As photographers, we choose many things. We select our camera bodies, lenses, filters, gear, and settings galore. Why do so many photographers settle with the natural aspect ratio of their camera sensor?
Aspect ratio is the difference between the height and width of an image. I'll admit that a large portion of photographs are composed to utilize the entire sensor, whatever that aspect ratio happens to be. When we take our photographs, we are limited by the cameras and lenses we are using. We use lenses with many different fields of view — wide, normal, telephoto — all landing on that same sensor; yet all too often, people just settle with whatever final aspect ratio the camera gives them. I see it all day long: photographers posting their images online in the default aspect ratio of their camera without a thought-about aspect ratio.
However, there are some images that I feel would be much better if cropped to an alternative aspect ratio. You may use a wide lens because of your subject width, which then leaves a lot of area at the top and bottom that doesn't quite contribute anything to the photograph.
Shoot as if You're Going to Use the Entire Image
When I compose a photograph, I always frame it as though I'm going to use the whole photo, even if I think I'll crop it to some other aspect ratio in post. I do this for two reasons. First, sometimes you end up preferring the full photo better than the crop you had in mind. Second, sometimes, I change the crop to be vertical instead of horizontal, and the extra image area helps with that.
If I think I'm going to be cropping the image to a 2:1 aspect ratio, I'll still align the horizon or subject using a pleasing method, such as the rule of thirds. When I crop to a 2:1 aspect ratio, I'll often leave out a little of the top and bottom of the image.
Consider if the Subject Is Best Shown in the Aspect Ratio of Your Sensor
First and foremost, you'll need to consider the use of the photograph. There's a big difference between social media, commercial ads, print sales, stock use, phone wallpapers, etc. If it's merely an image for social media, I'll often crop it to whatever aspect ratio I feel the image looks best. I do, however, have a preference for 2:1 aspect ratios with my landscape images; it's part of my style.
Think about this: Why should a square or round object have a rectangular crop? What is that extra space contributing to the image? Not that negative space isn't useful, it can be. However, uneven space can sometimes be distracting. For example, take an image of the eclipse of 2017:
This image could work as a rectangle crop, but it also works well as a square 1:1 crop.
I don't recall where I first heard it, but someone once said: "No one knows what you left out of the photo." This is not only true for framing your composition, but also for choosing the final aspect ratio of the image. No one needs to know that above those impressive clouds was nothing but dull blue sky. No one needs to know that right next to that beautiful flower was an ugly patch of grass. What you leave out of an image is almost as important as what you include.
Get over the fact that you're cutting down an image, and focus on what looks best. If you're producing physical prints, you'll probably be limited to the standard framing sizes anyway, and a lot of those aren't the 4:3 or 3:2 aspect ratio that your camera sensor is, so you'll be cropping. Although I prefer to sell images that are the same proportions as the original image, the reality is that people often want images that they can get an affordable frame for, such as 8x10, 11x14, etc.
With the emergence of different platforms such as Instagram and mobile phones, the old school mentality of "use the entire image" just doesn't work anymore. Heck, even computer screens are now going super-wide, so just about every platform such as mobile, standard TV, HDTV, computer screens, magazines, and websites have a different preferred aspect ratio.
The Alternative to Cropping
For those that don't want to lose precious pixels, there is an alternative to cropping: stitching multiple images together will produce high-megapixel images that have plenty of resolution.
These images don't always have to be wide panorama shots. You could also shoot multiple rows to create a large image to crop however you want. Often, I'll shoot just a three or four-shot horizontal panorama with the camera in a vertical orientation, which when stitched together, often comes out very close to the 3:2 aspect ratio as my sensor, however, at a much higher resolution. For the above, the center three 22-megapixel images become about a 50-megapixel image at almost precisely a 3:2 aspect ratio when stitched.
Don't be bound by the aspect ratio of your sensor. Just like framing your shot, when you crop, no one ever sees what you have left out of the image. Feel free to crop the image however you see fit. If that image has the feel of a wide-open expanse, a wide image may help convey that feeling. If the subject has a similar height and width, maybe a square crop would work better. Do you crop your images to a different aspect ratio than your sensor? Let me know in the comments!