lucca brassi
Enlightened
I like to ask you which formula use for calculation of led thrower torches with pre collimating lens and primary aspheric lense (frensell ). (led - aspheric lense - aspheric lense)
thanks
thanks
equation (led- aspheric lense - aspheric lense)
- Thread starter lucca brassi
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Walterk
Enlightened
There are a lot of formulas - but what is it you wanted to use as givens/end result?
The appropriate formula will require that you have at least some starting point...and a desired end point/objective.
IE: If you know the beam angle, you can then find the beam width at any given distance.
If you know the lux at any given distance or the cd of the light, you can then find the lux on targets at any given distance.
What is it you know, and what is it you are trying to calculate?
bshanahan14rulz
Flashlight Enthusiast
I've had a similar question: what qualities to look for in a "precollimator" lens that you place close to the LED. Is it a short focal length lens with the FL at the emitter? Is it a long FL lens with emitter way inside of FL?
Let's say you have an aspheric with FL of 10cm, but diameter isn't enough to cover entire output of raw LED. So, you use a precollimator close to the LED that can gather more light than the aspheric would @ 10cm away. But what parameters of the precollimator affect where to place the final aspheric?
Is this stuff just easier to get a feel for by obtaining assorted optics and just tinkering? I guess we were probably hopign there was a nifty ray trace applet for systems with 2 or more lenses.
Let's say you have an aspheric with FL of 10cm, but diameter isn't enough to cover entire output of raw LED. So, you use a precollimator close to the LED that can gather more light than the aspheric would @ 10cm away. But what parameters of the precollimator affect where to place the final aspheric?
Is this stuff just easier to get a feel for by obtaining assorted optics and just tinkering? I guess we were probably hopign there was a nifty ray trace applet for systems with 2 or more lenses.
lucca brassi
Enlightened
Hi all !
Thaks WalterK , have allready read , very usefull !
Problem is simple .... all my led diving lights are based on SST-90 emiter ( high lumen output , high surface brightness , very robust led also could use for video if change inner focus on
screw ) , in housing which is limited with 50,5mm in diameter ( in length I have little reserve ) I also use DX aspherics lens with 44 mm (40mm without edge ) and focus at 18mm. Led is
driven at 10A.
Light is powerful and bright tight beam (cca 7° ) , but somewhere beyond 5 m, the beam suddenly extended ( like some funnel ) , which I think is problem of bigger die and small aspherics
lens.
I know mantra ( smaller die , bigger lens diameter , deeper reflector ,....) . But I like to correct that on existing system as much as it is possible.
I don't have picture at the moment but it is similar to that video http://www.vielviellicht.de/ just that led expands very fast cca 30 cm.
Mine do that some 1,5m away ( still have at 1m square 16x16cm and at 5m square 63x63cm , but it highlight a house next to me in distance cca 10m at least 4 m x 4 m .
I don't need some long throw , but I need powerfull beam on short distance ( 30m ) to penetrate murky water and beam must be '' slim formed ''
-----------------------------------------------------------------------------------
I'm looking on several sides like :
http://www.wavien.com/shop/rlt-collars/rlt-collar/ which I think would form tighter exit beam ( from 120° to 28° (small with 12.5mm aperture , because 32mm is outer
diameter and I have 50mm frensell lens with I think 35mm focus ) ....... personal I have mixed feelings :-(
I also don't like dedooming special SST-90 have many bonds , and I dont like to burn out phosphorus :-(
Thaks WalterK , have allready read , very usefull !
Problem is simple .... all my led diving lights are based on SST-90 emiter ( high lumen output , high surface brightness , very robust led also could use for video if change inner focus on
screw ) , in housing which is limited with 50,5mm in diameter ( in length I have little reserve ) I also use DX aspherics lens with 44 mm (40mm without edge ) and focus at 18mm. Led is
driven at 10A.
Light is powerful and bright tight beam (cca 7° ) , but somewhere beyond 5 m, the beam suddenly extended ( like some funnel ) , which I think is problem of bigger die and small aspherics
lens.
I know mantra ( smaller die , bigger lens diameter , deeper reflector ,....) . But I like to correct that on existing system as much as it is possible.
I don't have picture at the moment but it is similar to that video http://www.vielviellicht.de/ just that led expands very fast cca 30 cm.
Mine do that some 1,5m away ( still have at 1m square 16x16cm and at 5m square 63x63cm , but it highlight a house next to me in distance cca 10m at least 4 m x 4 m .
