Light lost in aspheric lens flashlight

Flashlight Modding and DIY Parts
21

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.

22

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(adding telephoto doubler lens on main t20 lenses) 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: 37.5cm fresnel lens spotlight build

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.

23

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.

24

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.

25

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%.

26

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.

27

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.

28

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

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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)

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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.

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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 (es)
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.

29

Yes :slight_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 3x42 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.

30

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.

31

That is it :slight_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 :slight_smile:

32

Very good result with the new lens! Well done!

33

link does not open.

34

Looks like the anchor optics site no longer exists. Edmund optics has a lot of the same stuff for similar prices. The lens that worked best for me is a 15mm diameter, 15mm FL plano convex lens with AR coating.

35

Thank you.