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Balancing flash with ambient light

By April 19, 2017 Photography No Comments

Introducing the flash in ambient light settings can affect the way we think of camera settings. In particular, while aperture and ISO keep on behaving normally, separate considerations have to be made for shutter speed and how it functions in situations where we could end up using flash.

balancing flash and ambient light

Depending on whether we are using flash in lack or in presence of any continuous light, the shutter speed can either work as a normal sync tool for the flash unit or be the instrument that allows the photographer to control how much continuous light to let into the image.

There are two main situations in which photographers can find themselves using flash:

  1. In a pitch-black environment (only flash light)
  2. In a bright environment (flash plus ambient/ continuous light).

Flash only

For the first scenario, let’s imagine photographing a subject posing in a completely blacked-out studio space using just a single flash pointed directly at the subject. Once you press the shutter button, the flash is only emitted for a very short amount of time before disappearing, with complete darkness being the state that exists before and after the firing of the flash.

In this situation, it makes no difference if the camera’s shutter is as fast as sync speed allows (circa 1/200) or at a much slower speed (such as 10 seconds), as the camera sensor will always only receive the same amount of light: that full burst provided by the flash unit during its brief duration, preceded by darkness and followed by more darkness. In this case, the camera’s shutter speed is not as relevant in the overall exposure of the picture.

Flash + ambient light

For our second scenario, let’s imagine photographing a subject standing in a park under the shade of a tree, with the flash pointed directly at the subject. The subject will mostly be lit by the flash, while the background of trees and sky far away behind them will be mostly lit by the sun (continuous light). From the first scenario above, we now know that shutter speed is not relevant when it comes to flash light, so long as it is at or below the camera’s sync speed capacity. Therefore, changing the camera’s shutter speed will make little or no difference to the exposure of the subject, which is mostly affected by the flash.

Shutter speed does, however, naturally and consistently affect the exposure of an image in continuous light. In this kind of dual-lighting scenario, by simply changing the shutter speed, a photographer can decide how bright the background of trees and sky (affected mainly by continuous light) is going to appear in picture, independently from the brightness of the subject (which is mainly affected by flash and not influenced by shutter speed). In this way, when continuous lighting comes back into play, shutter speed becomes the photographer’s tool to separately operate the two different types of light present in this scenario: continuous and flash. Being aware of this enables us to decide how much ambient light to let into our pictures, whether our intent is to minimise it (with a fast shutter speed) or enhance it (with as slow a shutter speed as we can use). This technique is particularly useful when trying to minimise the harshness of flash light when shooting on location, or even in the studio.

Balancing flash and ambient

Balancing flash and ambient light

In the image above, Ami stood in the shade of a tree but was lit with the direct light of a small handheld speedlight coming around her right side at about 45°. The shutter speed was 1/250, the maximum shutter sync speed that this camera can manage in conjunction with the given light unit. The background of trees and sky behind the model looks dark and the effect of the flash looks very obvious and harsh.

balancing flash and ambient light

This second photo was shot with the a shutter speed of 1/125. Reducing the shutter speed permits more ambient light into the camera, and therefore the shot. By adjusting the shutter speed you allow yourself to control the brightness of areas that aren’t consistently affected by the flash.

balancing flash and ambient light

Examine the difference between the first, second, and third images and you will see the background luminosity consistently changing, becoming brighter as the shutter speed gets slower. The model’s body also slightly enhances in brightness, as she is partially lit by ambient light, but it is mostly the shadows and the background that are affected by the change of settings.

Lowering the shutter speed allows parts of the image not reached by the artificial light to brighten and fill, levelling up with the brightness of the areas hit by the flash. In the final image shot with flash, the light looks much more natural than the first or even the second image thanks to the ambient light that was allowed into the camera to brighten up background and shadows, thereby softening the otherwise harsh effect of the flash. Using this technique, enabled the creation of a pleasant, subtle flash setup with only a small flashgun pointed at the subject, and without any modifiers necessary to enhance the quality of its light. The difference an extra lighting unit can make can be clearly seen in the image below, where no flash was used.

balancing flash and ambient light

All images:
Model: Ami Anselle, makeup and hair: Virginia Bertolani

Lighting People: A Photographer’s Reference is Rosella Vanon’s complete reference and guide to lighting techniques and posing models. Lighting People is an art every photographer—and every photography student—must master, and this single volume is both a complete course and the most useful reference book you can find.

Lighting People, Rosella VanonLighting People: A Photographer’s Reference
Rosella Vanon

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