Quote:
Originally Posted by Peter Ward
But a (very) long focal length lens gives you a nice big solar image, but no smoke.
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That depends on the physical aperture and FL has nothing to do with this.
From the Sun we get 1000W/m2 so a lens of given aperture will concentrate the same amount of energy, regardless of its diameter. So smoke will appear.
My 40cm Dob instantly ignites a newspaper when pointed at the Sun and no eyepiece in it.