Hi, I have a fresnel lens from a old big screen tv and it is roughly 1 meter square. The focal point comes down to roughly 2.5cm square (1"). On a sunny day in Hawaii I can melt copper wire after about a minute. Copper has a melting point of 1083°C (1981.4 °F) . That's some serious fun! I can also re-melt lava rocks back into obsidian. My question is: What is the general equation to figure out the maximum temperature that can be achieved assuming no losses or distortion when an area of sunlight is focused down to another area? For example, Taking 1 m^2 of sunlight and focusing it to 2.5 cm^2 the potential temperature is? Taking 1m^2 of sunlight and focusing it to .5cm^2 the potential temperature is? Taking 10m^2 of sunlight and focusing it to 1m^2 the potential temperature is? Thanks.