I started a fire in my back yard using leaves and paper. I used a 2 1/8" x 3 1/4" "ITOYA POCKELENS" fresnel lens I kept in my wallet for years. Bought it in a book store. Despite late 4PM sunshine I got a flame going without using tinder in about 10 seconds by just blowing on the smoking hole created by the lens. I have a larger one about 4"x6" but a sheet isn't necessary. BTW newsprint lights almost instantly.

It's a great backup or secondary survival fire starter since it takes no more room than a credit card. Of course you need to get the fire going before sundown. Perhaps the larger fresnel would allow one to start a fire closer to sunset.