Crop Factor Calculator

What Is Crop Factor?

Crop factor compares a camera sensor diagonal to a 35mm full-frame sensor. A smaller sensor crops the image circle, so the same lens looks more telephoto. A 50 mm lens on Canon APS-C behaves like about 81 mm on full frame.

Crop Factor Formula

Diagonal crop factor:

$$\text{CF} = \frac{\text{diag}_{35\text{mm}}}{\text{diag}_{\text{sensor}}}$$

35mm equivalent focal length and aperture:

$$\text{FF focal} = \text{lens focal} \times \text{CF}$$ $$\text{FF aperture} = f\text{-number} \times \text{CF}$$

Example: 50 mm at f/2.8 on a 1.62× APS-C sensor gives about 81 mm and f/4.5 full-frame equivalents.

Frequently Asked Questions

Does crop factor increase magnification?

Yes. A smaller sensor crops the projected image, so the same lens appears more telephoto. You gain field-of-view compression but lose total light collection per frame.

Why does aperture change with crop factor?

Depth of field scales with sensor size. Equivalent full-frame f-stop is the lens f-number multiplied by crop factor, which helps compare background blur across formats.

What is Canon APS-C crop factor?

Canon APS-C sensors are commonly rated at 1.62× because their diagonal is smaller than many other APS-C sensors.

Can crop factor be less than 1?

Yes. Medium and large format sensors are bigger than 35mm full frame, so their crop factor is below 1.0.

How do teleconverters affect crop factor math?

Teleconverters multiply effective focal length. Focal reducers divide it. Include adapter magnification when converting between lens specs and 35mm equivalents.

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What Is Crop Factor?

Crop Factor Formula

Frequently Asked Questions

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