal length.

diameter does NOT yield throw… any talk of “diameter” that does not include “focal length” ? is a LIE.

all the luminous intensity calculations in the world? the lens doesnt care what you think you calculated… the lens only knows…

diameter
focal length

and the ratio of those? the f-number? which is the numerical aperture? is all there “is” to judge the effectiveness of 2 lenses by… anyone who says “diameter = throw” does not have any numbers,indeed, any “real accepted definition” to back them up, and countermand anything i have stated here.

you can not like my attitude, and you can think of my confidence in these statements as “pride”, “rudeness”, “ego”, you can click “rude” all day long? its not going to change the laws of physics one iota.

we can “set” the f-number as low as we want it to be? simply by choosing 2 lenses, of different focal lengths, and using the “compound lens formula” to tell us how we are doing…

the front diameter? will still be the “diameter”… the new compound overall focal length? will still be the focal length of the new lens we made… and the f-number will still be the ratio of the two.

you can cast aspersions on my attitude, you can make fun of any mis-spelled words, or, the “style” i write with isnt to your personal grammatical liking.

when you bring something more concrete to the table? let me know… i will be waiting quite some time for that…

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this isnt my “pet theory”… this is “fact”

gloves on the ground… pick it up to defend the statement

“only diameter yields throw”.

its wrong. it needs to be put to rest? in a shallow unmarked grave…

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all… there… is

to “see” in the edmunds optics paper? to “model” a single lens zoomie? is all “NA”. numerical apertures… really nothing else.

numerical aperture, the illumination engineers entire way of modeling it? is… F NUMBER. they are the same thing.

the fact it gets stated as a trig function? is like speaking french instead of spanish… the word still means the same thing.

they state EXPLICITLY, that you are looking for a single lens, that has the numerical aperture with the “correct angle” that the LED source emits… that the lens will accept.

numerical aperture? is F-number… they are the SAME EXACT THING.

not once did the paper mention “throw”. not ONCE did it state “just get a bigger diameter lens to increase the throw”… no. What it says is, that you NEED the proper NUMERICAL APERTURE.

numerical aperture? is exactly the same thing as F NUMBER… they are the same thing.

all the engineers are saying? over and over again in the calculations of the equations? is this, translatred from french into english:

“you need to find a lens with a lower F NUMBER that will have the correct angle or better.”

when you shift from single lens to pre-collimated system? they explicitly state:

“you are creating a ratio of the 2 focal lengths, to create the NUMERICAL APERTURE you need.”

which is to say…

“you need to create the proper F number”.

if the “Coghlans law of absolute throw”, which states that “only bigger diameter gives more throw” was something real and concrete? Then why, pray tell me… did the engineers concern themselves only with “numerical aperture”? which is the exact same thing as “f-number” stated differently?

hm?

because “diameter = throw” without taking into consideration focal length? is made up crap that dosnt exist.

i cant find this “important concept” stated anywhere, except on flashlight sites… and i dont know WHERE it came from. NO CAMERA math websites say this… no telescope builders know about this “important fundamental concept”. The engineers at edmunds optics? THEY dont reference it.

because? it doesnt exist… its an internet fable. Its a MUCH loved and entertaining “urban myth” that no camera guy would ever entertain.

why is a flashlight site? the only place i can find this oh-so-important “law”? someone, somewhere along the line? mis-understood something someone stated, and it got repeated so much, everyone believes it…its a myth.

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and stay on point…

i say, that the statement “only diameter yields throw” is poppycock?

you show me ONE credible source? that backs this statement up. nowhere does it exist… it only exists in the mind of flashlight site posters.

if i say this on a CAMERA site? they will laugh at me, and politely explain “what an f-number is” and how to use it… if i say it on a telescope building site? they will laugh at me, and politely explain how i dont kow what is actually going on, and will explain their way they use the “F” concept… and obviously the optics engineers at EDMUNDS OPTICS, wrote an entire math paper? they will explain what a “numerical aperture” is…

and ALL of this? is simply the ration of diameter to focal length.

no equation, ANYWHERE… ever once, states that “diameter alone” makes more light going thru the lens.

go on, show me ONE SOURCE for the statement. anywhere? except some unsupported statement on a flashlight site… and the statement? is completely undefendable.

what obviously happened years ago? was someone once said “if you increase the diameter of your lens, and KEEP THE SAME FOCAL LENGTH… only then will you send more light downrange…”

and in typical human being fashion? they remembered HALF the statement, forgot the other half, did NOT understand f-number or numerical aperture? and it got repeated over and over again until you all believe? a completely useless concept, that is completely a lie.

you cant show me ONE… SINGLE… SOURCE… anywhere.

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Who are you talking to?
Who is the guy that said only diameter matters? I’m pretty sure whoever said that was in the other thread you were replying to.
Use the quote button if you’re talking about someone specific.
It’s at the bottom right.

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when your ray traces demonstrate the simple optics math and rules that exist everywhere else except on flashlight sites? i’ll begin to take them more seriously…

why dont you take your “ray traces” that claim the “established math” of compound lenses is wrong? and CHANGE wikipedia optics page?? and see how quick the rest of the OPTICS world changes it BACK, and you get laughed at?

when your ray traces, square up with the rest of the optics world BASIC PRINCIPLES? we can talk. So far? they are about as useful as posting “warner brothers cartoons” in support of your math argument…

i’m standing on FIRM mathematical and optical ground…

show me, ONE SOURCE that says “only diameter passes more light thru a lens”.
show me ONE SOURCE that says 2 lenses touching doesnt keep the same diameter, and cut the focal length in half?

and i will agree to &^%$ your $#@! on main street? and give your four hours to DRAW A CROWD and sell tickets to the event.

