I did (note to myself: quit trying everthing you read on ETS).
The material:
- clear ziplock bag 3" x 6"
- lid of CD jewelcase
- 4 clothespins (Iīm aware this is close to cheating)
- tap water

I fill the bag with some water and poured out some until the focal length was manageable. The bag was pinned to the lid with the clothespins. When the bag was filled to about one third I was satisfied. I found that air bubbles are no problem as they rise to the top where the geometry isnīt good anyway. The geometry of the lens deteriorates when it is tilted to the vertical. The focussing is not too good and the intensity is even worse than with the fresnel lens. It gets slightly better when thereīs some water between the bag and the plate (that seems to take care of itself). You have to be really careful to avoid soaking the tinder.
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If it isnīt broken, it doesnīt have enough features yet.