5-Pack Fresnel Lens Φ80mm(3.15") Focal Length 50mm Acrylic Optical Lense for Solar Heating,Equipment Lens,Visual Education (Focal Length 50mm)

The magnifiers measure about 8cm in diameter. The lens that I purchased has a focal length of 80mm. I used one of them for magnifying small items such as the menu at a restaurant. They are made of plastic and scratch easily so a cover is needed to protect the surface. The comparatively large diameter of the lens ensures that the sun's rays will "quickly ignite" small wood shaving for a fire while camping.

I got five 50mm focal length lenses, they work as described, but are not great as magnifiers, the image becomes increasingly distorted with distance from center. This isn't a defect, just the way large diameter short focal length fresnel lenses work. It is outstanding as a fire starter, will bene a hole in thick cardboard in seconds. Best to wear dark sun glasses, the spot is super bright, can leave a long lasting black spot in your vision. TAKE NOTE: you get five of your choice of ONE focal length; I thought I was getting five of each (20 pieces)- NOT SO.

I could not start a fire with this it was the only reason I bought it

was not much help with anything