Some telephoto cameras use a mirror rather than a lens. What radius of curvature mirror is needed to replace a 800 mm focal length telephoto lens?
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Final Answer

1.60 m1.60\textrm{ m}

Solution video

OpenStax College Physics for AP® Courses, Chapter 25, Problem 54 (Problems & Exercises)

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Video Transcript
This is College Physics Answers with Shaun Dychko. We are going to figure out the radius of curvature of a mirror that's needed to replace an 800 millimeter focal length lens. So we want to have the same focal length and for a mirror, it's going to be its radius of curvature divided by 2 and we'll multiply both sides by 2 to solve for R. So the radius of curvature then is 2 times the focal length that's 2 times 800 millimeters, which is 1600 millimeters and changing that into meters by multiplying by 1 meter for every 1000 millimeters is 1.60 meters.