When you take digital photographs, you pay attention to composition in the viewfinder, but when you print your photos, the full image you see in the viewfinder may not be what appears on the print paper, depending on the size you choose. This is because the ratio of the paper's width to height may not match the ratio of the viewfinder's width to height. As a result, some of the captured images may be lost when it is printed on paper.
Standard Photo Print Sizes
Although there are plenty of exceptions, most photo prints are made in one of the following sizes:
Many digital camera viewfinders display images with a roughly 3:2 ratio, which means the width of the viewfinder is 1.5 times as wide as the height. This is the reason 4x6 has become such a popular print size—it has a 3:2 width-to-height ratio (when paper is viewed in landscape orientation). When you look through a viewfinder, this is the approximate size you see and usually compose your pictures with. However, the ratios are not the same for all standard print sizes and that means your image must be cropped in some instances.
When you print an image to 5x7 or 8x10 size, the ratios are different than the ratio of the 4x6 format. Prints at the 5x7 size have a 3.5 to 2.5 ratio and a width multiplication factor of 1.4 times as wide as tall.
Prints at the 8x10 size have a 5:4 ratio. The long side is 1.25 times as wide as the height. When comparing print sizes, thinking in terms of the width multiplication factor is helpful.
Standard Print Sizes and the Width Multiplication Factors
Because photo paper can be printed in either a portrait or landscape orientation, use the longest side of the paper as the width and the shortest side as the height for these comparisons with the viewfinder.
- 4x6 - 1.5
- 5x7 - 1.4
- 8x10 - 1.25
- 10x13 - 1.3
- 11x14 - 1.27
- 10x20 - 2
- 16x20 - 1.25
- 20x24 - 1.2
- 20x30 - 1.5
The best way to deal with the different proportions of photo print papers is to capture more image than you need so that no matter how the final print is cropped, you have the important part of the image.
If your camera has a viewfinder with a 3:2 ratio of width to height, you should be able to print the entire uncropped image on 4x6 paper and on 20x30 paper because they have the same multiplication factor. That assumes however that the camera's aspect ratio matches its viewfinder ratio.
About Aspect Ratio
The aspect ratio of an image—the entire actual image the camera captures—in a digital camera also has a proportional relationship. That aspect ratio is not always the same as the viewfinder ratio. Usually, the aspect ratio is slightly larger, which might work to your advantage when printing the image to paper.
Unless you want to spend a lot of time comparing your camera's aspect ratio, viewfinder ratio and the paper sizes you might use to print an image, the suggestion to capture slightly more image than you need is still the best advice for most casual photographers.