An 80mm focal length lens with a full frame sensor at 35mm x 24mm is used on a camera that does not have a full frame sensor, with a crop factor of 1.5. What is the equivalent focal length?

• A. 60 mm
• B. 120 mm
• C. 180 mm
• D. 240 mm

Answer: (B)

Field of view on different sensor sizes is determined by the crop factor. To find the equivalent focal length on a full-frame sensor, multiply the actual focal length by the crop factor. An 80 mm lens on a camera with a 1.5 crop factor yields 80 × 1.5 = 120 mm. So the image would have the same framing as if you used a 120 mm lens on a full-frame body. The smaller sensor crops the image, effectively magnifying the center area and making the lens appear longer in terms of field of view. The other options would not match that same framing; they would produce a wider or tighter view than the 80 mm on this crop body.