@ev13wt Hey, it's a time-honored tradition, and one of many reasons lovecpf
@Wacki at the moment, the smallest build I've made or heard of is:
* Your favorite 18650+P60 host (e.g. Solarforce L2)
* 2x AW's IMR18350
* Lumens Forge IMR-9, dealextreme sku.3218, or similar lamp assembly
* aspheric lens to suit your host -- I have used some DX lens for this (don't remember the sku), my last build I used
ahorton's lenses. Whatever fits, with the round side
in and the flat side
out (opposite normal, because we're focusing a parallel beam from the reflector down to a point).
* Optional: a stabbity bezel -- if you're lucky, you'll find one with the points exactly in the focal plane, so you just rest the paper against it. Less lucky, get a long one and sand it down till it
does line up. Or just hold it the right distance manually (you'll soon see the worth of a bezel, then). If you or someone you know smokes or vapes, it can help you see the hourglass shape of the beam, and measure the focal distance.
Now if you'll believe it, I've got a smaller one planned -- using some cylindrical Li-poly cells of the sort used in e-cigarettes, which I finally found a source for (hobby-king). They come in sizes as small as 6mm diameter (tho' 8mm is more interesting to me, as it fits 3-wide in a 19mm bore) and permit 15C drain, so I'm looking at building a slightly oversize 18350 battery that's 11.1V, 180mAh, and good for 2.7A continuous. Naturally, the first and most important role of such a powersource shall be to demonstrate combustion of various materials...
I'm also considering modding a Zippo with a 3-cell pack (could be those round Li-poly, could be flat Li-poly), a WA1166 bulb, and some sorta elliptical reflector to focus the light up top. I'm not sure whether it's actually gonna be hot enough to light a smoke, but I know it'll do paper.