Harvey, you can not all willy nilly feed a random voltage to a modern IC device in general, let alone a lithium battery charger. The typical charging port on a NiMH NiCad or lead acid pack is connected nearly directly to the cell with only a few components. Modern Lithium systems are all IC controlled, if you can't feed it the fixed voltage it needs it will not work. Lithium's do not tolerate trickle charging the lithium plates out and the cell becomes useless, so charge control circuitry is required.
Regardless of optimal light, if you can not feed a camera type device with a VERY specific fixed voltage that can source it's needed current, it will not work. For feeding a camera that needs that kind of imput (most of them) via a solar cell you need to charge a seperate battery pack through a regulator to give the camera what it needs, you can not simply tack on a solar cell.