In that case: use the long summer days to be prepared for the long winter nights! 
Grtz
Nico
Makes perfect sense, go modding when the light's out. Looking forward to the new batch this winter :-)
About me saying 'smart' things, as a biologist and not into physics I only know some basic optics (unlike a few here on BLF who are way more knowledgable than me), but I'm fairly good in thinking those basics through and find a practical use for it in this hobby. And I can not help myself boring the BLF community with that. (As long as it comes with beamshots I think I can get away with that ;-) )
Now now Djozz, no fals modesty please
I personally think you are one of the members truly contributing to this foruym so pls keep it up!
Grtz
Nico
Djozz, I think you have a lot more fans than you think. Like others have said, sometimes I very much enjoy a post, but fail to comment. Usually because I can’t think of something constructive (or witty) to say — other than maybe the overused “awesome.”
So……. “Awesome”, it is.
Oh wait. I just thought of something almost constructive. Did you know almost everybody mispronounces “Fresnel”?
(at least here, in the backcountry.)
“Augustin-Jean Fresnel (French pronunciation: [ɔgystɛ̃ ʒɑ̃ fʁɛnɛl]; pronounced freɪˈnɛl fray-NELL in English) (10 May 1788 – 14 July 1827), was a French physicist who contributed significantly to the establishment of the theory of wave optics. Fresnel studied the behaviour of light both theoretically and experimentally.”
BTW he was born at Broglie. Not many french people know how to pronounce correctly “Broglie”
Two outside beamshots in this thread:
Saw that thread! Wow! :cowboy_hat_face:
I did not seen this thread before. This is very nice experiment with extreme kcd numbers and very nice rainbow beam :)
Wow!
Why was I snoozing on this thread? My perspective on making throwers or search lights completely changed upon reading this. I have to admit though that there are a lot of things I don’t understand also. 
I think I’ll copy this concept shamelessly when I try to build a ‘portable’ ultra long range search light for our rescue team. :bigsmile:
A few tips: measure the focal length of the lens carefully, at a distance as large as possible, and then very carefully make the box with the corect dimensions. My box allows a focal correction of a cm, but that appeared only just enough, more focal travel than that is not a luxury. I was surprised about the focal difference between 20 meter and infinity. Mount the lens as flat as possible (a rigid frame) and stress-free. The finning on the back appeared completely unneccessary for an XM-L2 at 5A.
Does it have a moonlight mode and does it come with a pocket clip? 
Thank you for the tips djozz! I will keep that in mind.
I am going to build something like this with an CXB3590 @140 watts
though I need a collimator lens right in front of the COB to narrow the spread of it, I got a 90mm diameter and 90mm focal length lens so far but that is not enough, I will need a near (half)sphere to get a narrow enough beam of the COB for my fresnel.
I see, so you are going for maximum output in your build. I have asked myself that, more light is more useful but smaller light sources (less light) give a more intense hotspot. I’m still debating if I should rebuild the light with a Cree XHP70.2 for more light and still a pretty intense hotspot.
the collimator should compensate for the die size, it would make it look like a 3x3 mm LED from the focal point of the fresnel, which is pretty small, given lens loses and spill there should still be >60% of the LEDs light remaining.
I was also thinking about using a fresnel mirror to narrow the COB…
glad to see this thread revived, I missed it on the first lap. Nice build! I really like the speaker box megathrower. I have a smaller fresnel that I have been playing with and have been tempted to grab a free projection tv off craigslist or kijiji to salvage the ~60” fresnel out of to have some fun.
You want to use the spherical lens as a pre-collimator (mounted right above the LED)?
Then it’s the other way around. The apparent size of the LED as seen from the main lens is enlarged (probably doubled).
That’s not how it works.
The apparent size of the spot will depends on the diameter of the led and it’s distance from the FIRST optic.
If you have the LED 90mm away from the first lens, it will be a much higher divergence beam than if it was 1m away from the large fresnel lens (or however long that focal length is).
What the precollimator does is increase the luminous efficiency by collecting a higher percentage of total flux (lumens), while simultaneously creating a larger spot.
I may have said this before in some related thread. Light spreads outwards in a wide angle range from the led by design. I believe you should build a triple lens setup for maximum throw:
- A powerful über short focal distance precollimator, also with enough size to lose as little light as possible. Output: a wide straight cone of light.
- Another collimator: the concentrator, another plano-convex style of lens rotated 180° with respect to the precollimator. Output: the cone of light re-concentrates to a point of light (or sort of) at focal distance. Diameter of this lens should match precollimator.
- Diverginator: the final focusing diverging lens, concave sort, which at the correct optimal distance from the concentrator would create a very tight cylinder/cone of light.
Mmmkay, now I'm gonna shut up and go see if some sort of trampy lass asks me for love services btw. 
Minor influences of lens systems ignored, throw depends on the diameter of the largest lens, in this case the fresnel. Whatever number type or position of lenses you throw at the system may affect many parameters but hardly the throw.