Light lost in aspheric lens flashlight

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EasyB
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Light lost in aspheric lens flashlight

Hello everyone:
I have a UF-1504 host on the way from mtnelectronics, so I’ve been thinking about how to optimize the flashlight. My goal with this flashlight is of course to have a lot of throw (cd), but I’m concerned about the low light extraction efficiency due to the light not collected by the lens when it’s in focused “spot mode”.

So I am planning on using a small collector lens very close to the LED to collect a good portion of the light that would just be lost. My understanding is that while this can significantly increase the light collection efficiency, it will not result in significant changes to the beam cd. In ray optics language, this is because when the collector lens is placed very close to the LED (within the focal length), this produces a virtual image that is larger than the actual LED. The large lens then sees this virtual image and focuses it. The result is the beam with the collecting lens in place is larger, but close to the same cd. This works for me because it makes the beam wider and more usable. There is some talk about collector (pre collimator) lens in this thread: http://budgetlightforum.com/node/33455

The reason I made this thread was to more closely analyze the light collection efficiency. Aspheric lenses used in flashlights usually have a focal length approximately equal to the lens diameter. This means the cone of light collected from the LED has a 26.6 degree half angle. Now how can we estimate what portion of the total light from the LED lies in this cone? We can do this using the “typical spatial distribution” plot in the XP-L data sheet. This shows the luminous intensity (cd) as a function of angle. It is greatest at 0 degrees (right above the LED), and goes to zero at 90 degrees (down to the side, parallel with the LED die surface). From this plot, one can see that there is a lot of light at half angles greater than 26.6 degrees, so the lens is losing a lot of light, but this plot doesn’t tell the whole story. To get the total light as a function of angle, one must integrate the light cone (integrate around the axis perpendicular to the LED surface). Doing this effectively weights the higher angles more because there is more light in the cone at higher angles. This adds a factor sin(theta), and this factor multiplied times the spatial distribution plot gives the total light as a function of angle.

If we approximate the luminous intensity in the spatial distribution plot as linearly decreasing with angle, the graph in this link:
wolframalpha.com/input/?i=(-63.69x%2B100)sinx+integrated+from+0+to+1.57
shows the total light as a function of half angle (in radians, so 1.57rad is 90 degrees). The area under the curve is the total light in different sized cones. The cone from 0 degrees to 26.6 degrees (0.464rad) has roughly only 25% of the total light from the LED. So a typical aspheric lens setup loses 75% of the light. Now if we use a collector lens close to the LED that collects a much larger cone, say with half angle 75 degrees (1.31rad), 94% of the light is collected.

Conversely, one can calculate the light collected by a typical reflector, which might collect all the light with half angle greater than 30 degrees (0.52rad). The light collected by this reflector would be 72%, so 72% of the light would be directed to the hot spot, while the rest would come out as spill.

I just realized that the extra sin(theta) factor should be included which is why I made this thread. I think the analysis is correct. What do you guys think? Like I said, there is some talk of people successfully using collection lenses in the thread I linked above, but I could not find anyone estimating how much more light was collected.
I’m planning on doing some measurements before and after I modify my UF 1504 with a collector lens, so we’ll see how much more light it collects.

djozz
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Thanks for the nice analysis Smile

What is not taken in account yet, is light loss from reflections. To get close to the same cd as without it, the pre-collimator lens should have a good anti-reflection coating.

Looking forward to your measurements!

(I did some measurements on the light loss in a zoomie a while ago, link)

EasyB
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Thanks for pointing out your measurements; I had come across them before but forgot about them. I think this really emphasizes the need for pre collimator lenses in these flashlights.
I have a small lens with AR coating in mind. Probably the 9mm diameter lens with 9mm FL from here:
http://www.anchoroptics.com/catalog/product.cfm?id=368
Not super cheap at $19, but I think these lenses are quality.

djozz
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Go to a flee-market and buy an old super8-camera, video camera or other obsolete optical stuff for a dollar. If you open up the multi-lens objectives it is full of high quality coated lenses, there’s good chance that there’s one with the right diameter and focal length.

