I have one of those frensel magnifying sheets, the size of a credit card. I decided to test it, its in the doug ritter survival pack, and I couldn't get a fire going.
I got a fire going today. I took my dozier and scraped it perpendicular to a cedar tree. It was on a south facing slope so it was pretty dry. Got nice fuzzy cedar bark tinder, about the size of a golf ball. I put some slivers of birch bark in this little "nest" . I reclined down next to this and focused the rays on the cedar bark. A coal started to grow, I gave it some air, and suddenly, FIRE.
This little frensel thing is pretty good for its size. I might go get a magnifying glass to compare it to.
Glad to hear you got it to work. The Fresnel lens is primarily there to help read the small print in the Survival Instructions. Some of us need that help if we lose glasses. The primary firestarter in the PSP is the Spark-Lite and its tinder. There's likely to be little real need in an actual emergency to use the magnifier to start a fire, but you can do so under the right conditions.
As you have confirmed, it will work, but it isn't a trivial task like it is with a larger Fresnel magnifier or a conventional solid lens As you discovered, the type of tinder used will make a huge difference. You must use very effective tinder. As has been noted in this thread, dark works best, but mostly it has to be very, very flammable. But, that's only half the difficulty.
Beyond really good tinder, the other key is stabilizing the lens. Because it is flexible, you have to both manipulate it so it gives you a very small and hot pinpoint of light and you then have to steadily maintain it in that position. My experience is that it works best to comfortably brace yourself against something solid. Even better if you can support it without having to hold it.
There is no question that it is far easier to start a fire using a solid lens magnifier than a small flexible Fresnel lens magnifier, but it can be done, as you confirmed. Hopefully, these tips will make it easier for anyone who wants to try themselves. However, having said all this, far better to have other reliable means to start the fire. This is back-up to my back-up.
