Do I use the ACTUAL FOCAL LENGTH or the 35MM EQUIVALENT FOCAL LENGTH for depth of field calculations?
Always use the ACTUAL focal length when calculating depth of field. Usually, the actual focal length is printed on the front of a lens’ barrel. Sometimes the length is printed on a digital camera body. The actual focal lengths of many digital camera lenses are listed here. DO NOT use the 35mm equivalent focal length for depth of field calculations. Be sure to use the appropriate circle of confusion for your camera. • What is the circle of confusion for my lens? See the “Circles of Confusion For Digital Cameras” page. There is also a circle of confusion calculator on the “Circles of Confusion For Digital Cameras” page for cameras not listed there. Suggested circles of confusion for other formats are: Format Circle of Confusion (mm) APS 0.025 35mm 0.030 645 0.045 6×6 0.045 6×7 0.060 6×9 0.070 4×5 0.100 5×7 0.150 8×10 0.200 • What is the meaning of circle of confusion? Circle of confusion is difficult to explain in non-technical terms. You shouldn’t worry about it if you’re just beginning