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interestingg!
subbed

Fritz t. Cat
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The analysis seems correct, except that I would expect the intensity to be closer to the cosine of the angle than linear.
One can increase the spot size with a shorter focal length lens. Up to a point that is shorter than single element lenses usually get, there is not much loss in throw, because you are still collecting light from angles where the LED puts a lot of light. Shorter than that usually requires some sort of Fresnel lens. Using two lenses in series will have a similar effect to using a stronger lens, so that should work, at least to some extent, if you do it right.
First order optics is simple enough to do by hand or you can write a simple program.
If you program and and know some mathematics, it isn’t too bad to write a ray tracing program to get a handle on how much light will get through. Doctor Jones has done that for reflector lights. Or you can just try it various ways.
This is a good all refracting flat Fresnel lens http://www.dhgate.com/product/flat-fresnel-lens-for-stage-light-with-siz.... It has size 130 mm. and focus 50 mm. It is so strong that the light at the edges looks distinctly yellow.
POP lites, LED Lensers and Coasts use two zone Fresnel lenses.

Flashlight designers should look at lighthouses and pottery.
这些谁设计的手电筒应该看灯塔,以及在陶器。

EasyB
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Fritz t. Cat wrote:
The analysis seems correct, except that I would expect the intensity to be closer to the cosine of the angle than linear. One can increase the spot size with a shorter focal length lens. Up to a point that is shorter than single element lenses usually get, there is not much loss in throw, because you are still collecting light from angles where the LED puts a lot of light. Shorter than that usually requires some sort of Fresnel lens. Using two lenses in series will have a similar effect to using a stronger lens, so that should work, at least to some extent, if you do it right. First order optics is simple enough to do by hand or you can write a simple program. If you program and and know some mathematics, it isn’t too bad to write a ray tracing program to get a handle on how much light will get through. Doctor Jones has done that for reflector lights. Or you can just try it various ways. This is a good all refracting flat Fresnel lens http://www.dhgate.com/product/flat-fresnel-lens-for-stage-light-with-siz.... It has size 130 mm. and focus 50 mm. It is so strong that the light at the edges looks distinctly yellow. POP lites, LED Lensers and Coasts use two zone Fresnel lenses.

You are right that the intensity vs angle is close to cos(theta), but wolfram alpha would not calculate the answer in that case because it took too much computation time, so I went with the quick approximate answer.

That is a strong Fresnel lens, maybe the strongest lens in general that I have seen for sale, but it would still only collect about 67% of the light from the LED, though it would make a nice light weight spotlight. I hope that a well designed two lens system can get higher light collection efficiency. I have been doing some calculations and it seems the pre collimator lens should be as strong as possible for this purpose. There is a 20mm diameter, 11mm FL lens at edmund optics.

By the way, check out this two lens thrower I put together a while back. It worked out pretty well, but I didn’t really take any measurements regarding the light extraction efficiency.
http://www.candlepowerforums.com/vb/showthread.php?282184-SST-50-homemade-spotlight

djozz
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That was 2 years before I joined CPF and later BLF Smile

That was a really cool light, optically well thought out. I wonder what the throw number was (is?).

EasyB
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djozz wrote:
That was 2 years before I joined CPF and later BLF Smile

That was a really cool light, optically well thought out. I wonder what the throw number was (is?).

Thanks. I still have it but it is disassembled. It never got past prototype state, so it was fragile and awkward to use. As it was in the thread I would guess it had 300-350kcd. It could be much higher now I think, if I installed a brighter, dedomed LED. One of my favorite things about flashlights is they can be so portable, so this UF 1504 that I’m building, to me, is sort of a new and improved version of that light I built 6 years ago.

Rufusbduck
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I thought it was interesting how Ervin used a small aspheric situated at its focal point within a large reflector to both capture and focus virtually all emitted light. It seemed pretty effective.

