Crop Factor Calculator

In short Crop factor is the ratio of full frame diagonal to your sensor diagonal, and it converts framing between formats: a 35 mm lens on Nikon or Sony APS-C frames like a 53.7 mm on full frame. That is a framing conversion and nothing more, and the single most misunderstood point in photography is what happens to the aperture. The equivalent aperture — the f-number multiplied by the same crop factor — tells you what gives the same DEPTH OF FIELD and gathers the same TOTAL light. A 25 mm f/1.8 on Micro Four Thirds is equivalent to a 50 mm f/3.6 on full frame in framing and in background blur. But it is still f/1.8 for the light meter. Exposure does not change with format at all: f/1.8 at 1/125 and ISO 400 is the same exposure on a phone, on APS-C and on medium format, because the f-number describes brightness per unit of sensor area and that is exactly what a meter measures. The f-number does two jobs at once, and equivalence is about the second one. It sets the brightness per unit area, which is why exposure transfers unchanged. And it sets the physical diameter of the opening for a given focal length, which is why total light gathered — and therefore depth of field and noise — does not. One more thing the crop factor does not carry across: perspective. That comes from where you stand.