Category: Photography

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Understanding Dynamic Range

Last week, I wrote an article about exposure bracketing. In the article I mentioned that exposure bracketing can increase the dynamic range of your camera. Looking back, I probably should have written this article explaining what dynamic range is before writing an article on how to increase your camera’s dynamic range.

What is Dynamic Range?

Have you ever snapped a photo and the photograph didn’t capture the scene like you wanted? Maybe the colors weren’t quite right, the shadows were too dark, or the highlights were too bright? Maybe the foreground was perfect, but the sky was blown out? The reason for this disconnect between what you see and what your camera captures is dynamic range.

Dynamic range is the ratio between the largest and smallest values possible; in the case of photography, we are talking about the ratio between the lightest and darkest parts of an image. The human eye has a larger dynamic range than a camera. The best cameras can only capture about half of the range of luminosity as the human eye. This is why you can see a person’s face clearly when they have light behind them, but a camera will only capture the brightness of the light, leaving their face in shadow.

Overcoming Dynamic Range Limitations

As mentioned last week, one way to overcome the shortcomings of your camera’s dynamic range is to use exposure bracketing. With exposure bracketing, you can take several photos of the same scene with different exposure levels. The different exposures can then be combined in photo-editing software to bring details of both the shadows and highlights into the final image, resulting in an HDR, or high-dynamic-range, image.

Another method to overcome dynamic range limitations is to use a graduated neutral density filter when taking the capture. Neutral density filters darken the image to allow for longer exposures. Graduated filters are dark on one side and gradually lighten toward the opposite side. The darker side of the filter is placed over a high-intensity region, like the sky, and the light side is placed over the darker areas, like the foreground. This helps to even out the luminosity across the entire scene. Graduated neutral density filters don’t provide the same amount of correction as exposure bracketing, but they’re useful for shots where the difference between light and dark isn’t as drastic.

Is It Worth It?

You may be asking, “Is all of this worth it?” The answer to that is both simple and complicated: “It depends.” As with anything in life, there comes a point where the amount of effort exceeds the value of the rewards. No matter how much you increase the dynamic range of an image in editing, you will still be limited by the method of displaying the photo. Most computer screens don’t have the same dynamic range as the human eye, and most printers can’t print in the same dynamic range as your computer screen. If you’re planning to print your photograph, an HDR image may not yield the results you see on screen, but it will be better than an image with no correction at all.

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Exposure Bracketing

As a photographer, it can sometimes be difficult to get the correct exposure across your entire scene. I find this especially applies when taking landscape photographs with a bright sky and when taking photographs at night. This is when a technique known as exposure bracketing can be extremely useful. Exposure bracketing can increase the dynamic range of your camera so you don’t lose some of those details that inspired you to take the photograph in the first place.

So what is exposure bracketing? Simply put, it’s when you take a series of photos at different exposure levels, which you can then blend together to increase the dynamic range of the final image. It’s also sometimes known as HDR or exposure blending. Take these three photos for example:

Exposure bracketing example

In the first photo, the details in the building can be clearly seen, while everything else in the shot is extremely dark. In the second photo, the building is slightly blown out and most of the scene is still too dark, but some of the side details are starting to show up. In the third photo, the building is extremely blown out, but the details in the lawn and the underside of the trees are nice and clear. By combining these multiple exposures in Photoshop, I was able to create an image I was really happy with:

"Mount Timpanogos Temple at Night" (2017) by K. Bradley Washburn

Most digital cameras have a built-in function for exposure bracketing. The built-in function will take a series of 3-5 photos, depending on your camera. If more exposures are needed or desired, you can take a set of photos using exposure bracketing, adjust the base exposure, then take another set of photos. The above image was actually created using ten differently exposed photos, layered on top of each other in Photoshop.

Even if your camera doesn’t have a built-in function, you can still use exposure bracketing. Simply set up your camera and manually adjust the exposure between each shot.

Each camera manufacturer treats exposure bracketing differently, so I can’t go into detail on how to use it on your camera. You should consult the user manual for specifics concerning your camera.

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Understanding Exposure

When you shoot a photograph, what you’re really doing is taking the light you see and capturing it on film or in a digital file. In fact, the word ‘Photography’ is a combination of two Greek words which literally mean “light drawing”. To create a good “light drawing” it’s important to understand how cameras control the amount of light captured. This is called exposure, and it refers to the amount of light passing through the camera lens and reaching the camera sensor.

The Exposure Triangle

Exposure can be best understood using what is often referred to as the exposure triangle. The exposure triangle is the way a camera maintains the correct exposure for an image, and is composed of three elements: aperture, shutter speed, and ISO. In the exposure triangle, these three elements are related to each other, and if one of them changes at least one other must change to maintain the correct exposure.