Three Tanna leaves to give him life, nine to give him movement. But what if he eats the whole bag?

Scott

EasyB
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Rufusbduck wrote:
I thought it was interesting how Ervin used a small aspheric situated at its focal point within a large reflector to both capture and focus virtually all emitted light. It seemed pretty effective.

http://budgetlightforum.com/node/30598

That is a neat idea and impressive execution.

Fritz t. Cat
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EasyB wrote:
the intensity vs angle is close to cos(theta), but wolfram alpha would not calculate the answer in that case because it took too much computation time, so I went with the quick approximate answer.

The inefficiency of software never ceases to amaze me. That should take something like a microsecond per angle on a laptop.

Flashlight designers should look at lighthouses and pottery.
这些谁设计的手电筒应该看灯塔,以及在陶器。

luminarium iaculator
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I like this type of threads,

Did you seen this thread: http://www.candlepowerforums.com/vb/showthread.php?365868-Dereelight-DBS-with-de-domed-XP-G2-and-pre-collimator-lens

EasyB
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luminarium iaculator wrote:
I like this type of threads,

Did you seen this thread: http://www.candlepowerforums.com/vb/showthread.php?365868-Dereelight-DBS-with-de-domed-XP-G2-and-pre-collimator-lens

That certainly looks like a good result. It seems like he is getting good light extraction efficiency from his ceiling bounce test comparison to the 860 lumen light.

There is no direct before/after comparison for adding the pre collimator lens, but we can tell something from the beam shots. I assume the XP-G was dedomed. The XP-G with pre collimator has about the same area in the beamshot as the dedomed XM-L which has about double the die area as the XP-G. So the light collection efficiency approximately doubled by adding the precollimator lens.

djozz
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I can’t help plugging my own fresnel lens contraption here that I made last year Innocent http://budgetlightforum.com/node/41062

luminarium iaculator
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EasyB wrote:
luminarium iaculator wrote:
I like this type of threads,

Did you seen this thread: http://www.candlepowerforums.com/vb/showthread.php?365868-Dereelight-DBS-with-de-domed-XP-G2-and-pre-collimator-lens

That certainly looks like a good result. It seems like he is getting good light extraction efficiency from his ceiling bounce test comparison to the 860 lumen light.

There is no direct before/after comparison for adding the pre collimator lens, but we can tell something from the beam shots. I assume the XP-G was dedomed. The XP-G with pre collimator has about the same area in the beamshot as the dedomed XM-L which has about double the die area as the XP-G. So the light collection efficiency approximately doubled by adding the precollimator lens.

Vinz is really advanced modder. I wonder what happened with him? He was member here on BLF?

That was 3 years ago. Pre collimator lenses(really working, confirmed and tested by various people) and tint changing of de domed emitters are his biggest inventions… Everyone talked about it at that time and just few people managed to crack right pre coolimator lenses and to change tint with “diamond treating” as he said :).

We can tell a lot from that picture… It is 100% bigger die projection without lux drop. That is huge upgrade to led because dedomed XP-G2 grows to XML dedomed size(xml grows even bigger Smile )

I tried one pre collimator lenses and I got MTG2 size projection of XP-G2 but about 50% lux drop with poor flood mode. So in aspheric flashlight if you achieve bigger die projection with pre collimator lenses you will have extreme hotspot size with poor flood mode.

I think a lot can be achieved with right lens choice and placement which is not easy at all. It needs to be placed around 0.7mm above led as Vinz said.

MACS0647
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So due to my lacks of knowledge in such deep details, I’ve nothing to add to the technical debate about pre collimator lenses,
but since a couple of times ago Vinz had pimped up some of my Dereelight pills for the Night Masters and X-Searcher,
I can show you a practicle kind of example.

!!
!!

The effect of the pre collimater:

!!


!!
Allthoug the X-Searcher and the UF. 1504 have nearly the same headsize (maybe the X-Searcher is a little bit smaller), I think it’s good to see that the spot of the X-Searcher is quite significant larger.

