How Calculating Exposure Gets You The Perfect Image Every Time!

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How Calculating Exposure Gets You the Perfect Image Every Time!

Do you ever wonder why your images are not quite as impressive as you’d like them to be? You may need to re-think calculating exposure when you’re shooting. If you have your camera set to auto, then there’s your first obstacle. Learning how to shoot in manual is your first step toward improving your images.

Auto? Manual? What?

What is the difference between auto and manual? Great question! The auto setting on your camera will assess the current lighting situation you are in and make automated decisions to give you what it deems the “best exposure.” Putting your camera in the manual setting allows you to be in charge of those decisions and choose what settings work best for you to get your desired result. Shooting in manual mode will slow down your process and cause you to think differently. It will also allow you to make a more intentional effort at composition and lighting and how you’d like your image to look. Shooting in manual mode is not hard, but it does take some practice. And remember, no risk, no reward. You can do it!

Calculating Exposure

When photographing just about anything, it’s critical to know how to calculate exposure correctly. You can look up an exposure calculator but honestly, it will not do much to help you understand exposure value unless you understand the basics of the exposure triangle. Understanding how to calculate exposure begins when you understand how the aperture and shutter speed work together. You also need to understand how your camera’s sensor handles light and the relationship between the sensor’s light sensitivity, aperture, and shutter speed.

The exposure Triangle

Let’s take a quick look at the three elements of the exposure triangle, aperture, shutter speed, and ISO.

Aperture (f/stops)

Aperture is the opening in the center of the lens through which light passes. An F stop indicates the amount of light that passes through an aperture. The more you open the lens (lower f/stop #), the more light passes through the aperture. Opening your lens one full f/stop doubles the amount of light entering the camera. F/2 brings in twice the light of F/4. The lens you’re using determines the range of aperture.

Shutter Speed

The shutter, located inside the camera body, is a mechanical device that controls the length and rate of time that light is allowed to contact the sensor. The longer you leave your shutter open, the longer the light is touching the sensor.

ISO

ISO stands for International Standards Organization and measures the level of sensitivity your camera has to the light that enters through the shutter. The lower the ISO number, the more sensitive your sensor will be to the incoming light. So bright sunlight means you will be using ISO 100, which is the lowest.

Putting the Exposure Triangle to work

You will achieve the correct manual exposure when you use aperture, shutter, and ISO together in sync. When you set your camera on AUTO mode, the computer brains inside the camera decide what settings are best for the environment in which you’re shooting based on the light. When you switch your camera to MANUAL mode, you get to decide your settings. I don’t know about you, but I love to be in control! In photography, taking control of your settings sets you up for much greater success in calculating your exposure and getting the result you want.


If shooting in manual is new to you, check out The Ultimate Guide to Shooting in Manual. There I break down the exposure triangle in greater detail and show you the basics for how to get started. Go ahead and check it out. I’ll be here when you return!

The Perfect Manual Exposure

Getting the perfect exposure isn’t easy, but there are a couple of essential tools that will make it easier. Learning about your on-camera meter and the histogram are significant first steps. Get into the habit of referencing your meter and your histogram and changing your settings on the fly. This habit will allow you to become much more intuitive when you’re on location. The best way to learn and form a healthy habit is to practice! Let’s begin by talking about the in-camera meter.

The Light Meter Simplified

Inside your camera is a built-in light meter. This meter works by reading and analyzing the light that is currently coming into your camera. The meter takes that information, adds it to the current camera settings, and gives you feedback on the exposure. When you look inside the viewfinder, you will see a meter reading that looks like this:

Graphic of an in-camera exposure meter
the in-camera exposure meter

The idea is to get that small line on the bottom lined up directly at zero, as shown in the image. The line will move to the left or right as you change your settings or change what you’re pointing the camera at. If the line is to the left, your image will be under-exposed or too bright. If the line is to the right, your image will be over-exposed or too dark. As you make adjustments to your settings, you’ll see the line move from left to right and back.


When you are out in the field shooting, you will need to make fast adjustments to your aperture, shutter speed, and ISO to get your exposure just right before clicking the shutter. Get familiar with your camera and how to make adjustments to these three settings. Then practice! Are you sensing a theme? Practice does indeed make progress!

Perfection is subjective in calculating exposure

Each camera has a teeny bit of variance between the settings and what you want to see with your eye. For example, when my camera thinks my image is perfectly exposed, I usually find it’s a bit dark for my taste, so I like to adjust my meter to accommodate that. If I’m taking photos of a landscape, I usually take a few images with several different exposures, which serves two purposes. First, I can choose the one I like best when I’m back at my laptop processing my images in Lightroom, and second, if I choose, I can use those images together to create one amazing HDR image.

Your Meter and How to Use It

When you are using your meter to determine manual exposure, place the camera’s focus point on the main subject of your image. This placement will give you the most accurate exposure feedback. Let’s say you are photographing a happy couple with a dark wooded area in the background. Look through the viewfinder and place the little focus square on your subjects’ faces. The meter will tell you how you can adjust your settings to the correct exposure for their faces. If you are looking at your meter and adjusting settings while the focus square is on the dark woods, your resulting image will have correctly exposed trees behind them, likely leaving them too bright and washed out.

