Hello. I found this page: https://www.cut-the-knot.org/Curriculum/Geometry/ParabolaMirror.shtml Where can I buy such a reflector? I found only parabolic mirrors with a focus outside the reflector. An employee said to me that at the searchlight manufacturer www.Karl-Dose.de the focus could not lie inside at a parabolic mirror. He said to me that at the hotline of www.Karl-Dose.de its searchlights have the lamp in front of the reflector. Why? This costs light anyway that is lost to the insides. www.Karl-Dose.de has painted its searchlights black inside: https://www.karl-dose.de/02_Produkt.asp?ID=21669. What kind of light waste if the focus is outside the reflector. I am despair of it, I do not find such a reflector as pointed here. I need approximately 400 mm of diameters.
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