Though it may seem like an innocuous part of photography, aspect ratio is a basic concept that can have significant consequences if you don’t plan ahead. I have had a model’s feet cut off, for instance, because the magazine publishing the photo used a different aspect ratio than the one I submitted. If you intend to print your images in any way, understanding aspect ratio in photography is key.
What is aspect ratio?
Aspect ratio is simply a size relationship between the short and long sides of a photo. The most common aspect ratio in DSLRs today is 2:3, which is based on that of 35mm film. A 35mm negative is 24mm x 36mm in size. Simplified, this becomes 2 × 3, or 2:3 when expressed as a ratio. You may also see this ratio written as 3:2 when expressing the relationship between the long side and short side of a photo.
Most DSLRs use what is called a crop sensor. Crop sensor cameras have physically smaller sensors than full-frame cameras, but these sensors still correspond to the 2:3 aspect ratio of a full-frame sensor.
Aspect ratio and printing
So, if you want to print photographs shot with a 2:3 aspect ratio without cropping, you end up with sizes such as 4: x 6", 8" x 12", or 16" x 24". Notice that these are all slightly longer than the conventional sizes, like 4" x 5" or 8" x 10".
So where did these conventional print sizes come from? These sizes of prints originated many decades before there was such a thing as 35mm film. Older view cameras came in sizes such as 4" x 5", 5" x 7" and 8" x 10". Prints made from these cameras were not enlarged; they were contact prints made at the original negative size. Only years later was the 35mm negative format introduced and by then these print sizes had become commonplace.
How aspect ratio affects composition
As a simple illustration, let’s look at a photo shot with a 2:3 aspect ratio, which could be printed as 8" x 12" without alteration.
Now suppose we want to print this photo as an 8" x 10". This would require some cropping , as shown below.
Here’s the same photo cropped for 8.5" x 11," which requires slightly less cropping. In both examples, I am cropping from the center to make a simpler comparison. In practice, you could crop from one side of the photo.
So how do you compose your shot when you’re not sure what size you may end up needing? The simplest solution is to compose your shot and then pull back. This allows slightly more to be included in the shot and gives you more options if you find yourself needing to crop in the future. You can pull back by either stepping back or reducing your focal length if you are shooting with a zoom lens.
Other aspect ratios
You may have heard of a micro four-thirds camera. These cameras get their names in part because their sensors follow a 4:3 aspect ratio. Print sizes for these cameras that would not require cropping would include 9" x 12" and 18" x 24".
Panoramic cameras shoot at a more extreme 16:9 ratio, which is also the ratio of widescreen televisions. This ratio allows for a wider, narrower composition.
Finally, there is square format, with an aspect ratio of 1:1. This is often the aspect ratio found in medium format cameras. These photos can be printed at sizes such as 8" x 8" or 12" x 12" without cropping.
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