3 ms·
They have their disadvantages though, since the angles between incident light and surface are only mostly preseved in practice: e.g. scattering from single face
by wnkrshm 7y ago
They have their disadvantages though, since the angles between incident light and surface are only mostly preseved in practice: e.g. scattering from single facet radii (due to limited manufacturing precision), the necessity of draft facets that do not serve any optical function and introduce artifacts through unwanted refraction/reflections (and even lateral light transport due to total internal reflection and refraction towards a neighbouring facet). These effects are what usually makes fresnel lenses with a large amount of cuts appear a little blurry or milky, depending on the manufacturing precision.
You can reduce the influence of the draft facets to a degree but only if you have a point-like source (e.g. large lens diameter compared to light source size). Artifacts will be more or less visible for different object points, compared to a smooth lens.
It's a tradeoff between form factor, efficiency and quality - you wouldn't use them in high-power laser optics or telescope mirrors.
- codeduck 7y agoThe benefit of a Fresnel lense is that it only needs to roughly collimate the light, not to focus an image, whereas for a telescope mirror or lense you want as much incident light to come to the focal plane at the same focal length.