Making Fire Using a Condom

The more sphericle, the better the lens works. If the balloon is too big, it becomes a squashed sphere and it's focal point becomes distorted, like a line instead of a tight circle. Sometimes just giving the balloon a squeeze in the right axis will bring the light back to a nice tight circle.

Clear latex balloons, condoms and gloves are opaque untill they stretch. The focal length on these spheres is short, about one to two inches, depending on the size of the balloon.