Beginners Guide To Exposure
This article is an attempt to keep you away from complicated numbers and jargon and bring you valuable photography tips to help you feel more confident with your creations and understand a key concept in photography: Light.
In order to capture an image on the digital sensor, it must be exposed to light. In photography, it is important to measure the amount of light that hits the sensor, because too much or too little light can ruin a photograph. You can measure and control light by its brightness (F-Stops) and by its duration (Shutter Speed).
The Triangle of Exposure
There are 3 core elements that make a good exposure: aperture, shutter speed, and ISO.
Let’s use a simple analogy to explain the relationship between the 3 elements of exposure. Think of exposure as the perfect triangle with all the sides and angles being equal. If you change one element of the triangle, it is no longer perfect so you will need to adjust other elements to make it perfect again. Thus, there is a direct relationship between the 3 elements of exposure and once you get the hang of it, you will achieve the desired results in your photographs.
1. The Aperture
Aperture is an adjustable opening in the camera lens through which the light passes to hit the digital sensor. Think of the aperture as window blinds to your room and the wall opposite the blinds is the image sensor. As you open the blinds gradually, you can see that more light comes through and the opposite wall gets brighter and brighter.
Likewise, as you open up the aperture on your lens, more light hits your digital sensor. The size of the aperture is expressed in F stops, which measure and control how much light is passed through the lens. Keep in mind, lower F-Stop numbers indicate more light.
Examples from a typical range of F stops would include: f1.4, f2.0, f2.8, f4, f5.6, f8, f11, f16, f22.
In this scale, the smaller the number (such as f1.4), the larger the aperture is open and the more light passed to the sensor. You may ask why a smaller number means a larger aperture. The reason is the number is actually the denominator of a fraction. Thus, as the bottom number of a fraction gets smaller, the larger the number. So, F 4 would be 1/4 and F 8 would be 1/8 and 1/4 is larger than 1/8.
Every step above represents a 1 Stop change in light intensity. Let’s say that if you have one light bulb and then add another one, the light intensity will increase by 1 Stop. To increase the light by another stop you would need to double the light and so you would have 4 bulbs.
* A smaller F-number, like f/2.0, refers to a wider aperture.
* A high F-number, like f/22, refers to a narrower aperture
A smaller F-number (larger aperture opening) will decreases the Depth of Field, meaning less amount of the image will remain in focus. This is especially good in portrait or macro photography, as it creates a beautiful blur effect.
Now, you may ask what is it with all these different apertures and why should you learn to control the amount of light that gets to your camera sensor or film.
Well, the reason is simple. You get more control. Adjusting the aperture size provides you more creative control on Depth of Field. It allows you to maintain shutter speed at varying light levels, so you can counter camera-shake among other benefits. As you can maintain an ISO level, keeping a consistent graininess to the image.
2. The Shutter Speed
The shutter speed is the next ingredient of a proper exposure. The shutter is like a blinking eyelid. It controls how much light the sensor receives by adjusting how long the Aperture (blinds) stay open for. The slower the shutter speed, the longer the camera’s “blinds” stay open.
The slower the shutter speed, the more light that will hit the sensor. A benefit of this is that shutter speed controls the effort of motion. Whether you want to freeze motion or show motion (e.g. cars in traffic), shutter speed is that element of exposure that will do that for you.
Shutter speeds are measured in seconds and fractions of seconds, such as 5 seconds, 1 second, 1/8, 1/125, 1/1000 of a second. A faster shutter speed can freeze movement (e.g. a surfer). On the other hand, a slow shutter speed, like 5 seconds (long exposure time) allows you to let the movement blur and create amazing art work (e.g. moving carousel), or allow more light in to take low light phtotgraphs.
ISO is essentially the senor’s sensitivity to light. ISO is typically adjusted to allow for low light environments when Shutter Speed and/or Aperture need to remain constant. The disadvantage of using a higher ISO value is that it can increase the noise or grain in your images. So, you want to use the lowest ISO possible and adjust the other two elements of exposure achieve the desired results.
Photographing outdoors on sunny or overcast days you can use ISO 100 or 200, whereas on highly overcast days you may need to increase the ISO up to 400. Also, ISO may need to be increased if you use a smaller aperture and/or faster shutter speed as less light is passing through to the sensor.
Putting it all Together
By now, hopefully you have a better understanding of how these 3 elements depend on each other and why they are so important for your photography. Remember that there is no technically perfect exposure, just the exposure you were trying to create. You may want to play and experiment by adjusting Aperture to create a soft portrait photograph, of using a slow Shutter Speed to create a blurred car driving by. Let your artistic eye guide you and with these powerful photography tips, you will always get good exposure every time.