Fresnel Lens Magnifier, Diameter 200mm (7.9''), Focal Length 200mm, Acrylic Lens (not Glass), for Physics Classroom, Solar Heating, Magnifiying, Fire Starter. (Focal Length 200mm)

Excellent for demonstrating how Fresnel optics work in scaled lighthouse demos. When paired with a small, bright LED, the lens produces a convincing, highly directional beam that illustrates the principle of concentrating light for visibility at a distance. For the best effect, use a pointlike light source, keep the lens flat, and shield stray light so the beam appears crisp.

I experimented with both this bigger one and the smaller credit card size versions. The little ones did make smoke and embers, and I probably would have gotten a fire going with the little ones with a little more effort. The big one, oh yeah. I was drawing scorch marks across cardboard like it was a sharpie. Definately could have started a fire with this, if that was the intention.

it worked great to concentrate the sunlight into a dangerosly hot laser. i was able to etch my name into cocrete and get some glass to a molten state. The round design left me wishing it would have been rectangular so that it would have been easier to construct kind of a stand for it.

The Fresnel Lens arrived well-packaged, brand new, and completely scratch-free, which was a great first impression. Its magnification is impressive and works exactly as advertised. I'm currently using it as a solar death ray, and it focuses sunlight so efficiently that it instantly heats up and burns organic materials. It is perfect for high-intensity solar experiments.

Just what I wanted loads of fun

You can't tell from the images, but it's not flat like other Fresnel Lenses I've used. It is covered in circular machining (?) ridges on one side. I'm guessing this design or poor machining is what results in the lens having a terrible focal point completely useless for starting fires on tinder. I would give it 1 star but am assuming amazon lied to me in my search and/or there are variations in Fresnel Lenses that I am unaware of. They've since updated their images to show the ridging. Apparently it is a valid design. With that said, I could not get it to focus how the pictures showed with clear sun overhead. For comparison, my wallet sized Fresnel Lens produced a better focal point so the 3 stars stand.

This lens does what it's supposed to do. It is light weight.

You have to keep in mind that it is pretty small, but it can start a fire in any suitable material as long as you have bright sunshine.