Death Ray Fresnel Lens solar power FAQ"can you melt cans" This video illustrates the ease a SPOT Lens can melt and burn very thin metal. For some reason, a lot of questions came in about this over the past week. The thinner the material is, the less square area it has to dissipate heat collected. This lens is extremely powerful but would have a difficult time melting a 1 inch x 1 inch block of aluminum in open air.
Metal masses require a crucible to retain the heat collected or they act like a heat sink. This is why heat sinks are usually at least 3/16" thick. Also most metals become very shunt when molten ad reflect 50% of the light,