If you mount a 50mm lens to a full-frame Nikon Z8, you get a standard, natural field of view. But if you mount that exact same 50mm lens to an APS-C camera like the Sony a6700, the image suddenly looks much more “zoomed in.”
The physical focal length of the lens hasn’t magically changed. Instead, the smaller sensor inside the APS-C camera is simply capturing a smaller portion of the light circle projected by the lens. It essentially crops the middle out of the image, giving you a narrower field of view.
To give photographers a universal baseline to understand how “wide” or “tight” a lens will look, the industry uses the 35mm full-frame sensor as the standard. To find out what your lens will look like on a smaller (or larger) sensor, we use a simple crop multiplier: Equivalent Focal Length = Actual Focal Length × Crop Factor.
You’ll also see this called a focal length converter, a 35mm equivalent calculator, or an APS-C to full-frame calculator, depending on which system you’re converting between — they’re all doing the same multiplication.
35mm equivalent focal length calculator
Select your camera’s sensor format and enter your lens details below. I have also included an optional Aperture input. This calculates your Equivalent Depth of Field, which is critical for understanding how much background blur you will actually get on a crop sensor.
Does crop factor affect light or just depth of field?
One of the most common points of friction for photographers transitioning between systems is understanding what happens to their aperture on a crop sensor.
If you use the calculator above and enter a 50mm f/1.4 lens on a 1.5x APS-C body, it tells you the equivalent is a 75mm f/2.2.
Does this mean you are losing light? No.
An f/1.4 exposure is an f/1.4 exposure, regardless of the sensor size. If your light meter tells you to shoot at ISO 100, 1/200s at f/1.4 on a full-frame camera, those exact same exposure settings will yield a perfectly exposed image on an APS-C or Micro Four Thirds camera.
The crop factor multiplier only applies to the Depth of Field (background blur). This equivalence comes down to physical optics. To get the exact same framing and perspective as a 75mm lens on a full-frame camera, you’d shoot a 50mm lens on an APS-C camera from the exact same spot. However, the physical hole letting light through the lens (the entrance pupil) is smaller on a 50mm lens than on a 75mm lens at the same f-stop.
A 50mm lens set to f/1.4 has roughly the same physical opening as a 75mm lens set to f/2.2. Therefore, while both lenses gather light for exposure at their respective f-stops, they render the exact same amount of background blur.
Standard crop factors by system
- 1.0x (Full Frame): Nikon FX, Sony FE, Canon RF, Panasonic S-Series. This is the baseline standard.
- 1.5x (APS-C): Nikon DX, Sony E-Mount, Fujifilm X-Mount, Pentax.
- 1.6x (Canon APS-C): Canon EF-S and RF-S mounts are slightly smaller than the rest of the industry’s APS-C sensors.
- 2.0x (Micro Four Thirds): Panasonic G-Series, OM System / Olympus.
- ~0.79x (Medium Format): Fujifilm GFX, Hasselblad X. Because these sensors are physically larger than full-frame, the crop factor acts in reverse, giving you a wider field of view than the physical focal length suggests.
