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Are umbrellas parabolas? Answered

I am trying to make a homemade spotlight and I need a parabolic reflector. Instead of sketching one out on my own (which I'm only semi-confident I can do correctly), I thought it might be possible to use an umbrella coated with tin foil as a reflector. I remember reading that they were parabolic somewhere, but I can't remember where I read it. Are they parabolas?


Um, well umbrellas come in hundreds of styles, but they consist of several segments that would make a light source go in a bunch of different directions. I'd look for some kind of wok or other stainless steel cooking dish.


Here is a drawing of a parabola.  You can see that it is deeper than an umbrella.

Photographers use umbrellas that are reflective on the inside to reflect a strobe.  But they are not using it for spotlight purposes.  It actually smooths out the light.

They aren't generally paraboloids. You might be able to distort one into the right shape though. Steve