Sample chapter from ...

Getting Serious About
Photography

A Self-Paced Workshop for Expanding
Your Photographic Skills and Vision

a how-to book by
Ernest H. Robl

Please Note: The entire work from which the following material is excerpted is protected by copyright. None of the content may be reproduced in any form without the express written permission of the copyright owner.

Copyright © 1998 Ernest H. Robl, All Rights Reserved

LIGHT, Part I: Seeing

Photography means writing with light. Without light, there's no photography. It's a simple as that.

But it's also complicated in that we need to be able to understand the characteristics of light that can affect our photographs.

Light has both quality and quantity, and both are important to us. In the first case light can be either warm or cold or it can be soft or harsh. Quantity can be equated with brightness. We need a certain quantity of light to be able make photographs at all.

Both quality and quantity can be measured—at least to a degree. But, understanding how these factors affect our photographs can be more important than the precision with which we can measure them. And, both factors can be managed. Before we can learn to manage them, however, we need to understand them.

Let's start with the quality of light. What do we mean by saying that light is warm or cold? First, these descriptions have little to do with the ambient air temperature.

They're a method of describing the color of the light. A golden sunset has a warm glow. And, ironically, the hot mid-day sun produces light that is actually much bluer (cooler, in our way of describing light) than that at either end of the day, a fact that's even more noticeable if the subject we're observing (or photographing) is completely in shadow and not receiving any direct illumination from the sun.

Then, there's the perceived softness of light. That's really a way of describing the contrast with which our subject is illuminated. Mid-day with clear skies produces very contrasty illumination—brightly illuminated areas receiving direct sunlight and dark shadows. (Of course, the darkness of shadows is relative. On a bright summer day, an object in full shadow—with sunlight being blocked by a building or tree—may actually be more brightly illuminated than a similar object on a somber winter day.)

Add a hazy overcast, however, and shadows will begin to soften or even disappear. The contrast range between objects and their shadows—providing both have the same intrinsic color and brightness—will decrease greatly.

Taken together, these factors can determine the mood of a scene—or of a photograph. Soft, warm lighting can be romantic; cold, harsh lighting can be dramatic, for example helping to delineate architectural features, but is hardly flattering to a person depicted in that light.

The quantity of light, on the other hand, also has more effect than just determining whether or not we can make a photograph in a given situation. It will affect such things as exposure and depth of field. It may determine the type of film we can use in a given situation, because different films have different sensitivity to light.

In that one brief paragraph we've opened a can of intertwined worms that define some of the more difficult problems of photography.

This is getting complicated, I hear some of you saying. Yes, and no. Some of that complexity will go away over time—not because we no longer have to deal with these items, but because dealing with them will become automatic.

A new driver worries about pressing the accelerator and how far to turn the steering wheel; an experienced driver still has uses the same tools to control his car, but he no longer thinks about the individual actions—only about where he is trying to go.

So, how do we begin to unravel these complexities? By talking a little about exposure and by pretending that light is a blob. That's right, for the purposes of this discussion, light is a blob. (I know that it isn't and you know that it isn't, but pretending that it is will help us to understand exposure.)

Where do we start for exposure? With the film. We'll talk much more about film later, but for now, all we need to know is that photographic film is coated with a layer (the emulsion) that is sensitive to light. When that emulsion is exposed to light the chemical structure of the emulsion is affected. If that exposure to light was in the form of an image, focused onto the film by a lens, an invisible (latent) image is formed.

Treating that emulsion containing the latent image with other chemicals turns that latent image into one that we can see—either a negative (an image in which light and dark and colors are reversed from what they are in nature) or a positive such as a slide. We call that processing or developing the film.

See, we've already learned a little useful terminology. That wasn't so painful, was it?

Now, there's a lot more going on behind the scenes, of course, but we no more have to understand all the chemical processes to be able to make photos than we have to know about everything that happens under the hood in order to drive a car.

Each film also has many characteristics, including particular sensitivity to or the ability to reproduce certain colors. There's also something called grain, which is usually related to the film's ability to record detail. And, films, like the light they record, can be either contrasty or soft; either warm or cold in rendering colors.

Aha. I can already see the lights going on in some of your heads. We can use the characteristics of films to either enhance or counter-act characteristics of subjects that we are photographing. A warm, soft film used to record a scene with warm soft lighting will enhance the mood of the scene; using the same film with its warm low-contrast bias on a contrasty scene with cold lighting will help to minimize the latter effects.

You're absolutely right. We'll look at some of these features in more detail in another chapter. But, for now, we still need to deal with the fundamental problem of exposure: How much light does a particular film need and how do we control that amount?

