In the previous article we discussed the three tools that control exposure: lens aperture, shutter speed and ISO sensitivity. This article begins the discussion on putting these three tools to work.
The Exposure Controls
Now that we have our three main characters in place (Aperture, Shutter, ISO) we can begin to put them to work for us. You’ve heard of the “Food Pyramid”? Now meet the “Exposure Triangle”.
Since all three of the controls are linked and equally essential to create the desired exposure, if the value of one point changes one or both of the other two points must change too for the exposure to be maintained.
With three related but separate controls, where do you start?
First, take a slow breath in, and a slow breath out. Repeat as needed.
In general, our goal in photography has always been to use the lowest ISO setting the lighting will allow so that we capture images with little to no grain. ISO 100 produces images with less grain than ISO 400, even in digital.
Armed with the knowledge that we want to use low ISO ratings, that makes ISO the perfect place to start. (Even if after reading this article you choose to stick your camera in good ol’ “P” for Program mode you’ll understand why you at least want some control over the ISO setting.)
The reason we have the ability to change our ISO settings is that we need to be able to adjust the sensitivity of our cameras for all of the different environments we shoot in.
• Outdoors on a sunny day, 100 ISO is perfect.
• Indoors with flash 400 ISO may be better
• At a basketball game where the light is poor and the flash can’t reach to the players we choose 800 ISO or maybe even 1600 ISO.
As photographers we work the ISO scale to our advantage. We choose higher ISO settings in order to capture images in dimly lit settings, yet we are mindful that we don’t want to go any higher up the scale than we need to since we don’t want to capture images that look too grainy. It’s a balancing act, but an easy one with only a little practice.
Because of the special relationship of the three exposure tools, a change to one of them has an effect on all of them. As the ISO sensitivity goes up we require less light to achieve our exposure. The camera can use a faster shutter speed, a smaller aperture – or both.
The first step in exercising control over our exposures is to set the desired ISO. In the examples that follow we can assume that the ISO is the same. To start, we’ve chosen 100 ISO as a base setting. This leaves only shutter speed and aperture controls available to select a good exposure.
The two scales below list apertures and shutter speeds. The apertures get smaller as we move down the list while the shutter speeds get faster as we move up that list.
Lets make the assumption that our camera’s light meter reads f 8 at 1/60 as the correct exposure for the light in our scene. We can accept this setting of f 8 at 1/60 but maybe we are shooting a runner and need a faster shutter speed to prevent motion blur.
If we select a faster 1/125 shutter speed to help stop the action, we need a wider aperture to keep our exposure triangle balanced.
Looking at the chart above we can see that a move to 1/125 shutter matches up to the aperture value of f/5.6. We “lose” one stop of exposure for the faster shutter and “gain” one stop of exposure with the wider aperture so our exposure triangle remains balanced.
As the light changes we need to adapt. The last example was based upon shooting a runner outdoors. But what happens if we move inside to a living room? Since we are using light sensitivity (ISO) as the constant, this means that the initial meter reading in this new environment will change.
Since there is less light in the indoor scene and our ISO sensitivity remained the same, the aperture and shutter scales had to shift against each other in order to achieve an accurate exposure. The meter sets the camera aperture to f/4 in order to use the same 1/60 shutter speed. In this situation it is said that the scene has two stops less light than the outdoor scene.
Though we could shoot our indoor images with this meter reading, there isn’t a lot of room for error. We are operating right at the aperture extreme of our lens. We can change our ISO setting from 100 to 400 and the scales will once again shift against each other in order to maintain exposure.
The change from 100 ISO to 400 ISO is a two-stop change. To maintain the exposure value we can now close down (stop down) the lens aperture value from f/4 to f/8 – also a move of two stops and the exposure remains balanced.
Lets take a moment for review. We have learned that the camera’s meter will measure the light in order to choose settings for the lens aperture and the shutter speed in order to ‘properly’ expose the image sensor. (Proper as defined by the camera manufacturer’s programmers) The camera meter uses the ISO sensitivity setting (aka film speed) as the basis for the exposure reading.
Reactive vs. Proactive Control
To this point we’ve allowed the camera’s meter to measure the light and set the initial aperture and shutter speeds. This means that we have examined what we call a reactive approach to shooting images. The camera is pointed at a subject and the built-in processor reacts to the scene placed before it. Let’s explore why as a creative photographer we might want to take back some of that control and also take a look at the tools that allow us to.
In The Zone
If we set the camera in the “Easy” mode or “Green Zone” we are telling the camera to make all of the decisions for us. We cannot choose ISO, shutter speed or aperture. The camera’s computer will generally select a combination that favors the fastest shutter speed possible with a lower ISO. The camera is programmed to do this to help prevent blurry images from hand-held camera shake and to mitigate image grain.
If your camera has icon modes like Portrait, Sports, Macro or Landscape these modes also prevent the photographer from taking any control of the exposure.
There is nothing wrong with taking pictures in the Easy mode or any of the Icon modes. They perform as advertised and can take a lot of the guess work out of taking a picture. In addition, these modes will give the photographer a very good chance at getting above average pictures. And the photographer doesn’t have to spend any time at all making settings on the camera. But what if sometimes we want more than “above average” pictures?
Yep, you have to seize your camera. Grab a hold of it and turn a dial, and do it with a little understanding. Photography is truly a pursuit where a little knowledge goes a very long way.
A good first step is to set the camera in the “P” for Program mode. Program is very much like the “Easy” mode in that the camera will suggest an exposure for the image about to be captured. The big difference between Green Zone and the “P” mode is that the photographer can choose to override the camera’s settings. Plus the photographer can set ISO sensitivity.
In Program mode the photographer can first see the camera’s suggested starting exposure and then using a Program Shift wheel to move up and down the table of shutter / aperture pairings until a preferred setting is found.
Sounds easy, but why would a photographer want to take that control?
We have established that shutter speed settings and apertures pair up in specific ways at different light levels in order to give us an acceptable exposure and capture our image. However shutter and aperture controls have an even greater effect on our images. In the final article on Exposure we will take a look at shutter and aperture effects and answer the question “Why?”