Convex Mirrors Part I: Augmenting Natural Light

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augmentation
Convex mirrors are amazing tools for lighting a scene. The easiest way to understand what they can do is to think of them as short focal length lenses for light – they have the same characteristics of deep focus, diminished object size and exaggerated distance.

Like all mirrors, they have other advantages: bouncing light from a mirror (especially a small one) makes light control simple and quick. The shape can be quickly changed with a strip of paper tape and there is zero spill unless you want it. The light not reflected by the mirror can be negated, used as general fill, directed by small highlight mirrors or any combination of those – without wrestling flags, floppies or half a dozen stands. Finally, a well placed mirror has nearly no footprint so light can be brought from directions or angles that might not be possible using a lamp directly.

The effect used above is often done with an HMI pushed through a window, but a source like that can be a real pain to shape. I didn’t want this effect to overpower or spread the natural light, just punch an effect into it. Moreover, if you’re shooting on the 3rd floor, don’t have access to power outside, are in the middle of a tropical storm (or 15 below zero) or are just without tall stands – you may have some challenges pushing in from outside. In the shot above, the effect was achieved inside the room, only 7 feet from the mirror to the wall. The light is also perfectly positioned to match the natural light through the window.

It’s basically the same configuration as in Return of the Venetian Blinds: light–>mirror–>cookie–>target but in an even more compressed setup. There’s barely a foot from the light to the mirror, only 22″ from the mirror to the cookie and 7′ from the cookie to the wall. Tiny. I’m using my Altman 65Q – the best possible light for this kind of work – and a stick-on rear view panoramic mirror for a convex mirror. It looks like this in its DIY foam core portfolio case:

case2

This is the curvature of the same mirror, just barely enough to allow a number 2 pencil to get underneath it:

curvature1

I regret to confess I do not have precise data on optimal mirror curvature for this kind of work. But, I have plenty of observations and experience. What you need to know is this: beyond the amount of curvature in a normal ‘panoramic’ rear view mirror, the losses outweigh the gains. It takes very little ‘wide angle’ to get naturalistic effects. With every degree of curvature beyond that we lose dramatically more light.

Here’s an example. This is the room with only naturally occurring light:

scene-natural

This is the room using the panoramic rear view mirror as a source:

scenepanorearview

This is the room using a slightly more convex mirror and no other changes. You could call it ‘subtle’:


scene-smallrearview
 

The setup was very simple. My Altman 65Q uses a 750W lamp and I have it gelled to one full plus one half CTB to match the very wintry light coming in through the window. The mirror is about 12″ from the light, the cookie is a piece of window dressing picked up in a salvage yard with some fake miniature ivy found in a thrift store. The mirror/foam core backing is held by an articulating arm anchored on the light itself the cookie/ivy are held by a 2nd C-stand.

 

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