=

i tried over and over again? to state the well established mathematical laws? everyone and their uncle keeps interrupting me and correcting me, as if i am a small child that does not grasp the “basic concepts” in the class room…

the only “citation” all you guys have for the statement “diameter equals throw”? is each other saying it. you are mathematically pooping your pants, and i am calling you on it. ALL of you.

all any of you can do? to support it? is say “well, i really really really believe it”… which is nothing.

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i have already USED the “compound lens formulas” in imaging? countless times? and they work JUST FINE, the way they are stated and intended to work. (its only your cartoons you keep posting for proof? that are mathematically suspect)

imaging FROM a light source, TO a lens? is mathematically NO DIFFERENT than doing the opposite, IE, focusing a light source thru a lens, onto a target… its the same thing.

i’m done with politeness? because everyone keeps trying to tell me i am wrong? and the whole rest of the optics and math world agrees with me.

=

what was your crack couple days ago, somethng “degrees”… “potatoes”… and only “useful work” counting for something?

show me ONE EQUATION, whereby “only diameter yields throw”… just ONE.

come on… it aint happening… it does not exist.

this myth is getting put to rest…

13

F NUMBERS MATTER

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:student:

15

What the heck are you talking about?
I agreed with you that the two lenses together had half the focal length just like you said…
I also never claimed that only diameter matters, that was someone else.
Maybe you should stop being so condescending and actually read what other people post?

16

then i apologize and i mean it… then its directed at the other 90 percent that keep telling me made up laws that dont exist… my “believing” this made-up and fundamentally incorrect law? thet keeps getting passed around?

got me made fun of on a camera site… it made the telescope builders question my sanity… it simply does not exist…

take my apology to heart then.

but nothing changes my challenge, for anyone to support the non-existent law “diameter = throw”.

it simply does not exist… and this is a “site wide” misconception…

people keep comparing lenses, and every time i say “look at the one with the lowest f-number? everyone keeps chiming in, with poop advice… and its all based on lies.

i wasted a good year or two of my LIFE operating on this “fundamental comcept”? and wondered why i had such trouble understanding mor equations and optics laws to further my own work…

this law of “only diameter yields throw”? needs replaced… with…

“only the f-number matters, only a lower f-number yields throw”

okay, it wasnt you… accept my apologies, and we’ll get back to the more important business, when this is done…

17

:+1:

18

sedstar: first I will say again that throw (defined as the luminous intensity of the beam, measured in candela) and light collection efficiency are two different things. I think you are are focusing on optimizing the light collection efficiency, which, while important, is not the same thing as throw. A light can have a lot of throw but have poor efficiency. For example a light with a large diameter lens and low NA.

Now, regarding whether the throw is proportional to the lens area. I will admit I can’t find any paper describing how to predict the throw of a flashlight. So I can only, again, refer to this thread. That Edmunds optics document seems to focus on light collection efficiency and does not talk about throw. But, again, throw and efficiency are different things.

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what i AM saying is?

luminous intensity has no PLACE in the lens selection and construction of a single lens zoomie. none. isnt even a consideration…

what emitter or other light source you select? thats up to you. whether you use a waiven collar or not? again, thats up to you. the ONLY thing that matters? is that the f-number of the lens? “matches” or exceeds the “f-number” of the source…

since the source isnt a lens, that statement appears non-sensical? but when you replace the word “f-number of the LED” with the phrase “numerical aperture” of both the lens and the source? it makes more sense.

stated yet another way? the angle of emission, whatever it may be? must be matched with a single lens of at least that angle, and more if possible.

this critical ANGLE, that the led source is coming out at? you get that easily, from the datasheet… the critical angle of the LENS? isnt that obvious… the only easy way to see that angle? is to make a rough drawing to scale, of the diameter of the lens, and the focal length back to the point the 3 lines intersect? and either be careful in your drawing to SEE that critical acceptance angle of the lens, or, to calculate it, using the dimensions of the lens (FL, diameter) to arrive at the F=number that presents that critical angle. (chief soh-cah-toa)

each and every time i mention the F-number? someone “corrects me” and states that “no no, that lens there, the one with bigger diameter? only diameter yields throw”, and its 100 percent completely false.

i am stating, that if you know the angle of emission of your source? then you use whatever method of calculating the angle of the lens?? only then can you match them, or, god forbid exceed that critical angle. (lord forbid you collect more than the half angle, and collect 3/4ths of it, lol)

this isnt an “important consideration” amongst other considerations? its the only consideration. its basically ALL the edmunds optics paper concerns itself with.

you figure out the “f-number” of a lens, that matches or exceeds this critical angle? you are home free… if you cant find or exceed this critical angle?? you still have a chance at it, by selecting 2 large diameter lenses, and using the compound lens formula to yield you new resultant focal length… this new “lens”? will yield you a lower better f-number… to try to match or exceed that critical angle with.

matching this critical angle? is not important… its all there is. you IGNORE any thought of “diameter equals throw” because its a patent lie.

===

then? armed with this f-number? that you have to meet or beat? NOW you can select your focal length… which paints as large (floody) or as small (pencil thrower)… as you would enjoy.

i am stating, its not an important consideration? its the only condideration… nothing else exists.

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I guess we can agree to disagree on this point.