Friday, July 6, 2012

Lighting glass against a dark background

To make this kind of shot work, you don't need an expensive camera or lots of lighting equipment.  What you do need is plenty of space, many black and white reflectors (I use poster board) along with convenient ways to position them, and a fair bit of patience.  A long lens also helps, but isn't essential.

Dark-field lighting -- refraction is your friend

The chief problem with photographing a glass subject like a wine bottle or stemware against a dark background is that the glass tends to blend into the background, so you can't tell when the subject ends and the background begins. In Light Science and MagicFil Hunter, Paul Fuqua and Steven Biver show how to address this challenge using what they call dark-field lighting.

Dark-field lighting makes use of the fact that when a ray of light strikes glass or any other transparent subject at an angle, it bends.  You may recall from high school physics that this property of light is called refraction.  It's what allowed Isaac Newton to construct the first prism, and it's essential to photography.  Without it we wouldn't have lenses. 

The idea of dark-field lighting is to light the subject against a dark background while using refracted light to define the boundary of the subject.  To accomplish this, you light the area behind the subject just outside the dark background and frame the shot so that only the dark background is visible to the camera.   As illustrated in the diagram below, the light from behind the subject will be refracted as it enters the edge of the glass.  Even though the lit part of the background is not visible to the camera, some of the light refracted through the glass will be visible.  This refracted light defines the outline of the glass against the background. Refractions through a transparent subject are most visible when the light striking it comes from as close to directly behind as possible.  This means that if you've got the room, you're best off getting a lot of distance between yourself and the subject and using a long lens to fill the frame.

You can never have too many flags

Although the idea of dark-field lighting is to frame the shot so that the camera cannot see the light coming from around the dark background, if you try this technique yourself you'll quickly find that glare from your back light tends to reduce image contrast and create an unwanted halo around the perimeter of your frame.  To minimize this, I recommend positioning flags between your subject and your camera to shade the lens from your light.  These flags should not, of course, be visible in your frame.  The best color for these flags is black, so that they aren't reflected in your glassware.

Manage reflections

If you're only lighting the subject from behind using the dark-field technique with black flags in front, you'll produce a lovely outline of the subject, but you may not be able to see much else.  To illuminate the front of the subject, you can try using a separate light source, but you'll have to be careful to avoid hot spots reflected off the glass.  Since you've already got light coming from behind the subject, I suggest experimenting with white reflectors before bringing in additional lights.  A white card or two positioned in front of the subject can produce simple reflections in the glass that help to define its shape and surface texture.  

This photo up top was lit with a single flash fired into a white wall behind the black card which serves as the background.  A white card in front camera left provides the rectangular highlights in the glass and bottle.  It also helps to illuminate the label.  Black cards to the left and right of the camera were used to flag off glare from the lit back wall.

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