Crop Factor Calculator
Equivalent focal length and the aperture rule everyone gets wrong.
Work out Crop Factor. Equivalent focal length and the aperture rule everyone gets wrong. Names the misconception directly.
Full-frame equivalent focal length
75 mm
50 mm on a 1.5× crop sensor
Crop factor converts a focal length into the full-frame equivalent that gives the same view. A 50mm on a 1.5× sensor frames like a 75mm — it does not become a 75mm lens, it simply sees a smaller part of the same image circle. The aperture row is the part most conversions leave out, and it causes real confusion. Multiply the f-number by the crop factor and you get the full-frame aperture that would produce the same depth of field: f/1.8 on APS-C looks like f/2.7 on full frame. For exposure, though, f/1.8 is f/1.8 on any sensor — the same shutter speed and ISO apply. One number, two different jobs, and only the depth-of-field one gets multiplied.
How the Crop Factor Calculator works
Convert a focal length to its full-frame equivalent, and — the part most converters leave out — the equivalent aperture for depth of field. The f-number converts for depth of field and not for exposure, and confusing the two is the most common misunderstanding in the subject.
Also known as: what is 50mm on apsc · 35mm equivalent calculator · does aperture change on crop sensor · micro four thirds equivalent focal length
Frequently asked questions
What does crop factor mean?
The ratio between a sensor's diagonal and full frame's. A 1.5× APS-C sensor sees the middle portion of the image circle a lens projects, so it frames like a lens 1.5 times longer would on full frame.
Does a 50mm become a 75mm on APS-C?
It frames like one. The lens is still a 50mm — its optics, its focus distances and its light-gathering are unchanged. Only the angle of view narrows, because a smaller part of the projected image is used.
Do I multiply the aperture by the crop factor too?
For depth of field, yes: f/1.8 on a 1.5× sensor gives roughly the depth of field of f/2.7 on full frame. For exposure, no — f/1.8 is f/1.8 on any sensor, and the same shutter and ISO apply. One number, two different jobs.
Does crop factor affect low-light performance?
Indirectly. The equivalent aperture also describes total light gathered, so a smaller sensor collects less light for the same framing and f-number, which is where the noise difference between formats comes from.
What is the crop factor of a Micro Four Thirds sensor?
2×. A 25mm lens frames like a 50mm, and f/1.8 gives about the depth of field of f/3.6 on full frame.
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