Today's post comes from the book Christopher Grey's Advanced Lighting Techniques: Tricks of the Trade for Digital Photographers. It is available from Amazon.com and other fine retailers.
I’ve written about using a double key light approach several times, both in my Master Lighting Guide for Portrait Photographers and in my columns for shootsmarter.com and prophotoresource.com. It’s such a cool technique that I imagine I’ll write about it again in the future, as I keep finding uses for it and new ways to work with it. If you play with it just once, I’m sure you’ll be impressed by the level of its coolness and will find many applications for it in your own work.
The principle is simple: Use a large softbox (the bigger the better; in this case, I opted to use a 4x6-foot unit), along with another light fitted with a gridded parabolic reflector or beauty bowl (image below). The softbox will provide an underexposed but overall soft light, and the reflector will give the most important part of the image a correct and proper exposure.
To prepare for the first series, I began with a grid-spotted beauty bowl and set both lights approximately 6 feet from where my model would be standing. I placed the softbox behind the beauty bowl, keeping both lights at roughly the same angle. This meant that the softbox (as measured at the height of the strobe unit) would be higher than the beauty bowl when the beauty bowl was centered against it. Think of it as a straight line between both strobe units, because we want the same angle to the light so that we can avoid any possibility of conflicting shadows.
This setup takes a little extra time because both sources must be measured separately, then together. While my model was in makeup, I found the hottest area from the gridspot and measured it with my flashmeter, tweaking the power output from the pack until I had a perfect f/11.
I wanted the softbox light to be two stops under the other light. I turned the beauty bowl light off and sparked up the softbox, changing the power output until it was a perfect f/5.6—two stops less than the other light.
When I switched the other light back on and again metered at the hot spot, I found that the extra light increased the exposure by 1/3 stop (the effects of light are additive), which meant my camera’s effective aperture would be f/13.
Finally, I placed a strip light on a boom, centered directly over the model’s space but about 2 feet behind it to avoid having light spill onto the top of her nose. This light was powered up 1/3 stop brighter than the double main light.
Once you have the position of the lights figured out, it’s a simple matter to make adjustments if you change the position of the gridspot or the softbox: simply turn off whichever light you didn’t move and change the power of the other until you get to the same, original, f-stop. I had to do that for this first shot (image below) because the 25 degree grid threw a light that was too broad at its distance from the subject and the actual effect of the double main light was diminished. I found I had to move the beauty bowl in about halfway, to about 3 feet from the model, in order to get the effect I was looking for—a combination of the two lights that would show both underexposure and perfect exposure on the same subject and location.
Notice how the gridspot forms a gentle circle of soft light that seems to dissolve in from the slightly darker light below. This is the beauty of the double main light setup. You can spotlight your subject but still maintain a great deal of detail in the remainder of her form.
Of course, you can use regular parabolic reflectors, too. For the next shot (below), I removed the beauty bowl and replaced it with a parabolic reflector and a 20 degree grid. I had to re-meter and re-power the parabolic as its light is more concentrated than that of a beauty bowl. When I had achieved my target reading of f/11, my model and I were good to go, and we continued with the shoot. Notice that the background is slightly darker here because the reflector is more narrow. You’ll also note that the circle of light is more tightly defined and the shadows are harder because the light source is smaller.
When your subject wears white or light-colored clothing, you can drop the exposure from the softbox even more than two stops and still retain detail. If your strobes don’t allow linear power changes (and are accurate when making adjustments up or down), you’ll have to turn off the gridspot each time you re-meter the softbox. The exposure from the softbox, for this shot (image below), was dropped an additional full stop to an effective f/4. You will still have to re-meter the two lights together to get a working f-stop because the sum output of the two lights will change.
I switched to a 10 degree grid for the next shot (image below) to show what a narrow gridspot would look like. It’s a look that I personally like very much, and I often use it for senior portraits because my clients like the unusual look as well. I also bumped the power from the softbox down an additional stop, making it four stops below the parabolic. I could tell from my camera’s LCD that the exposure on the background was becoming dangerously dark and would soon be ineffective for this series. The solution was to move all of the lights farther from the background (ahh! the Inverse Square Law at work!). By moving everything farther from the background, the amount of exposure reduction due to falloff was reduced and background detail was maintained. The ratio and spacing of the three lights to the model remained the same.
This double main light technique is something you’ll never see the “fast photo” outlets attempt. They use preset lighting scenarios that, to my eye, look like junk. They are simple, foolproof, and without a spark of creativity. Play and practice with techniques like the double key and you’ll produce results that those practitioners can only dream about.
Please note that your results, based on your equipment, shooting style, etc., will, and should, be different from mine. The amount of reflectivity from the walls of your studio, the size of your studio, and other factors will make a difference in your results. However, the premise is sound and will work beautifully. Your assignment is to make it work for you.
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