RA_pierce said:
[quote author=randomlugia link=1225885183/0#5 date=1225933581]
What exactly is the wavelength of sunlight?
Ha!
All of them.
Sunlight is coherent compared to an incandescent light bulb.
It can be made into a reasonably "parallel" beam, just not effectively as a laser.
The rays aren't scattered as with any other light source, they at least travel uniformly in one general direction.
I really don't see a point in making it into a parallel beam though.
A fresnel lens works just fine as is. Adding optics and mirrors just adds on to the cost and reduces power. And that defeats the purpose of having easily attainable, low cost, large area fresnel lenses.
And is all the frustrating alignment worth the seared flesh and corneas?
If you want to do some "long distance" burning with the sun, get a large parabolic mirror with a long focal length.
The End.
[/quote]
Yea but the mirror would have a fixed focal point and can't be turned in any direction you want. :
And yes sunlight has a pretty small divergence because of the distance, but it's still not coherent.1m[sup]2[/sup] of sunlight on the ground doesn't come just from one tiny spot on the sun, it comes from the whole surface at the same time.
You can get a pretty good idea of the divergence with a tiny circular mirror projecting a dot.You can even calculate it if you want.
BUT, even if the sun rays are nice enough to make a beam, after the fresnel lens all of that is lost.