We’ve all been there.
We upload our photos into our computer only to realize that the photos are either underexposed or overexposed. Now your only option is to fix it in post, which as you may already know, isn’t always the best option. It’s always best to correct the exposure in your camera first so you’re not dealing with it all in the editing software.
In photography, your exposure determines what gets recorded on your camera’s image sensor. The science behind exposure in photography is called Sensitometry. There are three things that control your exposure: ISO, aperture and shutter speed.
This article will teach you the basics of these three settings, as well as different techniques you can use to measure the exposure. With this knowledge in mind, you’ll be able to expose your photos perfectly every time!
First, let’s look at ISO. ISO speed is a value that represents how sensitive the sensor in your camera is to the light passing through the lens and hitting the sensor. Each value of the ISO rating represents what is known as a “stop” of light. Each ISO number represents a doubling (going up) or a halving (going down) of the sensor’s sensitivity to light.
The ISO can easily be changed in your camera in the menu settings or on a dial. Keep in mind that the higher the ISO setting, the more grainy your photos will appear. Depending on your lighting situation, you’ll want to adjust the ISO accordingly.
The aperture in your camera’s lens controls the volume of light that passes through the lens to hit the sensor. Aperture settings are measured in numbers, called f-numbers, or f-stops. Each f-number represents a stop of light.
An easy way to think of aperture is to compare it to the pupils in your eyes. The bigger the opening, the more light wil come through just like how your pupils function. It expands to allow more light in darker settings.
Your shutter speed is the speed at which your camera shutter (sometimes called the curtain) opens and closes. This duration determines how much light passes through the lens to reach the camera sensor. Shutter speeds are measured in seconds and fractions of seconds. Each shutter speed value also represents a “stop” of light.
If you’re hand-holding your camera, remember to set your shutter speed to at least 1/60th sec. Anything slower than that will cause your images to be blurry.
Check out the camera settings in the photo above. The display shows you various camera settings that let you control the exposure. As you can see, the ISO is 200, the aperture is F7.1 and the shutter speed is 1/200 (one two-hundredth of a second).
The key thing to remember about these three camera settings is that they are interdependent. They depend on each other. This means that, if you change one setting, you must change one or both of the other settings in order to maintain your correct exposure.
For example, if you increase your aperture f-stop from F7.1 to F5.6, you make your aperture larger, which increases the amount of light passing through the lens and hitting your camera’s image sensor. Increasing the size of your aperture affects your depth of field by making it shallower.
If you reduce your shutter speed, you change how movement is captured in your image. Fast shutter speeds capture fast movements. Slow shutter speeds do not capture movement, but instead render movement as a blur. Longer shutter speeds have the advantage of letting more light hit the sensor, something that is often necessary during night photography.
Then there’s your ISO. If you decrease your ISO, your images will be sharper but you will require a wider aperture or a slower shutter speed to balance out the exposure.
ISO, Aperture and Shutter Speed are Interdependent
Again, the key thing to remember about these three settings is that they are interdependent. Change one, and you change your exposure. If you have a perfect exposure, for example, and you increase the size of your aperture, you suddenly make your image overexposed. You will need to increase your shutter speed or lower your ISO to compensate for that wider aperture.
Increasing the ISO allows for shooting in lower light situations, but you increase the amount of digital noise (also called grain) in the image. It is impossible to change one element and not obtain an opposite effect in how the other elements affect the image. Check out the image below. This is the result of a high ISO setting, causing image grain. The photo lacks clarity and sharpness.
Underexposure, Overexposure and Correct Exposure
To say an image is underexposed means the image does not contain enough details in the shadows or dark parts of the image. Of course, it also simply means your photo looks too dark.
Overexposure means the details in the brighter or whiter parts of the image are missing. These areas are known as the highlights. They are, as is said in the trade, “blown out” in an overexposed image.
Correct exposure means the image has the correct balance of details in the shadows and details in the highlights. Again, let’s makes sense of this with examples!
First, look at the correctly exposed image above. Notice that you can see details in both the shadows and highlights. From the floor, people, to the countertops and walls, everything is sharp and properly lit. This is well-exposed shot with a good balance of highlights, shadows, and contrast.
Now look at the underexposed image above. In this instance, this photo is slightly underexposed so it gives off a moody tone. This is most likely intentional and can be a great way to get more creative with your photography. However, a completely underexposed image will lose all detail and clarity. Luckily, there are several ways you can fix an underexposed image either in the camera or in post editing which we will go over later in this article.
The photo above is quite overexposed. Notice how the details are lost because the highlights are so blown out. You can barely see the texture of the cheetah’s fur as it’s blending in with the snowy background. It is harder to fix an overexposed image compared to an underexposed image, so do your best to correct an overexposed photo while you’re out shooting! As we mentioned earlier, play with the ISO, shutter speed and aperture to get the perfect exposure.
Get your exposure right with the exposure scale
On the LCD display of most DSLR cameras there is an exposure meter that indicates if your image is going to be underexposed, over exposed, or just right.
At the left end of the meter you see a + sign. At the right end of the meter you see a – sign. And in the middle of the meter, you see a 0 and a vertical bar beneath. As you adjust your ISO, aperture and shutter speed, this vertical bar travels to the left or to the right to indicate that you are either overexposing your image (the bar is to the left of the 0) or underexposing your image (the bar is to the right of the 0).
To adjust your exposure, change your ISO, aperture or shutter speed until the vertical bar is centred on the meter scale, under the 0.
Get the Exposure Right with your Histogram
The other way to tell if your image is correctly exposed is to take a picture and then to examine the histogram for that image. Most of today’s DSLR cameras have at least one histogram that shows the overall brightness of a scene.
The histogram is the rectangular box with the vertical lines in it that form an image that looks like a wave. This shape tells you if your image is underexposed, overexposed or correctly exposed. If the wave is bunched up at the left side of the histogram, your image is underexposed. If the shape is bunched up at the right end, your image is overexposed. And if the shape is divided evenly between the left and right ends of the histogram, your image is correctly exposed.
The big advantage of DSLR cameras is that you can experiment until you master exposure. Even if you make a mistake, digital files can be very forgiving and allow you to correct the exposure even after you take the shot. This gives DSLR users endless freedom to play around with varying levels of exposure. Play around with your ISO, aperture and shutter speeds enough, and you will eventually capture the perfect exposure every time.