If you use a 200mm lens on a camera with a crop factor of 1.5, what is the equivalent focal length?

• A. 150 mm
• B. 200 mm
• C. 300 mm
• D. 400 mm

Answer: (C)

When a camera has a crop factor, it affects how wide or narrow the scene appears with a given lens. The crop factor tells you how the field of view compares to a full-frame sensor. To find the equivalent focal length, multiply the lens focal length by the crop factor. So with a 200mm lens on a 1.5x crop factor body, the same framing would be produced by a 300mm lens on a full-frame camera (200 × 1.5 = 300). That makes 300mm the correct equivalent. The other numbers don’t match because they don’t reflect that multiplication by 1.5 for the field of view: 150mm would give a wider view than 200mm on this sensor, and 400mm would correspond to a crop factor of 2, not 1.5.