Intro to aspheric lenses (to help you choose the best one)

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Humpers
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Re: Intro to aspheric lenses (to help you choose the best on

Post by Humpers » 21 Jan 2013, 22:21

Marky610 wrote:The BFL I found with and Ant supply lens are as follows................

50mm = 32mm
66mm = 42mm

Stick that in your calculator's :mrgreen:
Thanks Marky, done.
IR LED & aspheric lens comparison table, v2.jpg
IR LED & aspheric lens comparison table, v2.jpg (77.22 KiB) Viewed 744 times
Although sadly I've not seen either, from what you've said about the usable range of your 50mm and 66mm Markylights I'm coming to the conclusion that the tighter beam from the longer BFL 66mm lens (due to the longer BFL allowing the LED to be more like a single point source) is the key to longer ranges. That is provided the lens is wide enough to capture a reasonable amount of the light. What do you reckon from all your practical experience?

If that's the case the die size may also have an influence. I'll add that info to the table when I've got time in case it prompts any further ideas about which LEDs it may be worth experimenting with.

Humpers

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Marky610
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Re: Intro to aspheric lenses (to help you choose the best on

Post by Marky610 » 21 Jan 2013, 22:51

So in theory the A Horton lens should be brighter and throw further than the 66mm?

I have one, shall i knock one up and test the theory? I could do it tomorrow and test it tomorrow night ;)
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phoenix
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Re: Intro to aspheric lenses (to help you choose the best on

Post by phoenix » 21 Jan 2013, 22:54

Humpers,
I've been looking at the specs for that Vishay IR LED and I think that rather than using radiant intensity (mW/Sr) as a measure of how well the LED will work with an aspheric lens it might be better to use the radiant power figure (mW) and calculate the percentage of the total radiant power which actually enters the lens for any of the LEDs when placed at the focal point of the lenses you have listed.
For example, the Vishay LED has a radiant intensity of 500mW/Sr (which is high) but a total radiant power of only 50mW (which is very low).
Even if if all the light from the LED hits the lens, there will still only be 50mW of optical power available to produce the beam.
Compare that with the Oslon and the ANT supplies 50mm lens where 70% of the light hits the lens. The radiant power of the oslon is 1070mW, so 70% of that is 749mW of optical power available to produce the beam.
For the Dragon, the radiant power is 530mW and 84.8% hits the 50mm lens giving 450mW of optical power available for the beam. This would suggest that the Oslon is better than the Dragon - and I think that's been shown to be the case in practice (Osram have discontinued the Dragon)
Using the same method, the Ostar hits the 50mm lens with 1876mW and the LedEngin with 1492mW and therefore these would appear to be much better than the oslon..
However, the ostar and the LEdEngin use multiple emitters which don't act nearly as well as a point source as the oslon.
The multiple emitters spread out the light source and a fair bit of their power is wasted.
I personally have tried an Ostar and oslon next to each other with identical 50mm aspheric lenses and the oslon produces a better beam and uses a lot less power (and costs about 1/10 the price of an ostar)

Cheers

Bruce
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Marky610
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Re: Intro to aspheric lenses (to help you choose the best on

Post by Marky610 » 21 Jan 2013, 23:15

Sorry just thought, my measurements are to the star as they are for construction therefore the actual BFL is probably a couple of millimeters less :oops:
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Re: Intro to aspheric lenses (to help you choose the best on

Post by johnnyrebel » 21 Jan 2013, 23:39

Best thread on the net lads, absolutely 'kin brilliant. So much info... too much for me to absorb tonight. Well done! :thumbup:
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snoopy
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Re: Intro to aspheric lenses (to help you choose the best on

Post by snoopy » 22 Jan 2013, 00:44

cool :thumbup:
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some bloke
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Re: Intro to aspheric lenses (to help you choose the best on

Post by some bloke » 22 Jan 2013, 01:22

This is an absolutely spiffing thread that warrants a place of honour in our illuminator section sticky pages - in my opinion. :thumbup: :clap:

I'm especially very pleased with the Ahorton lens results because although I categorically know they are better than the DealExtreme ones (similar thickness to Kaidomain's) I just couldn't for the life of me fathom why. I have only compared them using a cheap ebay 1 watt LED that looks to have a slightly larger size die to the Oslon Black though. The DX ones are more than capable for FAC air ranges and I now have realistic feelings that the Oslon would extend that to at least moderate rimfire range, so lens choice could be used to match them to the application perhaps.

Nobbybonez has compared the Oslon Black as better than the Dragon in a P60 drop-in module, both drop-ins manufactured by nailbender on the Candlepower forum if it helps anyone.
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Re: Intro to aspheric lenses (to help you choose the best on

Post by AirRifleSport » 22 Jan 2013, 01:56

Top post and well explained. :thumbup: :clap:
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rodp
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Re: Intro to aspheric lenses (to help you choose the best on

Post by rodp » 22 Jan 2013, 08:22

Humpers wrote:
rodp wrote:If you work it out the 50mm Ant Supplies at app 35mm focal length captures all the half angle of the Olson Black. I think with a 50mm lens the perfect half angle BFL should be 35.36mm, so it captures just over that.
A shorter BFL would capture even more it appears and it seems a shame to waste it :lol:
I'm impressed that someone else has done some maths.

You're almost right that it captures all of the half angle. BUT that's the problem, it's ONLY capturing the beam out to about the half angle, which is only about 81.5% of the LED's total output. Nearly 20% the photons beyond the half angle are escaping outside the edge of the lens so are being wasted.

And remember that the 50mm lens only has 46.7mm of usable lens, so I think the perfect half angle back focal length is closer to 33.7mm, meaning that as the actual BFL is 35mm even some of the beam within the half angle is being wasted. Hence only 66.2% of the photons are being captured.

If I've got my maths wrong then please do tell me before I embarrass myself further!
I think you've made the same mistake as I did. I had the reflector on my mind whilst working it out and didn't take into account the ideal bfl for the half angle being at right angle to the lens, the 33.7mm (I make it 35.4 now :? ) is actually the reflector (at 45* to the lens).
If the lens was 50mm useable area the bfl (being at a right angle to that) would be half if it was to capture all the half angle.
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Re: Intro to aspheric lenses (to help you choose the best on

Post by philcbr » 22 Jan 2013, 10:36

Humpers,
Top post, well done fella :clap:
Phil

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