As I remember it well, Vinz said that by using such a pre lens you might have a very little loss of lux (around ca. 5 %),
but this price is worth to pay for, concerning to the amount of lumens you are gaining, which in relation should make the pre collimator
even more effective with a brighter LED.

Some Beamshots of the Night Master and the X-Searcher (and other companions) with a pre collimator XP-G2 ded. / XM-L2 ded.
you can also find here – http://budgetlightforum.com/node/45563

luminarium iaculator
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We needed such reply in this thread Smile

About this “Vinz said that by using such a pre lens you ‘ve a very little loss of lux (around ca. 5 %)”

He said once that even small lux gain can be achieved sometimes. But mostly it is 0 or +- 5% which depends on how accurate you placed lenses.

EasyB
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Thanks for these pics, MAC. I think that is close to the before/after comparison I was looking for.

luminarium iaculator wrote:
EasyB wrote:
luminarium iaculator wrote:
I like this type of threads,

Did you seen this thread: http://www.candlepowerforums.com/vb/showthread.php?365868-Dereelight-DBS-with-de-domed-XP-G2-and-pre-collimator-lens

That certainly looks like a good result. It seems like he is getting good light extraction efficiency from his ceiling bounce test comparison to the 860 lumen light.

There is no direct before/after comparison for adding the pre collimator lens, but we can tell something from the beam shots. I assume the XP-G was dedomed. The XP-G with pre collimator has about the same area in the beamshot as the dedomed XM-L which has about double the die area as the XP-G. So the light collection efficiency approximately doubled by adding the precollimator lens.

Vinz is really advanced modder. I wonder what happened with him? He was member here on BLF?

That was 3 years ago. Pre collimator lenses(really working, confirmed and tested by various people) and tint changing of de domed emitters are his biggest inventions… Everyone talked about it at that time and just few people managed to crack right pre coolimator lenses and to change tint with “diamond treating” as he said :).

We can tell a lot from that picture… It is 100% bigger die projection without lux drop. That is huge upgrade to led because dedomed XP-G2 grows to XML dedomed size(xml grows even bigger Smile )

I tried one pre collimator lenses and I got MTG2 size projection of XP-G2 but about 50% lux drop with poor flood mode. So in aspheric flashlight if you achieve bigger die projection with pre collimator lenses you will have extreme hotspot size with poor flood mode.

I think a lot can be achieved with right lens choice and placement which is not easy at all. It needs to be placed around 0.7mm above led as Vinz said.

I’m aware of the principles and compromises of using pre collimator lenses. I made a larger version of the two lens system back in 2010 (CPF thread linked above).

The objective is to collect most of the light with the pre collimator lens and have the lens project the light in a smaller cone towards the main lens. The picture below is of the light that I made, with the lenses in the optimal positions, with the cone just filling the main lens.

If the pre collimator lens were closer to the LED, the light cone would become larger and it would overfill the main lens, losing some light around the edges. If it were farther away, the cone from the pre collimator to the main lens would be more narrow, but then the pre collimator lens would not collect as much light from the LED.

The pre collimator lens should have as large a diameter:focal length ratio as possible to optimize light collection (a ratio of around 2 is what I used in the above picture). If you are familiar with ray optics or play with a calculator like this one:
http://www.photonics.byu.edu/Thin_Lens_Calc.phtml
you can see that when the LED is very close to the lens the image is close to unchanged in position and magnification. When the LED is close to the focal length, but inside the focal length, the image appears to be farther away from the lens and there is significant magnification. The light cone from the pre collimator lens is very narrow in this configuration. The magnification is what causes the beam to enlarge; the image that the main lens sees is larger than the actual LED. Some position in between these two extremes will be the optimal position for the two lens setup. The reason you want as large a diameter:focal length ratio as possible is so the pre collimator lens is as close as possible to the LED when the light cone just fills the main lens.

