A focal length converter calculates equivalent focal lengths and f-stops across different camera sensor sizes using crop factor multiplication. A 50mm lens on an APS-C sensor (1.5x crop) produces the field of view of a 75mm lens on full-frame. This free tool converts focal length and aperture values between full-frame, APS-C, Micro Four Thirds, and other sensor formats instantly.
Key Takeaways
- Crop factor explained: Smaller sensors capture a narrower field of view, creating apparent focal length multiplication
- Common crop factors: APS-C = 1.5x (Nikon/Sony) or 1.6x (Canon), Micro Four Thirds = 2x
- Aperture equivalence: Depth of field also changes—f/1.8 on APS-C equals f/2.7 depth of field on full-frame
- Practical impact: Understanding equivalence helps choose lenses that achieve your desired results
What Is Crop Factor?
Crop factor quantifies how a smaller camera sensor reduces your lens’s field of view relative to full-frame sensors. A 1.5x crop factor means the sensor captures only the central portion of what a full-frame sensor would see, making images appear 1.5x more magnified.
This affects lens selection directly. A 35mm lens on an APS-C camera produces roughly the same field of view as a 50mm lens on full-frame. Understanding this equivalence prevents buying lenses that don’t deliver expected results.
Why Are There Different Sensor Sizes?
Different sensor sizes address varying photography requirements and budgets. Full-frame sensors offer the best low-light performance and shallowest depth of field but cost more. APS-C and Micro Four Thirds sensors reduce camera size, weight, and cost while maintaining excellent image quality for most uses.
Crop sensors also provide an advantage for telephoto work—the crop factor effectively extends reach. A 200mm lens on a 2x Micro Four Thirds sensor gives 400mm equivalent field of view, useful for wildlife and sports photography.
How to Use This Focal Length Converter
- Enter your lens focal length
- Select your current sensor size (or enter custom crop factor)
- Select your target sensor size for comparison
- View equivalent focal length and f-stop values
The converter shows both field of view equivalence (focal length) and depth of field equivalence (aperture). Both matter when comparing systems or planning lens purchases.
Understanding Aperture Equivalence
Crop factor affects depth of field, not just field of view. An f/1.8 lens on APS-C produces the same depth of field as approximately f/2.7 on full-frame. This means smaller sensors require faster lenses to achieve equivalent background blur.
Light gathering remains constant—f/1.8 is f/1.8 for exposure purposes regardless of sensor size. Only the depth of field characteristic changes with crop factor.
Free tool by: John Isaacson, Digital Marketing Strategist
Last Updated: January 2026
