About this tool
The same lens shows a different field of view depending on your camera's sensor size. This tool calculates the 35mm (full-frame) equivalent focal length and field of view based on your sensor's crop factor, and also shows the focal length that would produce the same field of view on a different sensor system. The advanced options add the actual depth of field (hyperfocal distance, near/far limits) plus a reference aperture that would look similarly deep on another sensor.
How the calculation works
Crop factor is the diagonal of a full-frame (36×24 mm) sensor, about 43.3 mm, divided by the diagonal of your sensor. The equivalent focal length is the real focal length times the crop factor, and field of view is 2 × atan(sensor dimension ÷ (2 × focal length)), calculated separately for width and height.
In the advanced options, the comparison sensor tells you which focal length gives the same field of view: your equivalent focal length divided by the comparison sensor's crop factor. The equivalent aperture multiplies your f-number by (your crop factor ÷ comparison crop factor) to show the f-number that gives similar depth of field for the same framing.
Worked examples
- The crop factors for the sensor presets are full frame 1.00, Canon APS-C about 1.61, Nikon/Sony/Fuji APS-C about 1.53, Micro Four Thirds about 2.00, 1-inch about 2.73 and medium format about 0.79. These line up with the 1.5×, 1.6× and 2× figures manufacturers usually quote.
- A 50 mm lens on a Nikon or Sony APS-C camera has an equivalent focal length of about 77 mm, with a field of view of about 26.4° wide and 17.7° tall. The same 50 mm on full frame is about 39.6° wide.
- A 25 mm lens on Micro Four Thirds is equivalent to about 50 mm. To get that field of view on APS-C (Nikon/Sony) you would need a lens of about 33 mm.
- Comparing a Micro Four Thirds 25 mm f/1.8 with full frame gives an equivalent aperture of about f/3.6, meaning background blur similar to f/3.6 on full frame for the same framing.
When to use it
Use it when switching to a camera with a different sensor size or buying a lens, to see what focal length gives your current field of view on another system. It also helps when you want to check the equivalent focal lengths quoted in photo descriptions for different sensors.
Limits and common mistakes
- Crop factor applies to field of view only. It does not change the lens's real focal length or exposure (f-number, shutter speed, ISO), so your exposure settings stay the same.
- Equivalent aperture is for comparing depth of field and background blur, not for exposure. The same f/1.8 on a smaller sensor gives deeper depth of field.
- Do not mix up the focal length printed on the lens with the equivalent focal length. Depth-of-field and astro calculators need the real focal length.
- Canon APS-C and other makers' APS-C sensors differ slightly in size, so their crop factors are 1.61 and 1.53.
- Results are approximations from standard formulas and can differ a little from real lens distortion or manufacturer-published specifications.
Guides that pair well with this calculator
Results are approximations based on standard formulas and may differ somewhat from real-world lens distortion or manufacturer-published specifications.
Frequently asked questions
How is the crop factor calculated?+
It's the ratio between the sensor's diagonal length and a full-frame (36×24mm) sensor's diagonal (about 43.3mm). This closely matches the crop factors manufacturers officially quote (e.g. 1.5x for APS-C, 2.0x for Micro Four Thirds).
What does the 'precise depth-of-field diagnosis' advanced option show?+
It calculates the actual hyperfocal distance, near/far limits, and total depth of field for the sensor, focal length, aperture, and subject distance you entered. The circle-of-confusion value used is a standard approximation based on the sensor diagonal, so real-world results can vary with print size and viewing distance.
Why is the 'equivalent aperture' different when compared to another sensor?+
Depth of field and background blur are governed by the lens's actual physical aperture diameter, not the f-number alone. When the field of view is matched across different sensor sizes, the f-number that produces the same apparent depth of field scales with the ratio of the two sensors' crop factors.