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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?

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JamesRPatrickBest Answer (author)2010-07-08

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.

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Re-design (author)2010-07-09

No.

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.

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steveastrouk (author)2010-07-08

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

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