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.