Well, I wouldn't have thought to get serious responses to this thread. I had intended it more as a little bit of light entertainment - and seem to have mostly succeeded

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But to address the serious comments. There is actually a big advantage to use a big ballon over a small magnification lens. A condom can be blown up to a ballon of easily 8" or more, with a very large curvature. The large diameter and large curvature will collect a lot more sunlight than a small magnification lens. The technical term for this is the "numerical aperture" or NA of a lens, and you would have lug around a pretty large lens to have comparable NA. The solution here is of course a Fresnel lens: Cheap, light and can be made pretty large.
Ok, back to the much more entertaining innuendoes

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