It’s a well-known fact that a magnifying glass can concentrate sunlight enough to burn things. Many survival experts recommend keeping a magnifying glass in your fire kit, as well as buying a compass with a built-in magnifying glass in order to start fires without using consumables. But a recent Facebook post called that idea into question. So we set out to see if the magnifying glass on a compass can actually start a fire.
Here's what you need to know: A magnifying glass can concentrate sunlight onto tinder to start a fire. This is called "solar ignition." The larger and more powerful the magnifying glass, the easier it is. Dark tinder, like char cloth, works better than light-colored tinder. Starting a fire with the sun takes a bright, sunny day and a steady hand. Magnifying lenses on compasses can be used to start fires, but a small, cheap fresnel lens is much more forgiving.
Solar ignition is the technical term for starting fires with magnifying glasses. Bushcrafter Dave Canterbury is a big proponent of this method. He explains in *Bushcraft 101*: "From the point of view of resource management for your kit, the magnifying glass or 'sun lens' is really the best fire-starting method. If the sun is shining, you need only natural materials to make an ember."
Using a lighter or ferro rod consumes part of your firestarter, but solar ignition only uses the tinder. However, there are several conditions needed: a sufficiently powerful magnifying glass (at least 5x), a bright, sunny day, a steady hand, and dry, dark tinder. Char cloth is ideal because it absorbs heat better.
The key to solar ignition is focusing the beam of light as tightly as possible. It's something you have to practice. You want the smallest, brightest dot of light. When practicing, avoid staring directly into the light—it's like looking at the sun. Use it just long enough to focus, then look away.
If you keep a magnifying glass in your go-bag, practice with it. Once you get the hang of creating an ember, you'll need to transfer it to a bird’s nest and stoke it into a full fire. It's doable, though tricky.
Back during the fur trade, Hudson Bay sold solar-powered tobacco boxes. Men would use the built-in magnifying glass to light their pipes. Today, replicas are still available if you want to go old school.
But can a compass start a fire? In short, yes! There are many YouTube videos from reputable channels showing the technique. Dave Canterbury demonstrates starting a fire with a K&R Alpine compass, and Black Scout Survival shows how to do it with a Suunto MC-2.
I decided to try it myself. I used a Bruton TruArc 15 compass and a small fresnel lens. The compass didn’t work well with dried hay or smoker pellets, but the fresnel lens lit them quickly. I even tried matchlight charcoal, which came pre-soaked in lighter fluid. The compass failed, but the fresnel lens worked in seconds.
Notice in the photos how much brighter and larger the light from the fresnel lens is compared to the compass. While a compass can technically start a fire, it's not the most effective tool. I recommend getting small fresnel lenses in bulk—they’re cheap, effective, and easy to carry.
Interestingly, the fresnel lenses I carry only have 3x magnification, and I struggle to focus the light into a tight dot. But they still work quickly, likely due to their size. Overall, while a compass lens can start a fire, it's definitely not the best option. For real reliability, a quality fresnel lens is the way to go.
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