Exposure is a term you will hear a lot in photography. It is used to describe the amount of light traveling through the lens and camera body, eventually collected onto the film or image sensor. Correct exposure is obtained through a delicate balance between shutter speed, aperture, and the sensitivity of the film or image sensor (this is generally referred to as ISO).
There is a correct exposure (objectively speaking) for every scene. For the purpose of this hub, we will focus on the techniques to obtain proper exposure.
Though there are quite a few things to consider when it comes to exposure, the most important thing to grasp is that good exposures require a general understanding of how to measure light. It also requires a lot of practice. It's important to master exposure so you can spend your energy being creative instead of wondering if the image will be too dark or too light. One of the best ways to accomplish this is to shoot in manual mode so that you are in control of this important part of making images. Digital cameras help this learning process by providing instant feedback on your shot via the LCD display. You'll therefore know immediately if your shot is underexposed or overexposed, allowing you to adjust accordingly when needed.
Shutter Speed
Let's discuss the concept of shutter speed in greater detail, as it is a key factor in determining the correct exposure for a scene. The shutter is an opening in the camera that allows light to pass to the film or image sensor. How much light it lets in is not based on size, but rather the amount of time it is open. A shutter speed can be fast, like 1/1000th of a second, or it might be slow, like 1/4th of a second.
A fast shutter speed will stop action, while a slower speed will render moving objects as blurred.
It is important to note (this will be repeated several times) that proper exposure is a relationship between shutter speed (time), aperture (amount of light), and ISO (sensitivity of the film or image sensor).
Aperture
The aperture is the opening of the lens. It controls how much light passes through the lens elements, based on how big or small the opening is. An adjustable bladed-metal iris enables the photographer to control the size of the opening, which is measured in f-stops (such as f/5.6, f/8, or f/16). Higher f-stop settings translate into smaller aperture openings; lower f-stop settings yield wider apertures. This can be confusing as it is counterintuitive (one would expect a higher number to correspond to a bigger opening); however, if you consider that this measure is actually a fractional relationship, then it is easier to remember. For example, you'd likely rather have 1/5th of your favorite pizza or pie (for example) than a mere 1/16th.
Equivalent Exposure
One of the most important aspects to understanding exposure is this relationship of shutter speeds and apertures. This is also referred to as reciprocity. The most important reason to understand the concept of equivalent exposures/reciprocity is so that, in any given situation, you can prioritize creative choices at a moment's notice, based on what is happening in front of you when you have your camera to your eye.
Shutter speed and aperture work together to create a proper exposure. You can explore many different combinations of aperture (which controls the amount of light that passes through the lens) and shutter speed (which controls the amount of time light is exposed to the image sensor). This allows you to shoot several images of the same subject, which will have different qualities of depth of field (what's in focus from front to back); yet, they all have equal amounts of exposure.
The chart below shows equivalent exposures based on an aperture of f/5.6 and a shutter speed of 1/125. As you can see, when you move up or down an f-stop, you need to halve or double the shutter speed, respectively.
Aperture Shutter (in seconds) Most Light f 2 1/1000 Least Light............ f 2.8 1/500........................ f 4 1/250........................ f 5.6 1/125........................ f 8 1/60........................ f 11 1/30........................ f 16 1/15........................ f 22 1/8........................ f 32 1/4........................ f 45 1/2............ Least Light f 64 1 Most Light
If you understand this most basic concept, many things will fall into place to help you get correct exposures. This is especially true if you take the time to memorize full stops of exposure. All of the settings above are full-stop measures of exposure. Think of them as inch-marks on a ruler, or full values. Many of you are shooting with cameras that also have 1/3 or 1/2 stops. If you have two shutter-speed settings between 15 and 30, for example, you know you have 1/3-stop increments; if you only have one, then you have 1/2-stop increments.
ISO (Sensitivity)
The other factor beyond shutter speeds and apertures that will affect the overall exposure is ISO (which is a measure of the sensitivity of film or images sensor).
ISO, or sensitivity, is a measure of how fast the film or image sensor reacts to light. A higher sensitivity means that the camera needs less light to make an exposure. This allows an exposure to be made with either a faster shutter speed or a smaller aperture. The specific film type or ISO setting you choose determines this sensitivity. If you've shot film before, then you are probably already familiar with this as the ISO ratings of film, such as 100, 200, or 400. Films for extremely low-light photography are available in ISO speeds as high as 1600 and 3200.
The higher the ISO rating, the more sensitive to light the film is. And with a digital camera, the higher you set the ISO, the less light will be needed. When using a higher ISO, for example, it is more likely you will be able to hand-hold a shot in lower light -- without the shutter speed dropping so low that camera shake will yield a slightly blurred image. If you are using a lower ISO, you will need much greater light levels, or a tripod, to ensure a steady shot that is sharp.
Left Field Photography
Angel Whisenant is a photographer based out of Virginia Beach, Virginia. She has been photographing people for 10 years. Book one portrait session at half-off in the month of July, your friends session is free. Virginia Beach portrait photographer
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