Fresnel Lens Optics - Questions & Answers

[de1979]

Hello :)
I search for some specific info about fresnel lenses.

I bought few so called "fresnel lenses" to play with light in my photography studio.
I have both real fresnel lens (wide) and just magnifical foil (narrow).

I want to project some pattern, so I put fresnel lens in front of studio reflector, and in the between I put some object, like lace fabric. The goal is to get sharp shadow, projected pattern on the wall.

Questions:

1) what's the formula for distance between reflector, object to project and the fresnel lens? I assume it is related to fresnel lens focal length.

2) What exactly happen when I join few lenses together? I was able to do it only with the magnificial foil but I noticed it works better.

3) What if I cut fresnel lens to pieces? it looks flat, but normal lens is not flat and half of the lens shouldn't work :) is fresnel lens special here?

 

[Valerie Park]

Answer: 1) The formula for the distance between the reflector, object to project, and fresnel lens is the focal length of the lens. Specifically, the distance should be equal to the focal length in order to get sharp focus. To calculate the focal length of a lens, use the formula f = (n*d)/(n-1), where n is the refractive index of the medium the lens is made of, and d is the lens's physical diameter. 2) When you join a few lenses together, you are creating a compound optical system that can magnify or reduce light depending on the arrangement of the lenses. This can be used to create a sharper image or to correct aberrations in the image. 3) Fresnel lenses are designed to be flat, so it is possible to cut them into pieces without disrupting their function. However, it is important to note that cutting the lens into small pieces can affect the quality of the image. Additionally, since fresnel lenses are typically designed to focus light in one direction, cutting them into pieces will also affect their ability to focus light.