The Fresnel lens was invented by the French physicist Agustin Fresnel, who first used this design to build a glass Fresnel lens – headlamp lens in 1822. The Fresnel lens is a thin and flat optical lens consisting of a series of small narrow concentric slots on the surface of a lightweight plastic sheet to reduce the thickness, weight and cost. Each slot is at a slightly different angle to the next, and with the same focal length to focus the light towards a central focal point. Each slot can be considered as a small single lens to bend the parallel Fresnel light waves and focus the light.
They are also known under the name Blattlupe, magnifying glass, check card magnifier, magnifying glass or magnifying glass. These are thin plastic films that work much like a magnifying glass but are very thin compared to a glass optical magnifier. The principle was invented by Augustin Jean Fresnel, a French physicist. Initially, this principle was used in the illumination of lighthouses to bundle the light.
How are Fresnel lenses constructed?
These lenses consist of many concentric rings. Each ring contains a kind of step, an area where the thickness decreases. Here, the curvature of a normal glass lens is modeled. When light passes through these steps, it is broken, distracted. Refraction occurs when light passes from one medium to another. The two media involved are air and plastic in our case. If we take a close look at a magnifying glass, then we recognize the incorporated grooves with the naked eye. These steps now make this film behave like normal magnifying glass. Unfortunately, the images achieved with such a Fresnel lens are not so good, the levels worsen this.
The big advantage of Fresnel lenses is that they can be made very thin and with a large surface area compared to thick glass lenses.
Can fresnel lenses also scatter the light?
The incorporated steps can also be arranged vice versa, then from a collection of a diverging lens.
Where are Fresnel lenses used?
One of the first applications was the already mentioned lighthouse lighting. As a result, the higher the light output was possible. They are also used in headlamps for stage technology or older flashlights. The overhead projectors still found today in schools have also incorporated a large Fresnel lens on top of the support surface to focus the light.
In cars, we sometimes find such loupes incorporated or glued in the rear window. Here they act as a divergent lens and expand the field of view when looking backward. For example, they are marketed as wide-angle Fresnel lenses.
Fresnel lenses are also used in motion detectors to focus heat radiation on a pyroelectric element (gyro sensor).