Given two lenses, a positive lens 1 with focal length f₁ = +200 mm, and a negative lens 2 with focal length f₂ = −60 mm, and a light detector, it is desired to combine these to make a telephoto system. This telephoto system is required to produce a real image of the Moon (at effective infinite distance with angular diameter 0.5 degree); and the real image of the Moon is required to be 5.0 mm diameter on the detector. Calculate the required separation between lens 1 and lens 2, and the distance from lens 2 to the detector.

Given two lenses, a positive lens 1 with focal length f₁ = +200 mm, and a negative lens 2 with focal length f₂ = −60 mm, and a light detector, it is desired to combine these to make a telephoto system. This telephoto system is required to produce a real image of the Moon (at effective infinite distance with angular diameter 0.5 degree); and the real image of the Moon is required to be 5.0 mm diameter on the detector. Calculate the required separation between lens 1 and lens 2, and the distance from lens 2 to the detector.