Every film has a specific sensitivity. There are international standards for determining that sensitivity. (You don't have to do that; the manufacturer has already done that for you.) That sensitivity is shown as the ISO rating (ISO stands for International Standards Organization) on the film box and film cartridge.

If we know the sensitivity of a film, we also know how much light that film needs in order to produce a correctly exposed image. Now, it's up to us to control the existing light so that just the right amount of light reaches the film. No more, no less. That's the exposure.

Now, obviously, a key factor is the ability to determine how brightly lit our subject is. In other words, we need to be able to determine the quantity of light that we have to deal with.

Are you with me so far? Good. We measure the quantity of light with a device called a light meter. Most modern cameras have one of these built in, but there are also hand-held units that can serve important functions in special situations. We'll devote one of our Hardware discussions later just to light meters. For now, all we need to know is that it is possible to use one of these devices to measure the quantity of light.

Now that we know how much light the film needs and how much light there is, all we need to do is to control the amount of existing light that reaches the film. (Yes, we can even add to the existing light, if necessary. And, we'll talk about that, too.)

So, here comes Ernest's "light is a blob" analogy.

Think of light as a blob that is attempting to flow at a given rate towards your film. (Think of it as going downhill with gravity, if that helps, though, of course, there's no gravity involved here.)

Think of the lens as a pipeline directing the light toward the film. Think of the camera's shutter as a valve that turns the flow through the pipe on and off. In fact, think of it as a valve with a timer that controls how long the valve is open.

Blob. Pipe. Valve. Clear so far? Good.

Leave the valve open for 1/125 of a second, and twice as much light gets through the pipe as when we leave the valve open for a 1/250 of a second. These are our shutter speeds.

But, exposure time is only one control. What if we were able to vary the diameter of the pipe? A larger pipe would transmit more light during the same amount of time; a smaller pipe less. And, that's just what the iris diaphragm (also called the adjustable aperture) in the lens does. (The pupils in our eyes do the same things. They close to a smaller diameter in bright light and open up to admit more light in a dim situation.)

The light transmitting power—pipe diameter in our analogy—is measured in something called f-stops. (That's because the measurements are related to the focal length of the lens. Focal lengths are something else we will worry about later.) For now, all we need to know is that on any lens, a given f-stop will transmit the same amount of light to the film.

F-stops are usually marked in the following increments: 1.4, 2.0, 2.8, 4.0, 5.6, 8, 11, 16, 22, 32, 45, where each following step transmits half as much light as the preceding one. That's right: The lower the number, the more light the lens transmits. (Not all lenses will have the full range shown above.)

Maximum apertures are an important characteristic of lenses. A lens with an f 1.4 maximum aperture is considered a fast lens, because, when set to its widest aperture, it transmits a lot of light. A lens with a maximum aperture of only f 4.0 or f 5.6 would be considered a slower lens.

Consider that for two lenses, both being used at their maximum aperture, but one having a maximum aperture of f 1.4 and the other a maximum aperture of f 5.6, the slower lens would require 16 times as much light to be present to use the same shutter speed (duration of the shutter being open).

How did we get that? Simple, by multiplying by two each time we go to a smaller stop: f 1.4 to f 2.0 is a factor of two (doubling). Going down four stops is equivalent to 2x2x2x2 or 16.

Shutter speeds conveniently are also arranged in increments where going in one direction doubles the amount of light; going in the other halves it. A typical range of shutter speeds on a camera may include the following: 1 second, 1/2 second; 1/4 second; 1/8 second; 1/15 second; 1/30 second; 1/60 second; 1/125 second; 1/250 second; 1/500 second; and 1/1000 second. (Some professional-level cameras with modern electronics can also accurately open the shutter for durations of as little as 1/8000 of a second or for exposures of multiple seconds.)

Now, getting all of the above on a scale or display would take up a lot of space, so, for the sake of brevity, usually only the divisor is shown. So, the scale looks like this: 1; 2; 4; 8; 15; 30; 60; 125; 250; 500; 1000.

The way that works out again, is that the bigger the number on the scale, the shorter the exposure.

Now, consider that to get a given amount of light through the pipeline, there are many possible combinations of shutter speed and f-stop—but for any given f-stop or shutter speed, there is only one corresponding unit of the other.

For example, on a typical bright sunny day, for a film with an ISO rating of 100 (a fairly typical average film widely available today), our light meter (also called an exposure meter) may indicate an exposure of 1/125 of a second with an f-stop of f 16. That would mean that all of the following combinations would be valid:

What these choices mean to us, and why none of the above may be the right choice for this situation are the subject of the next session.

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