Fresnel Lens, Diameter 100mm (4''), Focal Length 50mm, Acrylic Lens (not Glass), for Physics Classroom, Solar Heating, Magnifiying. (Focal Length 50mm)

Ants and small piles of dry brush beware. Works as expected for lighting up char cloth or tinder. Need to find a decent hard case for packing in a bag so it does not get smashed around.

Purchased for emergency fire starter.Good quality, compact yet functional.Shows easily and works great for my needs.

It is small and very thin. The lens is directional. You must look through the proper side or the perifery will be distorted and pin point heat will not be there. When looking through it the proper direction it is good for its size. It will start a fire under ideal conditions.Anything larger than this item might be considered dangerous as the heat would be very high. I saw a 10" magnifying glass years ago and it would start things on fire quickly.

I figured it would be a great product but being that it's plastic and not actual glass it's a big difference and for me I prefer glass

High quality x5 Fresnel lens. Great for reading and projects.One thing to keep in mind is the focal distance. This has 100 mm. or almost 0.395 inches.I shall buy again.Thanks.

I needed it for a high school solar heating project for my son. It works well for that. It will start burning a paper as soon as you focus sunlight on it. However, the lens has a significant spherical aberration over most of the peripheral region.

Bought two of these for a science project. Came fast and intact. With a collimated source it seems the focal length was reasonably accurate at around 50cm. The transmittance (500nm visible) was estimated at around 80%, not impressive but normal for an acrylic lens.

Not a 100% 'convex lens'. Only one side is 'beveled'. You have to buy two. AND IT SHOULD BE GLASS, BUT IT IS PLASTIC.