A Practical exercise

Try this: Take your camera and look through the viewfinder wherever you are. Move it around, keeping an eye on the meter. Try to find bright and dark areas in your environment and watch how the meter changes as you move your camera around. Now when you decide what you want to focus on – say, your dog is laying in a sunbeam, you’ll know how you need to adjust for exposure. Make sure you’re reading the meter when it’s pointed right at puppy’s face (not the background) and then changing your settings accordingly. Perhaps you will want to make a quick bump in ISO if you aren’t worried about grain. Or maybe you can adjust shutter speed if you’re not concerned with motion blur. Or there’s always a quick adjustment to your aperture if that doesn’t affect your depth of field.

Another Example

Let’s talk about a scenario that can be a bit tricky. Imagine you are at the beach photographing a couple in front of a gorgeous sunset. If you meter for your subjects’ faces, you may get a washed-out sunset behind them. If you meter for the sunset by placing that focus square on the background, you will get a beautiful sunset, but your subjects will be so dark you may not be able to make out the details of their faces. What’s the solution here?
The solution is simple. Expose for somewhere in between, leaning a little more toward the settings of their faces. After all, if you want the people to be the main focal point of the image, you want to see their faces. If they are a touch dark, you can brighten them up while editing in Lightroom. You can also make some adjustments to the sunset for the perfect color, perhaps bringing down the highlights and bumping up the vibrance.

Now let’s talk about the Histogram

Now that you’ve committed to practicing and have a basic understanding of how your in-camera meter works let’s talk about the histogram. Learning to read the histogram is equally as important as understanding metering when learning about the perfect exposure.

The histogram

What the heck is a histogram anyway? The histogram is a little graph/bar chart filled with big information. It indicates the brightness levels in an image from darkest darks on the left side to brightest brights on the right. The histogram is a fantastic tool and can show you at a glance if your exposure is on target.


You can see a histogram on the LCD screen on the back of your camera. You can peek at it immediately after taking a photograph and make adjustments to your exposure. Also, the camera records this information with the image file, so you will be able to see the histogram when you’re editing later.

What’s a Perfect Histogram?

Let me make something very clear here. I can assure you that there is no “perfect” histogram. You may hear somewhere that a histogram needs to look like a mountain or a valley or a series of peaks. But trust me when I tell you – those could all be perfect histograms and bummer histograms. The histogram will change with the conditions you’re shooting and is merely a tool to help you better understand how you expose your image.


So what do I look for if there’s no such thing as a perfect histogram? You are looking for information that tells you if your image is over or underexposed. From this example of my husband sitting on the lawn tractor with my grandson, you can see that this is a properly exposed image SOOC. Why? Because there are darks and lights all well-represented throughout the histogram.

calculating exposure helps create a well-balanced image like this one with a grandpa on a tractor

Here is what the same image would have looked like overexposed. See how the histogram shows peaks on the right side? Those peaks show that most of the image consists of light tones, which is not accurate to what you’re seeing.

calculating exposure helps avoid overexposed images like this one with a grandpa on a tractor

And now, let’s look at the same image underexposed. See how the histogram shows peaks on the left side? Those peaks show that most of the image consists of dark tones.

calculating exposure helps avoid dark images like this one with a grandpa on a tractor

A Word About Clipping

The first thing I look for is clipping. Clipping is when you over-exposed or under-exposed portions of your image to the point where you lose detail. Here’s an example from a session of my naked cat, Scarlett No’Hara, taken in my home studio.

Calculating exposure helps avoid clipping as shown in this image of a cat with a bright white light in the upper left corner of the image

See the histogram in the upper right? Can you see how the peaks are all squooshed over to the left? That means most of this image consists of dark tones. That white triangle in the upper left is my softbox light. Watch what happens when I click on the clipping icon in Lightroom. The clipping icons are the small triangles in the upper corners of the histogram.

Calculating exposure helps avoid clipping as shown in this image of a cat with a bright white light shown in red in the upper left corner of the image

Once I ask to see clipping, the white light turns bright red because that light is so bright that I’ve lost all detail in it (clipping). I’m okay with that in this example because I will crop that portion of the photo out anyway. I may have not calculated exposure very well for the softbox, but I am more concerned with Scarlett’s details and her expression. She has no clipping on her face, so I’m good. I wanted a dark and moody image, and I got it. If I were trying to show that portion of the image, I would need to go back and adjust my exposure so that I do not see clipping.

Clipping Can be Subtle

Here’s another example:

Calculating exposure helps avoid clipping as shown in this image of a dog lounging in the sun

See how there are red dots all over the carpet in the foreground? Those dots indicate areas where the image is overexposed. I made a few adjustments in Lightroom when post-processing, including the exposure and the color balance. I could have made a couple of exposure adjustments right in the camera when I shot this image had I used the information from the histogram on the back of the camera. In this case, it wasn’t a significant problem, but moving forward, I learned a valuable lesson. I may be able to get another portrait of my dog in the sunbeam, but when it counts on a once-in-a-lifetime vacation, I will know how to get the correct exposure using the histogram’s feedback.

Calculating Exposure

Putting it all together!

Spend some time studying the exposure triangle, reading your in-camera meter, and reviewing the histograms from images that you’ve done right and images that you would improve. You will soon begin to see all the connective tissues that will help you to calculate exposure when you’re shooting. The good news is this: Today’s technology allows us to correct most oopsies when post-processing. However, the closer you can get to a picture-perfect image straight out of the camera, the less time you’ll have to spend fixing mistakes and the happier you will be with your results!

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