Hi Neandertal,<br><br>Also trying to light a fire also only works from one side of the Fresnel lens although both sides work enlarging.<br><br>I have both the Credit card as the 4" by 5" model from Barnes and Nobel and they are perfect and cheap.<br>But practice a lot then it's not easy to start a fire with them, my Swedish Military Firesteel starts a fire in 15 seconds but with the Fresnel lens it takes a lot longer also depending on a decently powerfull sunshine and the right fine tinder materials.<br><br>Best Scouting wishes from Holland,<br><br>Bagheera