Controlling Light in Photography. Part 1

Controlling light in Photography – The term "photography" comes from the Greek "phos", meaning light, and "graphis", which means to draw or write. Photography can be defined as "the art and science of altering images on a sensitive surface through action of light". We see that there is at least in principle, some understanding of the nature of light and how to control. Which is fundamental to one's success as a photographer.

The Behaviour of Light

In Part 1 of this article, the behaviour of light which concerns the portrait photographer is addressed.

We shall begin to explore methods used by portrait photographers to control the behaviour of light. Especially when rendering artistic interpretations of their subject, living or otherwise. There are many aspects involved when manipulating light for the purpose of portrait photography.

One fundamental aspect is always exposure. The degree of sensitivity of light (photo-sensitivity) on the surface to which an image is to be fixed. Whether film or digital, it dictates the required intensity and length of exposure.

The Aperture

The aperture of most lenses is designed to allow control over the intensity of light falling onto the film or sensor. The aperture is basically a hole or opening through which all light reflected by the subject is admitted into cameras.

The intensity of the reflected light being allowed to expose the film or sensor is mostly controlled by the size of this opening.

The size of the aperture opening or hole is commonly regarded in f/stops. F/stops can seem confusing at first. The f/stop numerical value represents a fractional opening of the aperture in the lens. So a decrease of one f/stop actually results in the intensity of light being admitted or allowed into the camera to approximately double. So an increase by one f/stop will result in the intensity of light being cut by half.

One may prematurely conclude that proper exposure is simply obtained by adjusting the size of the opening or aperture. Until the intensity of light admitted in is just right.

However, the depth of field or DOF is also a useful function of the size of the aperture opening. DOF is the range of distance both in front of and behind the subject which is in focus.

In general, depth of field or DOF increases as the size of the aperture opening decreases and vice versa.

Shutter Speeds

Controlling the exposure is also achieved by adjusting the duration of the light hitting the film (or image sensor). To control the length of the exposure, most modern cameras employ a shutter. The shutter may be thought of as a metal curtain with an opening. A slit that passes in front of the film (or image sensor) at a pre-controlled duration or speed.

Shutter speeds are expressed in minutes, seconds and fractions of a second.

So, a shutter speed of 1/100th of a second allows twice the duration of exposure as a shutter speed of 1/200th. The resolution of an image is in part, determined by the length of exposure in capturing the image.

A standard approach in portrait photography is to set the aperture size to give the desired depth of field. Then to set the shutter speed to obtain an acceptable exposure level.

The ISO

The third fundamental parameter that is adjustable when controlling exposure of an image is the film speed (or ISO/ASA number). Film speed is a quantitative description given to the "chemically derived" photo-sensitivity of any material used in the film.

The higher the ISO or ASA number, the more photosensitive the film or sensor is. Faster film speeds will enable quick action shots and low light images to be more easily captured.

However, faster film speeds normally also result in increased graininess or "noise" in an image with decreased sharpness and detail. Similarly, the ISO or ASA number on most modern digital cameras can be adjusted to manually control the sensitivity of the digital image sensor, with a similar effect.

All light is controlled from within the camera by manipulating the duration and intensity of exposure, and by choosing an appropriate film speed for the light conditions at hand, or by adjusting the sensitivity of the digital image sensor.

These methods will work very well to control the overall or average exposure of the composition.

For a finer degree of controlling light in photography to enhance spectacular highlights, falloff, and softness of shadows, this is best achieved from outside the camera.

There are many methods used to accomplish this. In Part 3 of this article, several such methods will be discussed. Until then, have a good day and happy clicking.

Related Products for Controlling Light in Photography

Breakthrough ND Filters - Great for reducing light from 1 to 6.6 stops in one filter! Breakthrough are the best you can get for image quality and accurate colour representation. I use them all the time.

Circular Polarizer Filters - A must have for photographers of all levels! If you don't know what they do, check out our article on using filters.

About the Author: Steve Barnes is a professional portrait photographer, freelance writer, and co-owner of Hayley Barnes Photography, in League City, Texas.