A Better Focus manufactures the Hot Spot, a concentrating solar cooker that utilizes reflective film stretched across a 4' diameter dish. A vacuum is pulled inside the dish, causing a concavity in the reflective material, focusing sunlight to a 4-6" spot of over 1000 F at a focal length of 8-10 feet. Cooking accessories are also provided. A 8' diameter version has been developed for power applications.
See A Better Focus.