A word or two on crop factor:
Over the years the camera has shrunk. As film evolved its resolving power improved and smaller film formats became commonplace. In the early 1900’s a still camera using 35mm motion picture film was introduced. The 35mm film format (image size) measures 24mm height by 36mm length. Millions of 35mm cameras were sold. Because of the popularity of the 35mm, it evolved as the gold standard as to camera and lens design. This is because each format size has a “normal” when it comes to lens focal length.
Now the camera lens projects an image of the outside world on the surface of film or digital sensor. The size of the image of objects projected and the angle of view seen is a function of the focal length of the lens being used. Focal length is a measurement taken from about the center of the lens to the image plane (surface of film or chip), when the camera is imaging a far distant subject (at infinity ∞ as far as the eye can see). This distance is by tradition measured in millimeters.
An experienced photographer, familiar with his/her camera has a feel for how big or small images of objects will be and how wide or narrow view will be. These understandings are intertwined with focal length of lens being used and the size of the format. Because the venerable 35mm film camera has been around from almost 100 years, the view this format delivers with any given focal length has become the gold standard. Stated differently, the crop factor is an aid to help make a comparison as to how a vista will image using the 35mm format as the benchmark.
Each film or digital sensor format size has one focal length that will be labeled as “normal”. We compute normal by obtaining the diagonal measure of the image size (format size) of film or chip. As an example, the 35mm frame measures 24mm by 36mm, and the diagonal of this rectangle is about 45mm. If we mount a lens about equal to this value, the view delivered is said to be “normal” (matches the human experience) as to perspective. The angle of view will be about 45⁰ with the camera in the horizontal (landscape) positon. The 45mm “normal” for the 35mm format is a peculiar value, so lens makers have chosen to round this value up to 50mm for their convenience. The difference is of little consequence.
If we mount a lens shorter than normal, the image of objects will be condensed and the angle of view expanded. As a general rule, the realm of wide-angle is 70% of “normal” or shorter. For the 35mm, this will be a focal length of 35mm or shorter. If we mount a lens 200% of “normal” or longer, we enter the realm of telephoto.
The meat of this discussion is: time marches on and modern digital image sensors are shrinking. Popular today is the compact digital -- also called APS-C format. This was a failed film format of the 1980’s. It measures about 16mm height by 24mm length. The diagonal measure is 30mm. Thus a lens of 30mm focal length is “normal” as it delivers an angle of view of 45⁰ when the camera held horizontal. Wide-angle is 20mm or shorter and telephoto is 60mm or longer.
Now to compute the crop factor, we divide the two diagonal measures; thus 45 ÷ 30 = 1.5. This is the crop factor. What do we do with a crop factor? Say your buddy has a full frame camera (a nickname for the 35mm format as is Fx). You have a compact digital -- nicknamed Dx format. Your buddy mounts a 100mm lens. Your camera is 1/1.5 = 0.66 or 66% of the size of the Fx. You mount a 100 ÷ 1.5 = 66mm, and your camera delivers the same view. In other words your smaller camera requires lenses that are 66% of the lenses required by the venerable 35mm full frame.
I wish crop factor would go away. They are useless to most except gray haired 35mm knowledgeable photographers. Tomorrow’s cameras will get smaller and smaller as imaging chip technology evolves. The smaller the imaging chip, the larger the crop factor value. In future the crop factor will disappear.
The 1/2.3 image sensor is a super small imaging chip. A crop factor of 6.22 is 1/6.22 = 0.1608 x100 = 16% of the size of a full frame. If a 100mm is mounted on a full frame, then a 100 ÷ 6.22 = 16mm. In other words, a 16mm focal length on this minute format delivers the same angle of view as a 100mm mounted on a full frame.