The Exposure Triangle
The Exposure Triangle.
Image courtesy WClarke and Samsara, CC BY-SA 4.0, via Wikimedia Commons

Aperture

Aperture refers to the diameter of the hole in the lens that lets the light in. The larger the diameter of the hole, the more light can reach the film or the camera sensor.

Aperture diameter is measured in f-stops. An F-stop refers to the ratio of the focal length of the lens to the diameter of the aperture. The important thing to remember is that the smaller the f-stop number, the larger the diameter of the aperture.

Mechanically, the aperture is part of the lens, not the camera body. When you hear someone speak of a “fast lens” they are talking about a lens with a large maximum aperture, such as f/1.8.

Shutter Speed

Shutter speed refers to the length of time the camera’s shutter is held open, allowing light to hit the film or camera sensor. Shutter speed is measured in fractions of a second. You will often see shutter speeds written as 1/250 or 1/125. For a shutter speed of 1/250, the camera’s shutter is held open for one two-hundred-and-fiftieth of a second.

In low light settings, longer shutter speeds are often used to get a correct exposure. On most modern cameras, the longest automatic shutter speed available is typically 30 seconds.

ISO

For beginning photographers, ISO can be the most confusing part of the exposure triangle, or at least it was for me when I started out. In film photography, ISO is also referred to as film speed. This refers to how sensitive the film is to light.

In digital photography, ISO can be thought of as how sensitive the camera sensor is to light. This is not technically correct, as ISO is really an algorithm run by the camera software, but it helps to think of it this way.

With ISO, the larger the number, the more sensitive the film or camera sensor is to light. Higher ISO numbers allow the camera sensor to capture more light, but higher ISO numbers also introduce more noise into an image. For this reason, it’s usually recommended to shoot using the lowest ISO number you can get away with.

Choosing the Correct Exposure

Unless you are using Manual mode, your camera will adjust at least one of these settings for you. Cameras have a lot of different modes which are beyond the scope of this article, but a good setting for beginners is “aperture priority” mode. This is usually shown as an A or Av on your camera’s dial.

Aperture priority mode allows a user to set the aperture and ISO values, and the camera will choose the correct shutter speed to maintain a proper exposure. If you find the shutter speed is too slow, you will need to adjust either the aperture or ISO to compensate.

I’ve mentioned correct exposure several times in this article, but it’s also important to note that proper exposure is as much a choice of the photographer as it is a technical aspect of photography. Sometimes photographers, including myself, will intentionally over- or under-expose an image during capture. The original exposure can then be adjusted later in post-processing or maintained as an artistic choice. Whatever exposure choices you make, remember to always have fun and don’t be afraid to experiment.

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The Quest for the Perfect Shot

When capturing a photograph, what makes the perfect shot? Is it the lighting? The subject? The background? A combination of all three?

Maybe it’s the camera. Is a DSLR or mirrorless camera better than a cell phone? Is film better than digital? What defines better?

As a landscape photographer, my idea of the perfect shot may not be the same as if I were a portrait photographer. What may be the perfect shot for one landscape photographer may not be the perfect shot for another landscape photographer. Photographers are artists, and art is subjective.

A couple of years ago, I visited the Getty museum in Los Angeles. There were many great exhibits, but one particular piece caught my eye. The piece was a group of 17 silver gelatin prints, photographed by Robert Kinmont, and titled My Favorite Dirt Roads. The photographs themselves were not anything special, experts would even call them amateurish (this was intentional, by the way), but they made me feel something.

To me, that’s what makes the perfect shot. That connection, that feeling. It doesn’t have to be technically perfect. It doesn’t have to be large enough to hang above your living room couch. It just has to resonate with you on a level that makes you remember it years later. You may not even remember what the image looks like, but it makes an impression on you that lasts. Sometimes, we can’t even define why a particular image makes us feel something.

With My Favorite Dirt Roads, the connection was clear. I grew up in a small town in the middle of nowhere, and the piece made me remember my own favorite dirt roads. The dirt roads by my childhood home, leading to the trees I used to climb and the pond where I caught tadpoles. The dirt roads to my family farm, where I fed cows in the winter and cut hay in the summer. The dirt road up the canyon, where we herded cows every spring and went camping as a family.

I even began photographing my own favorite dirt roads as an homage to Robert Kinmont’s piece. I have since abandoned the project, but I may return to it in the future. The idea still makes me feel something, and I want to pass that feeling on in my own work.

I know such a project won’t resonate with everyone, but it will resonate with some. Maybe we shouldn’t always be concerned with getting that perfect shot, that photograph or artwork that will be loved by the masses. Maybe we should just focus on what resonates with us. We may not sell as many pieces that way, but art isn’t really about sales, is it?