Re: focus

For a pop can stove, one could mark the focal length on the side of the can for furture reference.

A piece of wire could be fashioned, bent into an "L" shape and held in place with either a ranger band or duct tape. That would save your grip as well as keep the tinder in the right spot. Perhaps a thin twig could hold the tinder in a pinch too. If you choose a thin, green branch and bend but don't break it all the way through, into a 90 degree angle. Use a tab of duct tap at the bend as a brace to hold the angle as the twigs tendancey will be to bend back.

Just some thoughts