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Bill Hurter

Flash-Fill and Flash-Key

By Bill Hurter
Published by Amherst Media

How do you determine accurate fill-flash exposures every time or use your flash as a key light? Bill Hurter explains in this excerpt from his Wedding Photographer’s Handbook from Amherst Media.

This excerpt from Wedding Photographer's Handbook is provided courtesy of Amherst Media. To purchase the book and learn more about the publisher, visit the Amherst Media Web site.

A predictable form of shadow fill-in is electronic flash. Many photographers shooting weddings use barebulb flash, a portable flash unit with a vertical flash tube, like a beacon, that fires the flash a full 360 degrees. You can use as wide a lens as you own and you won’t get flash falloff with barebulb flash. Barebulb flash produces a sharp, sparkly light, which is too harsh for almost every type of photography except outdoor fill. The trick is not to overpower the daylight. It is most desirable to let the daylight or twilight backlight your subjects, capitalizing on a colorful sky background if one exists, and use barebulb flash to fill the frontal planes of your subjects.

Some photographers like to soften their fill-flash, using a softbox instead of a barebulb flash. In this situation, it is best to trigger the strobe cordlessly with a radio remote trigger. This allows you to move the diffused flash out to a 30- to 45-degree angle to the subjects for a dynamic fill-in. For this application, it is wise to equal or overpower the daylight exposure slightly so that the off-angle flash acts more like a key light, establishing a lighting pattern. For large groups, it may be necessary to use several softboxes or to use a single one close to the camera for more even coverage.


A handheld incident flashmeter is essential for work indoors and out, but it is particularly useful when mixing flash and daylight. It is also helpful for determining lighting ratios. Flashmeters will prove invaluable when using multiple strobes and when trying to determine the overall evenness of lighting in a large room. Flashmeters are also ambient light meters of the incident type, meaning that they measure the light falling on them and not the light reflected from a source or object. 

Metering and Exposure for Flash-Fill

Here is how you determine accurate fill-flash exposures every time: First, meter the daylight with an incident flashmeter in “ambi” mode. Say, for example, that the metered exposure is 1/30 second at f/8. Next, meter the flash only. It is desirable for the flash output to be 1 stop less than the ambient exposure. Adjust the flash output or flash distance until your flash reading is f/5.6. Set the camera to 1/30 second at f/8. That’s it. You can set the flash output from f/8 to f/5.6 and you will not overpower the daylight; you will only fill in the shadows created by the daylight and add sparkle to the eyes.

Daylight was the main light source for this charming image by Noel Del Pilar. To get a sparkle in the bride’s eyes—and good modeling on her face—Noel used a small, diffused strobe held high and to the left of the bride. The strobe was about ½ to 1 full stop brighter than the daylight in order to overpower it slightly.

If the light is fading or the sky is brilliant and you want to shoot for optimal color saturation in the background, overpower the daylight with the flash. This is where the flash becomes the key light and the ambient light becomes the fill light. Returning to the situation above, where the daylight exposure was 1/30 second at f/8, adjust your flash output so your flashmeter reading is f/11, 1 stop more powerful than the daylight. Set your camera to 1/30 second at f/11. The flash is now the key light and the soft twilight is the fill light. The problem with this technique is that you will get shadows from the flash. This can be acceptable, however, since there aren’t really any shadows coming from the twilight. As described previously, this technique works best when the flash is diffused and at an angle to the subjects so there is some discernable lighting pattern.

It is also important to remember that you are balancing two light sources in one scene. The ambient light exposure will dictate the exposure on the background and the subjects. The flash exposure only affects the subjects. When you hear of photographers “dragging the shutter” it refers to using a shutter speed slower than X-sync speed in order to expose the background properly.

One of the ways to deal with unflattering sunlight or overhead open shade is to overpower it with strobe, as was done here by Nick Adams. By overpowering the available light by about 1 stop with the assistant-held strobe, he created a pleasing portrait lighting pattern on the couple. The daylight became the overall fill light. The strobe was held high and to the couple’s right and it was fired remotely. The exposure was 1/160 second at f/4. Nick vignetted the image in RAW file processing.


Category: How-To
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