Thursday, April 20, 2017

Lighting 103: Using Gels to Shift the Ambient

Abstract: By combining a white balance shift in your camera with a complimentary gelling of your flash, you can easily and efficiently alter the ambient color temperature of an entire environment.

In addition to controlling the color of light from your flash, gels can also allow you to control the color of the ambient areas of your frame. This can allow you to tweak, enhance or drastically an ambient color environment.

The portrait above, done for the Baltimore Sun, is a good example. I shot him as a storm approached, and the light was gray and pretty neutral.

It was okay, but I wanted a stronger color environment for the photo, and I wanted the guy to pop more. So instead of daylight white balance, I shot it on incandescent (tungsten) white balance. This shifted the expected light source from 5600k to 3200k. In essence, the camera was expecting to shoot under tungsten lights.

But since the ambient environment was closer to neutral (a little cooler, even) the white balance setting had the effect of shifting everything way more blue.

I lit the subject with a single speedlight with a cardboard snoot. The snoot would help me to control the spill of the light form the flash.

To balance my flash's light to my camera's white balance setting, I had to turn it into a tungsten source by adding a full CTO gel. But I did not want my subject to be neutral, I wanted him to be warm and pop out against the blue. So I added another 1/2 CTO to the flash to overcompensate the color and render him in warm light even with the white balance shift.

This warm-on-cool effect makes him stand out, even though he is pretty small in the frame. In addition to being blue-shifted, the ambient is also underexposed between two and three stops. That helps the fully lit (and warm) guy stand out, too.

For comparison, here is a straight (no color shift or gel) lit version:

It's okay, but it doesn't have the color environment that the shifted version does. It's a subjective choice, to be sure. But it helps my guy, bathed in warm light, to pop out from the scene.

Most of the time when we color-shift the ambient using white balance and gels, we do so along the warm-to-cool scale. And it does not have to be a full-on, change to tungsten white balance shift, either. You can use your Kelvin white balance scale to tweak the warmth or coolness of your ambient light as much or as little as you want.

Then you simply counterract that shift with the appropriate complimentary amount of CTO or CTB gel on your key light. And since gels come in calibrated full and partial CTO/CTB units, this is very easy. In essence, with this white balance and gel combo, you can choose your ambient color at will.

It's Like In-Camera Photoshop

But there is no reason to limit yourself to warm vs. cool. You can use a white balance shift and complimentary gel to shift the ambient in any direction you want.

Take the portrait of contortioninst Shelley Guy, above. She is lit against a post sunset sky. I can leave it like that or I could shift the dusk light in any direction I wanted.

Shifting the white balance toward magenta, for instance—and compensating with a complimentary green gel on my flash—I would get this:

In the end, I stuck with the straight sunset. But the point is that we have the ability to shift the ambient in any direction we want, assuming we can gel our flash in the complimentary direction.

Like the Room? Fine. If Not, Change it.

So remember in the last post where we talked about looking at the scene on daylight white balance and seeing what color the room is giving you? If you don't like it, you can change it in any direction you want. Just remember to gel your flash in the complimentary direction if you want to zero out that color shift in our white balance.

With our color-graph indicators in the cameras' white balance controls, and a Rosco CalColor® gel kit, this becomes easy. Just gel your flash in the opposite direction as your white balance shift to compensate.

In the end, the CalColors® are not really so much about coloring your flash as they are about controlling the color of the ambient environment. Use your WB to shift the ambient, then the (complimentary) calibrated gels to bring your flash back as needed.

This technique can save you a lot of flash power, too. For instance, say you are building a night scene and using a lot of blue-gelled lights to establish that feel. Each of those blue gels is gonna cost you a stop or two of flash power, depending on how deeply colored they are. And since you may be lighting large areas with those flashes, they need to be backed up and power will be at a premium.

Instead, flash with white light and shift it all with your camera's white balance. Then use gels to counter-shift the key light(s) to compensate. These lights will tend to be closer to the subject, and can handle the power loss more easily.

A couple of things to remember:

• If you are not getting the saturation you want or expect from a white balance color shift, try underexposing the ambient. As with the photo at top, color shifts become more pronounced when coupled with underexposure.

• To make the subject stand out from the color-shifted background, try overcompensating with complimentary gels on the key light. For example, if shooting in a tungsten white balance setting, try using a full CTO + 1/4 CTO, or full CTO plus 1/2 CTO. That will make your subject warm against the cool, rather than just neutral.

• Or you may wish to integrate the subject into a color-shifted environment, as in the previous post. In this case, try compensating with a complimentary gel—but not all the way. In the scenario above, you might choose just a 1/2 or 3/4 CTO on your key light.


In 50 Portraits, Heisler often uses strong, saturated color in his light sources. But he also will tweak the ambient environment in just the way we are talking about above. Since Greg has done the majority of his work in film, he tweaked the overall scene the analog way—with a physical filter on his lens. He could then compensate with his gelled flashes in the same way described above.

To understand the amount of ambient shift that is being applied, it helps to know the strength of the filters being used. In the double-truck photo of Dale Earnhardt, Jr., on page, 126, that deep blue dusk look was courtesy a Wratten 80A deep blue filter on the lens. A Wratten 80A is the equivalent of a full, daylight-to-tungsten blue shift.

In the double-truck photo of George David, on page 178, a Wratten 80D filter was used. The 80D is a lesser cooling shift than the 80A, as one might do today by tweaking the Kelvin white balance scale on your digital camera.

Either way, the effect was to enhance the color of the ambient environment before applying any flash.

COMING NEXT: Gel Your Lamps

This is the most recent post in Strobist's Lighting 103 module. New installments publish on the first and third Thursday of each month. If you would like to be notified as they become available, please sign up here.

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Time Trap Photography is dedicated to freezing those special moments in life that can be revisited and admired for generations to come. - Shannon Bourque

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