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Crop factor calculator: equivalent angle, DOF, and noise

The crop factor is usually applied only to focal length, which feeds the myth that speed doesn't change between formats. An honest conversion applies the same multiplier to three quantities at once: angle of view, depth of field, and the amount of light collected.

Input data

Result

Equivalent focal length — мм
Equivalent apertureThe aperture that would give the same background blur on full frame, at the same subject size and distance. Exposure stays the same either way — it doesn't depend on format. — f/
Noise difference, stopsHow many stops less light this format's sensor collects at the same scene exposure — simply because of its smaller area. —
Diagonal angle of view — °

Exposure doesn't depend on format: f/2.8 gives the same brightness on any sensor. The aperture equivalent only describes depth of field and noise level.

How it's calculated

  1. Crop factor is the ratio of the full-frame diagonal to your sensor's diagonal. That's the single multiplier.
  2. It applies to more than focal length: the same number rescales aperture for depth of field too.
  3. For collected light, the difference is twice as many stops, because sensor area falls as the square.

Example: Micro Four Thirds, a 25 mm f/1.7 lens → 50 mm full-frame equivalent by angle, f/3.4 by depth of field, and 2 stops less light collected.

Equivalent focal length = f·k, equivalent aperture for DOF = N·k, noise difference = 2·log₂(k) stops, where k is the ratio of the full-frame diagonal to the format's diagonal.

This is an estimate

Verify final values against current standards, the project design, and equipment nameplates.

Explained in the article Фокусное расстояние — это точка зрения

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