In the picture above, the light coming from the pre collimator lens appears to be coming from an image of the LED that is slightly below the actual LED and slightly larger.

sedstar
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there are two ways to use two lenses…

1) you arrange them in a typical Galilean Telescope fashion.

or…

2) you are actually making a “compound lens”. the rear lens closest to the light source is typically the shorter FL. The bigger FL lens is out front. FL of the NEW resultant compound lens? is determined by FL-1 and FL-2, and the airgap between them.

some general rules…

a) two lenses of equal FL, touching (airgap = 0mm) will make a single compound lens of exactly half. Example, two 100mm FL lenses touching? make a new compound lens of 50mm FL.

b) using example a… as you introduce airgap bigger than 0mm (not touching), the FL of the compound lens gets closer to 100mm FL, but never quite reaches it.

c) as the airgap gets bigger? the rear lens gets closer to the light source

d) the SIZE of the well focused emitter? is determined solely by the FL of the resulting compound lens. Smaller overall FL, bigger die projection size. larger overall FL, smaller die projection.

e) cigarette smoke is your friend for seeing you are not wasting light from lens to lens, lol.

f) theres no reason to limit yourself to 2 lenses, grasshopper… i have used 3 and 4 lenses before, with IR LED’s… to good effect.

g) since 2 lenses actually form ONE compound lens? and another 2 lenses form a second compound lens? using those 4 lenses, is actually like using 2 lenses, for the purposes of the math governing it.

h) if the two lenses are different FL? radically different? like… 25mmFL and 600mm FL ? the resulting lens will be a lot closer to 25 than to 600… but theres equations you can work out to accurately predict it based on both FL’s, and the airgap.

============================================================

everytime i brought this idea up HERE, and on my other site? everyone poo-pooh’s the idea, and makes up ideas why it doesnt work and how it cant be efficient… even though the MATH shows it works. (also? Dr Jones described it… also? a “white paper” from edmunds describes it…)

I only use it on IR emitters… i’m glad someone started doing it with visible light…

With enough black coffee and cigarettes? all things are possible…

I am currently still shipping… REAL GENUINE CREE xp-g emitters, the classic… brace yourself? as low as 20 cents apiece!! Check out the SALES THREAD, everyone is happy… then PM me

SALES THREAD:
http://budgetlightforum.com/node/52528

if you are into reloading? this is my site… I inherited the remains of what was once arguably the best reloading site on the internet… its the “BLF” of reloading sites…

http://reloadbench.freeforums.net/

if you think night vision would be cool? It IS… this site i am a member of, and its basically the “BLF” of home made scratch-built digital night vision. They are at the leading forefront of advanced DIY for digital night vision, and thats gun mounted or handheld… builds rival and exceed commercial offerings…

http://nightvisionforumuk.com/

sedstar
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when you use 2 lenses, and 2 lenses… and put THOSE two compound lenses together and use them as if they were 2 lenses? you have the advantage of tuning the system greatly…

1) you can adjust the FL of compound lens 1, by adjusting the airgap.
2) you can adjust the FL of compound lens 2, by adjusting THAT airgap.
3) you can adjust the FL of the overall 4 lens system? by adjusting the airgap between both compound lenses…

its a lot easier tuning a 4 lens setup with visible light and cigarette smoke, LMAO, i was working with infrared emitters… it was a PITA… ha ha.

With enough black coffee and cigarettes? all things are possible…

I am currently still shipping… REAL GENUINE CREE xp-g emitters, the classic… brace yourself? as low as 20 cents apiece!! Check out the SALES THREAD, everyone is happy… then PM me

SALES THREAD:
http://budgetlightforum.com/node/52528

if you are into reloading? this is my site… I inherited the remains of what was once arguably the best reloading site on the internet… its the “BLF” of reloading sites…

http://reloadbench.freeforums.net/

if you think night vision would be cool? It IS… this site i am a member of, and its basically the “BLF” of home made scratch-built digital night vision. They are at the leading forefront of advanced DIY for digital night vision, and thats gun mounted or handheld… builds rival and exceed commercial offerings…

http://nightvisionforumuk.com/

luminarium iaculator
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You guys are talking about and you all made double lens systems lights.

