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Using Convex Mirrors for Sunlight bounce


Trent Watts
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I don't see how that would even work.

It wont direct light anywhere as the the light hitting the sides will just fall off.


It would be better to just use the standard 4x4 Mirror board in to a 12x12 Ultra bounce/Muslin or whatever or just use a 12x12 rag to bounce light into the area you need.

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  • 3 years later...

We actually had convex mirrors made for “The Northman.” I put an 18k into it to emulate sunlight or moonlight in the studio or outside at night, so I can’t speak about bouncing the real sun. It would be much more forgiving when tracking the sun, and it would put out a pattern more wide and desirable compared to the standard 4-foot flat mirror. However there is substantial light loss with the convex.

For we light snobs, the convex mirror was a very useful tool because it shrinks the source to a proper point, and the “sun” or “moon” starts looking like the real thing. Crisp, believable shadows. To shrink an 18k to the relative size of the sun, we calculated that we’d have to place it over 250 feet away. The convex mirror allowed us to place the lamp 15 feet away from the mirror, and the mirror 30-40 feet from set. You just had to be sneaky about hiding the diverging angle of the rays.

Our mirrors were 1.2 meters wide and 150 or 300mm deep depending on what we needed to do. Light loss was about 3.5 stops with the 300, - you’ve been warned.

-Jarin

Frank: Large silks defeat the mirror of course, and unless your silk is only 4’ wide, you’re only using a fraction of it. Unless you mean multiple mirrors?

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  • 3 weeks later...

I am a bit confused: I would think a "convex" mirror like the one in the first post would broaden the source, making a distant source (the sun...) to appear like a nearby point source. To have a near source appear like a very distant one, I would think one would use a concave mirror, like a parabolic one with the actual point source at its "focal length".

Is there something I did not get, or is just we interpret convex/concave a different way ?

Edited by Nicolas POISSON
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On 4/1/2022 at 4:30 AM, Nicolas POISSON said:

I am a bit confused: I would think a "convex" mirror like the one in the first post would broaden the source, making a distant source (the sun...) to appear like a nearby point source. To have a near source appear like a very distant one, I would think one would use a concave mirror, like a parabolic one with the actual point source at its "focal length".

Yes. That's correct.

Jarin's objective as it appears was to light a large space with a single sharp source. The drawback is that source is objectively closer, which he mentioned about having to hide the "divergent rays."

A parabolic fixture does make the source objectively more distant, creating parallel rays. I don't believe it appears as a smaller source. And it's inherently spotted, requiring more fixtures for a wider coverage area.

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