[lightarrow]

It heats up so rapidly there is little time for any oxidation. The steel is melting rather than burning. When you cut steel with oxygen, you are burning it in an exothermic reaction.

BTW - you can take a trip to France to see one in action (if it's still in operation.)

http://en.wikipedia.org/wiki/Solar_furnace

Edit: Come to think of it, the answer to the original question is, technically, no.

Unless you grind up the steel into small particles, it won't burn. A steel plate can only be burned in an atmosphere that is very rich in oxygen.

It doesn't have to burn completely to generate smoke, only a little part.

[Geezer]

It heats up so rapidly there is little time for any oxidation. The steel is melting rather than burning. When you cut steel with oxygen, you are burning it in an exothermic reaction.

BTW - you can take a trip to France to see one in action (if it's still in operation.)

http://en.wikipedia.org/wiki/Solar_furnace

Edit: Come to think of it, the answer to the original question is, technically, no.

Unless you grind up the steel into small particles, it won't burn. A steel plate can only be burned in an atmosphere that is very rich in oxygen.

It doesn't have to burn completely to generate smoke, only a little part.

I'm sure there is a small amount of smoke produced, but at that temperature any carbon particles (soot) will be converted into CO2 rather quickly.

BTW, despite the fact that this is quite an impressive demonstration of localized high temperatures, it's not really a very good demonstration of power production. I can burn a hole in a chunk of steel almost as quickly with my oxyacetylene cutter.

[Busky Dubbs]

So the answer is, not really with a lens, but yes with parabolic/concentrating mirrors. This article cited earlier in the thread talks of making experimental alloys and 6,000F newbielink:http://www.time.com/time/magazine/article/0,9171,909204-1,00.html [nonactive]  so certainly a steel sheet is not a problem. And yeah, smoke is from incompletely burned materials, so here they're raising it to its melting temperature, not 'burning' it with oxidation (not intentionally), like they'd do with a graphite electrode in a smelting crucible. Pours right out.

I'm still confused about the whole temperature / heating / light wavelength back-discussion.
I've wondered this for several years, and I just found out:
newbielink:http://www.3drender.com/glossary/colortemp.htm [nonactive]

My friend works in film and they're always concerned about their light source - Keno Flos, natural sunlight, filters, 10Ks, blah blah - and apparently it dates back to William Kelvin's observations of a heated block of carbon. It has nothing to do with the heat of the filament or radiant body's burning. And so now I get what people meant by "black body" - not as in a non-visible light radiation spectra, but  literally a black-bodied chunk of graphite.

The video is of an experimental parabolic concentrator, not a power-generating one; for a power generating one, they only heat a boiler as much as they want the steam temperature to be at for their turbine

otherwise they'd melt the tower..

[lightarrow]

I'm still confused about the whole temperature / heating / light wavelength back-discussion.

The concept of "Temperature" is not actually as simple as it would seem.
Temperature is a statistical concept, you can't define temperature for a single particle and not even for some. In this case the particles are photons; you must have a lot of them , and so a lot of frequencies, to define T.
In a recent discussion I had in another forum, a physics professor wrote that when a physical system A exchanges energy with another system B only by means of a perfectly monocromatic laser beam, it doesn't exchange heat...