There are diy lights with triple or more lens system and I’ve also done them. Seedstar will be familiar with them (T20 with doubler and Sunnranger). T20D SR(adding night vision IR coated objective lens instead of stock T20 lenses). All of them have recessed flood comparing to stock light.

While they have very clear die projection and indeed performance will improve over stock T20 neither of them can’t beat quality single aspheric setup (50mm).

This are nice experiments indeed:
EasyB: http://www.candlepowerforums.com/vb/showthread.php?282184-SST-50-homemade-spotlight
Djozz: http://budgetlightforum.com/node/41062

Double or multiple lens system is different story for me and although small lenses in front of emitter of mentioned setups are pre collimator I don’t experience them like that.

I experience pre collimator as emitter dome replacement which protects emitter and enlarges main beam projection… Possibly without loosing lux performance or small gain if possible, and I really think it must be in as small configuration as possible.

EasyB
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I got my UF-1504 and installed an XP-L HI V2 1A emitter and FET driver from mtnelectronics. First, I made some external modifications. The big square protrusions on the body and tailcap make it uncomfortable to hold, so I removed them. I don’t have access to a lathe, so I used a saw, dremel, and file. It looks a bit rough, but it is now much nicer to hold in the hand, and I can now comfortably use an overhand grip, which was very uncomfortable in stock form. I also attached a belt clip to the head.

I then went about searching for a suitable lens to use as a pre collimator lens. I decided that the included threaded retaining ring would make a great height-adjustable lens mount. I decided on a 15.3mm diameter double convex lens with 7.6mm FL from anchor optics. It does not have AR coating. I wanted as strong a lens as possible and there was not an AR coated lens available that was as strong.

I drilled out the retaining ring to 12.5mm, then used a dremel and file to enlarge the ID to ~15.5mm. The lens just fits inside. I put small dots of epoxy around the perimeter to secure the lens to the retaining ring.

Here it is installed in the pill.

I adjusted the height of the pre collimator lens so that the cone of light just filled the main lens, as I described a couple posts back.

With a purple Efest 4200mAh 26650 cell at ~4.16V OC, I measured 5.3A bypassing the tailcap. I measured my ammeter resistance to be ~35mOhms. I took before and after pictures and lux measurements. The exposure settings were not controlled, so the pictures should only be used to compare the beam sizes. I recently bought a Tondaj LX-1010B which I used for the lux measurements here. Note that this meter reads high for cool white tints like the 1A. From djozz’s excellent measurements here


Stock light without pre collimator lens.
11,800 lux at 6.05m: 432,000 cd
approximate beam size: 20cm x 20cm
very approximate lumen estimate= 0.2m x 0.2m x 11,800lux = 472 lumens


With precollimator lens adjusted so cone just fills main lens.
8,600 lux at 6.05m: 315,000 cd
approximate beam size: 33.5cm x 33.5cm
very approximate lumen estimate= 0.335m x 0.335m x 8,600lux = 965 lumens


For this shot I adjusted the precollimator lens slightly closer to the LED, so that the light cone just overfills the main lens. I will lose a bit of light, but will pick up some cd.
9,800 lux at 6.05m: 359,000 cd
approximate beam size: 30.5cm x 30.5cm
very approximate lumen estimate= 0.305m x 0.305m x 9,800lux = 911 lumens

I’m pretty happy with the result; about double the beam lumens with not too bad an intensity drop. It could be improved by using a suitably strong precollimator lens with AR coating. I also bought a 15mm diameter plano-convex lens with 15mm FL and AR coating. I may try this lens in the future to see how it works in the light.

luminarium iaculator
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You did fine job there.

You got main beam enlargement but I think to many cd loss (about 30%)…

Search another lens combination. I don’t think they should be AR coated either.

djozz
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Nice measurments! The results are quite as expected, but without experiments you will never know, sometimes things are quite different than theory.