I don't need some long throw , but I need powerfull beam on short distance ( 30m ) to penetrate murky water and beam must be '' slim formed ''
-----------------------------------------------------------------------------------
I'm looking on several sides like :
http://www.wavien.com/shop/rlt-collars/rlt-collar/ which I think would form tighter exit beam ( from 120° to 28° (small with 12.5mm aperture , because 32mm is outer
diameter and I have 50mm frensell lens with I think 35mm focus ) ....... personal I have mixed feelings :-(
I also don't like dedooming special SST-90 have many bonds , and I dont like to burn out phosphorus :-(
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Walterk
Enlightened
So your beam has a waist at 1,5m, and at 5 meter the beams goes suddenly wider ?
bshanahan14rulz
Flashlight Enthusiast
^This is very common. Folks usually say, "That's just how it works, don't worry 'bout it." Is this true, or is this a symptom that the LED is not at the focal point of the reflector? It's not so much that from the aperture to the waist the diameter is decreasing, more that the divergence from diameter to the waist is one value, and then from the waist outwards it appears to diverge faster.
Mash.m, thanks for that tip, it looks great! Hope to have time tonight to play with it on my home PC.
Mash.m, thanks for that tip, it looks great! Hope to have time tonight to play with it on my home PC.
lucca brassi
Enlightened
foggy nights coming - I would take picture from side
BTW I have look your thread http://www.candlepowerforums.com/vb...ST90-focusable-handheld-searchlight&p=3557288 - nice work
is that ZENIT handle & teleobjective ?
it have lens not reflector
beam at 1m
beam at 5m
I have thought : I could defocuss it - specific for water , but I have to do that in pool
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Walterk
Enlightened
Sorry I don't see the problem 
. And if I did, I would not know what to do about it....
Probably has something to do with Lambertian lightdistribution over distance.
Try other lens, or try reflector instead of aspheric?
(Yes, thats a Zenith sniper, the DX73mm fits inside it. )
. And if I did, I would not know what to do about it....Probably has something to do with Lambertian lightdistribution over distance.
Try other lens, or try reflector instead of aspheric?
(Yes, thats a Zenith sniper, the DX73mm fits inside it. )
bshanahan14rulz
Flashlight Enthusiast
I think he's trying to convey that the beam diameter does something like this:
=<|=======<
Well, that turned out looking more like a fish. Basically, beam looks even and parallel until like, 3 or 4 meters out, and then it starts diverging.
After seeing some beamshots from some of the pros here, though, I am start to think reflector is not down far enough on LED (same with lens, lens not close enough to LED?)
=<|=======<
Well, that turned out looking more like a fish. Basically, beam looks even and parallel until like, 3 or 4 meters out, and then it starts diverging.
After seeing some beamshots from some of the pros here, though, I am start to think reflector is not down far enough on LED (same with lens, lens not close enough to LED?)
Beams typically are going for convergence several meters away, not divergence.
If divergence is happening, my first guess would be that the light was being sent ACROSS the focal point, essentially a pigeon-toed aim rather than a collimated beam.
That would create a bright center close up, but, the beam component's would not converge and continue outward, but CONTINUE TO PASS EACH OTHER through the center of the beam, and then continue on their merry way in opposite directions.
Does this sound plausible given the actual observations?
If you take a panel, and hold it front of the beam...you should be able to move it progressively further from the lens, and see the beam SIZE on the panel, and, you should see the size of the spot on the panel change and start to widen again disproportionally at a cross over point.
IE: Beams all get a bit wider as they get further from the light source, roughly (What I use at any rate for a rule of thumb):
(Beam Angleº)(0.018)(Range) = beam width at that range.
If you know what the beam angle should be, you can plug that in....if not, calculate it empirically from the spot sizes, etc.
At any rate, in far field, it should follow that relationship.
If you see an aberration, at a particular range...you can then try to make that range increase gradually, changing your focus, until the beam angle gets consistent again. (I'm assuming you'd be gradually increasing the distance at least...but depending on the set-up, I suppose it could be reversed, etc...)
If divergence is happening, my first guess would be that the light was being sent ACROSS the focal point, essentially a pigeon-toed aim rather than a collimated beam.
That would create a bright center close up, but, the beam component's would not converge and continue outward, but CONTINUE TO PASS EACH OTHER through the center of the beam, and then continue on their merry way in opposite directions.
Does this sound plausible given the actual observations?
If you take a panel, and hold it front of the beam...you should be able to move it progressively further from the lens, and see the beam SIZE on the panel, and, you should see the size of the spot on the panel change and start to widen again disproportionally at a cross over point.
IE: Beams all get a bit wider as they get further from the light source, roughly (What I use at any rate for a rule of thumb):
(Beam Angleº)(0.018)(Range) = beam width at that range.
If you know what the beam angle should be, you can plug that in....if not, calculate it empirically from the spot sizes, etc.
At any rate, in far field, it should follow that relationship.
If you see an aberration, at a particular range...you can then try to make that range increase gradually, changing your focus, until the beam angle gets consistent again. (I'm assuming you'd be gradually increasing the distance at least...but depending on the set-up, I suppose it could be reversed, etc...)
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