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Comment by hinkley | Hacker News Reader

Why do fresnel reflectors seem to be so hard to find? Seems like they’d be a good option here.

Interestingly, you can DIY that too: http://www.dr-iguana.com/prj_FlatPackMirror/index.html

And I think they really could be a good option. Unlike the lenses, there would be no chromatic aberration with a reflector, right? Plus, you can set the focal length to whatever you want (taking practicality into account of course).

I might have to try it out...

If you could find two parabolic mirrors with a focal length difference of less than a couple of inches, I suspect you could take the middle of the short focus one and the outside of the longer focus one and stack them concentrically, to get a flatter dish.

Honestly for this use case, just sliced and stacked a single dish would give you mostly-collimated light, right? If you put this behind a mild diffuser you could probably still trick your brain unto thinking it's sunlight coming through the curtains.

I wonder this as well, perhaps it's a problem related to manufacturing shrinking sized concentric steps?

If my understanding is correct, fresnel lenses effectively operate as a larger lense surface by concentrating light with flat or curved steps getting smaller in size packed towards the core.

Unless I’m mistaken, you should be able to invert a fresnel lens stamp, make the same plastic lens and then silver it, so now it’s a concave mirror instead of a convex lens.

Do you mean just the lens? There's one in each of those old school overhead transparency projectors. Those should be easy to find.

https://www.bhphotovideo.com/c/product/592006-REG/Dry_Lam_50...

No that's a lens.

A Frensel reflector doesn't led light through bit instead reflects the light. Basically the same idea as the parabolic dish, but as a flat sheet.

Sounds like something you could 3D print.

That was a significant fraction of the links I could find, yes.

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