A thought that is not neccessarily correct: What is decreasing your luxvalues when using a collimating lens (apart from reflection/absorption losses) is that the beam intensity is not constant at all angles, but decreases with angle. So pre-collimating will project more of the lower-intensity edge of the beam on the lens, effectively decreasing the lens diameter and thus spot brightness. You showed that nicely in your last experiment with the pre-collimating lens a bit closer to the led.

About the Tondaj meter, I just re-read my luxmeters-post and realised: it over-reads cool white leds, but the 16% over-reading with a cool white XM-L (in a cheap dive-light) that I found in the test, later appeared to be a fake Latticebright led with a huge blue component in the spectrum (see Hannes’ post from yesterday), real XM-L’s have never been so blue so the over-reading of a genuine Cree will not get as high as 16%.

EasyB
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djozz wrote:
Nice measurments! The results are quite as expected, but without experiments you will never know, sometimes things are quite different than theory.

A thought that is not neccessarily correct: What is decreasing your luxvalues when using a collimating lens (apart from reflection/absorption losses) is that the beam intensity is not constant at all angles, but decreases with angle. So pre-collimating will project more of the lower-intensity edge of the beam on the lens, effectively decreasing the lens diameter and thus spot brightness. You showed that nicely in your last experiment with the pre-collimating lens a bit closer to the led.

About the Tondaj meter, I just re-read my luxmeters-post and realised: it over-reads cool white leds, but the 16% over-reading with a cool white XM-L (in a cheap dive-light) that I found in the test, later appeared to be a fake Latticebright led with a huge blue component in the spectrum (see Hannes’ post from yesterday), real XM-L’s have never been so blue so the over-reading of a genuine Cree will not get as high as 16%.

That’s an interesting thought/interpretation which I’m sure there is some truth to.

Ah, okay. So without that data point it looks like the Tondaj meter reads about 5% high for cree cool white LEDs.

EasyB
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luminarium iaculator wrote:
You did fine job there.

You got main beam enlargement but I think to many cd loss (about 30%)…

Search another lens combination. I don’t think they should be AR coated either.

The lux loss was more than I hoped. However, apart from the lens not being AR coated, I think its specifications are almost ideal for this use. There is room for improvement to the beam cd by adjusting the position of the pre collimator lens even closer to the LED. Moving the lens closer to the LED will throw away more of the light, but it will be the lower intensity light at lower angles. So it seems the precollimator lens position is a compromise between total lumens collected and resulting beam intensity. I will do some more testing to see what position I like best.

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if you analyze the VARIABLES here? I come up with, off the top of my head:

1) Focal length of primary lens
2) Focal length of pre-collimator lens
3) airgap between #1 and #2 lens

since both lenses “combine” to yield one COMPOUND lens? adjusting the back focal length (distance of pre-collimation lens to LED gap) is really just adjusting the airgap (#3)

I suppose i could add…

4) diameter of primary lens
5) diameter of precollimator lens

===================================================

when i did this? i was primarily concerned with an infrared illuminator. I tried working with visible light, since i was able to blow smoke into the lenses/light area, and adjust for less “lost” light… but, this didnt translate into “best” when switched over to infrared, since infrared refracts differently than visible thru each lens.

i instead settled on “tuning” everything tediously by hand. I was watching a monitor, and adjusted for best “distance” achieved. (the further away i got a “shootable” image, the better the result)

===================================================

now, you can tell me ALL DAY (and people did, lol) how this system of multiple lenses was inefficient, and doesnt really work? and how my eyes working with best image on a monitor can be fooled… shrugs

all i KNOW is, real life results mattered when trying to get more distance out of night vision.

I ALSO heard a lot of “welllll. if it REALLY works? You should be able to prove it… by putting a known emitter of known bin… with a known driver… and demonstrating this superior system”

which would be NICE, but… i already knew that tuning to visible light, then switching to IR ? wasnt best results… it was logical that tuning to IR, then switching BACK to visible wasnt going to be any different.

