Lesson 1 - Exposure Basics

Alright, let's start at the very beginning... Exposure. Now, this may seem a bit tedious, but stick with me. We'll get to the fun stuff, but you've got to learn the basics first!

What is a photograph? In it's simplest definition a photograph is a record of light. We use cameras to capture and record light. That's it... light! Sounds simple enough, right? It's unfortunately not.

Our input is light, plain and simple. Our output, or what is actually produced when we record that light on a piece of film (or on a digital sensor) is called an exposure. Side note: the terms "film" and "sensor" are, for the most part, used interchangeably on this blog. I will talk mostly of digital sensors and DSLR (digital single lens reflex) cameras.

So, just like any other created (and recorded) material we have: input > capture device > output. In our case: light > camera > exposure

There are two basic elements to a photographic exposure on film or a digital sensor. They are intensity and time. Exposure can thus be represented by the following formula:

Exposure = Intensity x Time

[E=I x T]

Where intensity represents the amount of light that falls onto the sensor during exposure and time represents the duration (measured in seconds) for which the shutter of the camera remains open. So to put it another way:

Exposure = amount of light X the duration for which that light is recorded

Now let's look at what controls these two variables:

Aperture

Intensity is controlled by the lens aperture. The aperture is the actual size of the opening inside of the camera lens that controls the amount of light passing through the lens and ultimately landing on the film, and is referred to as the f-number, or f-stop. Aperture is adjustable and can range from 1.0 (the largest opening) to 90 (the smallest opening) (yes, the numbers get bigger as the actual size of the hole gets smaller), although working apertures usually range from 2.8 to 22. Aperture also controls depth of field, which we'll discuss later. When you press the shutter button to take a picture the lens closes down to the set aperture, the shutter opens and closes, and the aperture opens back up. This happens almost instantaneously. We'll talk much more about aperture later.

Shutter Speed

The duration of the exposure is measured in seconds and most often fractions of a second. There is only one shutter speed that will correspond to a given aperture (and given film speed, or ISO) in order to attain a proper exposure (and vise versa). In other words, if you have a proper exposure, but want to change either your aperture (intensity) or your shutter speed (time), you must find an equivalent exposure. Remember our formula: E=I x T

Equivalent Exposures:

If you, for example, find that you have a proper exposure (enough light falling on the film or sensor in order to produce an image that is neither too dark nor too bright - example 1 below), but the shutter speed you are using is too slow and is causing unwanted blur you can open up the aperture in order to speed up your shutter speed. If done correctly, this will allow you to retain the same exact exposure while at the same time getting rid of unwanted motion blur.

Example 1 - What is a "proper exposure?"

Let me explain a little further. A change in shutter speed is going to require an equal change in aperture in order to attain an equivalent exposure and vise versa. If you want to speed up your shutter speed duration, you must increase the diameter of your aperture, thus letting more light in (higher intensity) so that your faster shutter speed (shorter time duration) will still give the film enough light for a proper exposure (E=I x T). Here's where it gets confusing. When the aperture opens (to let more light in) the f-number gets smaller (f/2.8 is a much bigger opening than f/16).

This is a good way to remember equivalent exposures:

Speed up, Open up... Slow down, Close down.

When you speed up the shutter, say from 1/250 of a second to 1/500 of a second (letting 1/2 as much light in due to duration), you must open up your aperture from, say from f/16 to f/8 (letting twice as much light in due to an increase in aperture size - We'll get to this later). These two changes cancel each other out and you are left with the same basic exposure. Going the opposite direction if you were to slow down from 1/500 of a second to 1/250 (letting twice as much light in), you would need to close down, or "stop down," the aperture from f/8 to f/16 (letting 1/2 as much light in). Confused yet? It's okay, you should be, especially if you're a beginner! Just try to wrap your head around the whole "Slow down, close down... Speed up, open up" theory and try to actually visualize that aperture opening getting smaller as you close down (f-number increases) and getting larger as you open up (f-number decreases).

Here's an diagram to help you visualize that aperture opening with a corresponding f-stop

Well.. that's enough for one day. I know it's not very exciting stuff, but believe me, once you tackle this, your understanding of photography and your practice thereof will take a major turn for the better. I'll be back with more on this theory and some tools for you to use for equivalent exposures.

Thanks for reading and please come back!

Mark

Introduction

Hi. My name is Mark Nagel. I am currently studying photography at Brooks Institute in Santa Barbara, CA and loving every minute of it. I have started this blog to try and communicate some fundamentals of photography in an way that is easy to understand for someone of any skill level who would like to develop their photography further. Here are a couple of things that have lead to the writing of this blog.

1. Prior to starting school I found it to be relatively hard to discover internet sources that would help me understand the basic fundamentals of photography that I might then be able to build on with more technical, as well as creative, learning. This is what I want to offer here.

2. Since I've started school, my family and friends, specifically those that are even remotely interested in understanding how to take better photographs, have been not only asking me for advise and expertise that would help them learn (which I am always MORE than happy to give!), but also what resources they can go to online to learn the basics as mentioned above. I didn't know where to send them. And, well guys... this is now your source.

3. As I am back in school and now have a 2 month old, I am very hopeful that this bog will eventually generate even a small amount of income. If it generates enough, combined with my photography for sale on istock, dreamstime, fololia, and alamy (all microstock agencies), and my current job, my wife may just be able to stay home with the kid and not have to go back to work. But we'll just have to see how this thing goes... worth a shot, right??

Thanks for stopping by and please come back soon and often to start learning about photography. And please, PLEASE, especially if you find the information herein useful, tell your friends to stop by and take a look.

Thanks!

Mark