I discovered these some 4+ years ago when I got a 3D printer. Thingiverse is littered with them and they looked so cool. So, the kids and I printed one up. We waited for the long print, put in a tea candle, and… blurry, wavering, vague shapes on the table that quickly faded to incoherence a few inches from the holder. Not easily daunted after such a long print, we grabbed an LED flashlight and shown it down through the holder and it looked okay. I ran off to my office and grabbed a surface mount white LED (0804) which had been mounted on a small PCB–about as close to a true point source as I can manage. After carefully suspending it at just the rigth point–even a few mm off and the image distorted crazily–we got a decent image with the sharp edges the photos from the article show.
I can’t imagine trying to get a candle that precisely positioned. And evenif I did, it wouldn’t be more than a few minutes before it burnt down enough to be off again.
The problem is the distance between the light source and the holder. If that was larger, then you could use a larger candle and have more ‘sweet spot’ for the illumination. We’re talking something like a foot in diameter, not the few inches these (and the one I printed) were. That might be somewhat practical if also fitted with some kind of height adjustment for the burning taper.
But, that was way larger than my little printer, so we regretfully abaindoned the project.