===============================

meters and spheres and calculated lux/candela/whatever figured are NICE, but… seeing the well focused emitter FARTHER is what really matters in the end. whether its a “wow!” moment with the naked eye and visible light, or, seeing a shootably bright image on a screen for night vision in the infrared region.

reading all this now? i think getting the brightest close by FLOOD, and getting the brightest focused emitter at DISTANCE, might be at odds with one another.

====================================

by the way, my system was “different” in a couple key ways…

1) i worked with IR, not visible light
2) i moved the EMITTER to focus or defocus, not moved the LENS
3) i used 3 and 4 lenses in my systems i made
4) i worked off of a p60 as a base, and had the first lens right at the end of the p60 reflector, which moved with the p60 module, obviously… the other 2/3 lenses stayed in place.

With enough black coffee and cigarettes? all things are possible…

I am currently still shipping… REAL GENUINE CREE xp-g emitters, the classic… brace yourself? as low as 20 cents apiece!! Check out the SALES THREAD, everyone is happy… then PM me

SALES THREAD:
http://budgetlightforum.com/node/52528

if you are into reloading? this is my site… I inherited the remains of what was once arguably the best reloading site on the internet… its the “BLF” of reloading sites…

http://reloadbench.freeforums.net/

if you think night vision would be cool? It IS… this site i am a member of, and its basically the “BLF” of home made scratch-built digital night vision. They are at the leading forefront of advanced DIY for digital night vision, and thats gun mounted or handheld… builds rival and exceed commercial offerings…

http://nightvisionforumuk.com/

luminarium iaculator
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EasyB wrote:
So it seems the precollimator lens position is a compromise between total lumens collected and resulting beam intensity.

Yes Smile

But real bingo with right precoolimator lenses is main beam enlargement without any lux loss…

So if you can make de domed xp-l size projection out of high intesity XP-G2 without lux drop that is real achievement…

In other words it does not have to be 200-300% larger… It is enough to be just 100% larger but without lux drop.

Precoolimators have one downside. Loosing generous flood mode. You loose less with smaller beam projection. The bigger precoolimator die projection creates smaller flood mode from mine experience.

I can bet you loosed a lot of usable flood mode with this precoolimator lenses. Right?

Seeds,
Lux meter never lies(of course they are not all calibrated well but will tell you what is happening between same testing configurations).
If you build multiple lens system with visible light and lux meter does not show as good results as with single aspheric setup that same will happen with IR invisible light.

Neither T20 with doubler neither t20 with yukon 3×42 lenses(sunnranger it is overrated myth with guys who does not know modding stuff) can’t out throw single quality 50mm flashlight setup, and not only that… They will have terrible flood mode comparing to single lens setup…

I don’t consider precoolimator as double lens system(although it is) I perceive it like emitter protection and a way to enlarge main beam in aspheric lights without lux loss and with lumen gain.

From this thread everyone can see what is happening with right lens selection. Very good thread.

EasyB
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I could not get the beam intensity above about 360kcd with the 15.3mm x 7.6mm FL lens, so I guess it was not as ideal for this purpose as I thought. When I tried moving the pre collimator lens even closer to the LED in order to reduce the LED image size and increase beam intensity, I could not get the image to focus as well. I had ordered an additional pill and retaining ring from gearbest which just arrived today. I modified this retaining ring so I could use the other lens I bought, a 15mm x 15mm FL plano convex lens with AR coating.

With the light cone overfilling the main lens roughly 1cm on each side, I got a good result.

11,340 lux at 6.05m: 415,000cd
approximate beam size: 29cm x 29cm
very approximate beam lumen estimate: 0.29m x 0.29m x 11340lux= 953lumens

This is about 2.1x the beam area of the stock configuration without precollimator lens with very close to equal beam intensity.

luminarium iaculator
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That is it Smile

200% bigger die projection without lux drop… That is achievement! Imagine old XP-G2-S4-2B inside (It will go over 500 kcd)…

Now even flood mode will be more intense but not so wide…

One beam-shot when you’ll have time please Smile

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