How to check whether your exposure is correct?
In this weeks article, we are going to talk about how to check whether your exposure is correct, and how to get the perfect exposure settings for each image. To correctly expose is often regarded as a difficult matter. Especially for beginners, it can be hard to grasp. After failing a couple of times, beginning photographers might resolve to the automatic mode of their camera again. With this article, I will try to show that it doesn’t have to be that difficult. With learning how to read the histogram you will see that it is a very good tool to find the best exposure and to manipulate and correct the exposure to get the image you want.
In photography, the basic element is light. You won’t get a good picture without a proper exposure; it’s as simple as that. That used to be the case with analog cameras and it is no different in the digital era. If there is too little light on the sensor, the photo is underexposed. If there is too much light on the sensor, the picture will be overexposed. In the case of an underexposed photo, the details will disappear in the dark areas and, in an overexposed photograph, in the light areas. The room to correct this afterwards is very limited so it is best to get it right in camera. In contrast to the analogue era, however, we now have some amazing tools that we can use to guide us in finding the best exposure we need to get the results we desire.
Required shutter speed
The required shutter speed for a well-exposed photo is determined by the amount of light and the subject (still or moving), in combination with the aperture and the ISO value, plus the intended effect of the photo. If you want a waterfall to be sharp and detailed, you use a shorter shutter speed than when you want to emphasize the effect of moving water. The ‘correct’ exposure therefore depends on what you want to show. A good example of a ‘correctly’ exposed image is Image 2.
Because the northern lights were moving constantly, I did not want to make the shutterspeed too long because that would mean the beautiful details in the aurora would be lost. Still, I did not want to lose too much light because then the photo would become too dark. By choosing a shutter speed of 5 seconds and setting the aperture and ISO accordingly, I succeeded in freezing the movement of the northern lights without losing detail in the foreground.
Back in the days
Back in the days of the analog camera, it was necessary to determine the correct exposure values using an external light meter. This was based on knowledge, experience and a certain dose of luck. This was really hard practice and you had to get a lot of experience to master this. Film was expensive so you wanted to have it correct right away. There was no way to preview your image. Fortunately, nowadays the camera has a number of very useful functions. We have the LCD-display, the built-in light meter, and the histogram. I deliberately put them in this order, because that is the way they should be used, as we will learn in the following part of this article.
Now you might think that the image on your LCD screen or digital viewfinder provides sufficient information about the exposure. Overall this might be true, but it is anything but accurate. Because you can set the brightness of the LCD screen, it is variable. Furthermore, environmental factors such as sunlight, reflections or darkness also influence what you see on the screen. It is a handy check to know if you’re getting there, but it’s not a reliable method to perfect your exposure. Therefore, the LCD-display should only be used as a rough indicator.
Built-in exposure meter
To determine whether your settings are correct or not, you can use the built-in exposure meter. You do this by pressing the shutter button halfway down (as with autofocus). A bar with scale will now appear. This is the exposure indicator. The pointer indicates whether your exposure is correct (image 3). The camera thinks the picture is right when the pointer is in the middle. With an underexposed photo, the pointer is on the left. With an overexposed photo, on the right. The numbers are called stops. From 0 to -1 means half the amount of light, and 0 to 1 means a double the amount of light.
Personally, I often use the outcome of the light meter as an indication. It often happens that my exposure turns out to be either above or below zero. This really depends on my subject and my intentions. For instance, photographing in snow or straight into the sun messes with the exposure meter. In those situations you need something else, something much more reliable. Luckily we have it! It is called the histogram!
The histogram is an amazing tool! Unfortunately, it is also feared by a lot of people because of its seemingly complex appearance. For that reason, a lot of (beginning) photographers won’t use the it. This is a pity because it offers so much information and once you know what it means, it is really simple to use. As mentioned, the histogram is a much more reliable method to check whether your exposure is correct and to make sure you get the result you want.
Let me begin by explaining what a histogram is by using a definition: the histogram is a compressed bar graph of a frequency distribution. This might sound a bit abstract but stay with me, it will be a lot easier once you know what the graph stands for. It is a graphical representation of an exposed image, which shows you how many pixels in your photo have a certain tone on a scale from 0 to 255. The horizontal axis runs from pure black (0, very dark) to pure white (255, very light), with mid-gray in the middle.
Each tone is one pixel wide. The vertical axis shows the amount of pixels that have that certain tone. If you see a peak, then many pixels have that tone. When the photo is predominantly dark, then the weight of the graph is on the left. With a light photo, the weight is on the right (Image 4 & 5).
How to read and use the histogram
Using the histogram, it will become quite easy to see when details will be lost in either shadows (pure black) and/or highlights (pure white). A peak at the immediate left side means that image information disappears in pure black. A peak against the right side means information dissolves in pure white. Both are not desirable, but if you are forced to choose (because of extreme contrast difference for instance), go for a peak on the pure black side.
In general, black shadows are experienced as less disturbing than blown out highlights. The shape of the graph depends on the subject and the amount different tones (light and dark areas). And, because all brightness information is displayed in this graph, we can use the histogram for checking our exposure because it accurately reflects the brightness levels. Moreover, you can clearly see what you are doing using live view and therefore prevent errors when fine-tuning your exposure (Image 6).
Because each picture is different, your histogram will be different too. If the histogram shape doesn’t match the typical mountain shape with the center of gravity in the middle, it does not mean that it is poorly exposed. Do not compare your photos with a certain type of histogram. It is a tool that is useful for correcting over- or underexposure and to check whether all tones are represented or not. It is not a fixed rule that you should keep with every shot. The final exposure is determined by what you want to transfer with the photo and your creative vision. This means that you sometimes deliberately overexpose a photo and another time you will underexpose. Sometimes, you even have to over- or underexpose to get the correctly exposed image.
Correctly exposing light scenes
In situations where you have predominantly light areas in your photo, such as a beach or in the snow, the automatic mode will produce an underexposed photograph. To illustrate this, I used a picture of the Paard van Marken lighthouse in the Netherlands (Image 7). At the end of the winter, there was a beautiful ice deposit due to prolonged cold and strong eastern wind. I wanted to capture this during blue hour (an hour before sunrise) to emphasize the icy cold even more.
The first photo is exposed to the middle. The gravity point is exactly on medium gray. It can clearly be seen that the photo is underexposed. As a matter of fact, the pars that should be white turned out medium gray. In order to get the correct exposure, I’ve exposed this image towards the right, which means that the center of gravity within my histogram has shifted to the right side of the graph.
Put it to use!
Almost all modern cameras have a means to view the histogram. Depending on the brand and type of camera, this can be live, which is awesome because it immediately shows the effect of adjusting the shutter speed, aperture and/or ISO. Your camera doesn’t have a live view of the histogram? That’s no problem; use the light meter of your camera as an indication, take a picture and view the histogram in the viewer. Adjust the exposure and repeat until you are satisfied.
Thanks a lot for reading
That’s it for this week’s article! Thanks a lot for reading! I hope you’ve enjoyed it and you learned that using the histogram isn’t scary at all. I hope it will help you to get better images. If you have any questions, please let me know! If you enjoyed this article please feel free to share on social media! And, if you like my photography, please follow me on Instagram @harmenpiekema
I would like to thank my buddy Cody Fjeldsted for proofreading this article! Your help is awesome and means a lot, thank you so much.