Photography Calculator

Crop factor is the ratio between a sensor's size and a full-frame (35mm) sensor, and it's the conversion you need to compare lenses across formats. A Micro Four Thirds sensor has a crop factor of 2.0, APS-C is around 1.5 (1.6 on Canon), and full-frame is the 1.0 baseline. The factor exists because a smaller sensor captures a narrower slice of the image a lens projects, so a given lens frames more tightly — and that difference has to be accounted for when you say two setups are "the same shot."

Focal length equivalence is the familiar half. A 25mm lens on Micro Four Thirds frames like a 50mm on full-frame, because 25 × 2.0 = 50. This calculator generalises that to any pair of formats: equivalent focal = focal × (source crop ÷ target crop). It lets you answer questions like "what full-frame focal length matches my APS-C 35mm?" (about 53mm) without keeping a table of factors in your head.

Aperture equivalence is the part people get wrong, so it's worth being precise. The same crop factor that scales focal length also scales the aperture for equivalence — but only for depth of field and total light gathered, not for exposure. An f/1.7 lens on Micro Four Thirds gives the depth of field and background blur of an f/3.4 lens on full-frame (1.7 × 2.0), and gathers the same total light. It does not, however, expose darker: your meter reads f/1.7 as f/1.7 on any sensor, because exposure depends on light per unit area, which the crop doesn't change.

That distinction is the whole reason the calculator reports an equivalent aperture separately. When you're matching the look of a shot — the same framing and the same background separation — convert both the focal length and the aperture by the crop ratio. When you're setting exposure, ignore the equivalent aperture entirely and use the lens's real f-number. The calc covers any two of the supported formats, from medium format down through the 1" type, in either direction.