Formula
The equivalent is a field-of-view comparison:
equivalent mm = focal length × crop factor
A crop factor of 1 leaves the focal length unchanged. Depth of field and exposure stay on their own unpublished pages because they need aperture and distance, not this product.
Assumptions
- The crop factor compares the sensor with a 36 by 24 mm frame.
- The lens is mounted on the camera whose crop factor you enter.
- The result describes angle of view, not a change in the glass.
Worked example
A 50 mm lens with a 1.5 crop factor has a full-frame field of view like 75 mm.
Input definitions
- Focal length
- The focal length marked on the lens, in millimeters.
- Crop factor
- How the sensor compares with full frame. Many APS-C cameras are near 1.5 or 1.6.
Limitations
Equivalent focal length does not tell you the aperture, the depth of field, or the megapixel count.
Questions
Does the lens become a longer lens?
No. The lens is still 50 mm. The smaller sensor sees a narrower angle, which looks like a longer lens on full frame.
What crop factor is full frame?
Use 1. The equivalent is then the same as the focal length you typed.