Whether you are new to photography or have been doing it for a while, you have probably heard the term “crop factor.” Since there are so many different kinds of cameras and camera systems on the market today, this term is used a lot in product descriptions, marketing materials, articles, and books, and you might even hear photographers talking about it. If you need to learn what crop factor means or want to learn more about it, this article should help. Please remember that this post was written for people who are just starting out, so many of the terms and explanations are too simple.
What Exactly Is Crop Factor?
Manufacturers devised a simple method for calculating the “equivalent” focal length of a lens to make it simpler for photographers to comprehend what a lens’s field of view would look like compared to a 35mm film or full-frame camera. Since the image’s corners are cropped and discarded, a wide-angle lens is no longer as wide, but a telephoto lens makes objects look closer. The crop factor is the sensor size ratio to 35mm / full-frame format (see below). You multiply the crop factor by the lens’s focal length to get the equivalent focal length concerning 35mm film / full frame.
For instance, Nikon’s “DX” cameras have a crop factor of 1.5x; multiplying a 24mm wide-angle lens by this amount results in 36mm. Regarding the field of vision, the 24mm on crop sensor DX camera would perform much like a 36mm lens full-frame camera. In essence, if you installed a 24mm lens on this crop sensor camera and a 36mm lens on a full-frame camera, placed them side-by-side, and shot the same subject at the same distance, the field of view would be pretty comparable. Nonetheless, this does not imply that the resultant photos will be equal in appearance; altering the focal length or camera-to-subject distance may significantly impact perspective, depth of focus, and background blur.
How is the Crop Factor Measured?
The math required to calculate the crop factor is relatively easy. First, you compute the diagonal using the Pythagorean Theorem (a² + b² = c²), then divide the result by the diagonal of the crop sensor. Here is a benchmark of how to calculate the crop factor for the Nikon CX sensor:
- 35mm / Full-frame diagonal: 3⁶² + 2⁴² = 1872, hence the diagonal is 43.27 (√1872)
- 13.202 + 8.802 = 251.68, hence the diagonal of the Nikon CX sensor is 15.86 (251.68)
- Crop Factor = 2.73 (43.27 / 15.86)
The Nikon CX sensor crop factor is thus 2.73x, often rounded to 2.7x.
Conclusion
Understanding the crop factor is essential for determining which lenses to employ for a session depending on the camera’s sensor size. The simplest relationship to identify is that the smaller the sensor, the higher the crop factor and the shorter the lens’ field of vision. However, even if you fail or it appears too complicated, you can always depend on software such as AutoRetouch to crop your picture without degrading its quality.
