I was thinking about it so I did a real quick and dirty proof of concept. It took longer to take photos, edit, upload yada yada.
This is with 2 layers of tape and a dirty scratched up old lens with a big ugly joint down the center. Normally IMO you'd want the lens turned 90 degrees for headlamp use, I have it like that for taking the picture only.
IMO with a little polish this would be a nice simple mod:shrug: It works better than the photos show- Cell phone camera
Stock
Proof of concept Zebra eye
Like I said quick, ugly I did not even cut the lens straight
Edit:This is where I cut the lens-top is top. I cut there because I wanted to squish the top and bottom of the beam down. I think it went to far though as you can see in the photo. You really should be able to customize the shape of most light beams. Fresnel lenses historically are used for lanterns and lighthouses not sure why we don't see them more in flashlights.