When looking at an object, the highlights are usually on the corners and edges. Highlights can occur anywhere on an object, but it seems like the brightest parts are where it is the most sharp.
2
-
1$\begingroup$ Or is it a matter of contrast? $\endgroup$– FarcherCommented Mar 18 at 22:23
-
$\begingroup$ I don't know if the lights are actually brighter or not on edges, but they are definitely much more noticeable on edges. $\endgroup$– mh11111Commented Mar 18 at 22:30
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
2
In the diagram below with illuminating light coming from various sources and reflections (A,B,C,D and E) to right in this example, it can be seen some while rays between A and B are directed into the lens and focused on one point (F), rays C, D and E are at too shallow an angle and do not enter the lens aperture, so they do do not contribute to brightness observed at F. There is a limited range of angles the incoming source rays at a given point can have in order to be focused by the lens if the reflecting surface is flat as there is only one normal at any given point.
When there is a corner, (as depicted in the diagram below) there is effectively an infinity of normals close to the point being imaged and greater opportunities for there to be the exact normal required for any given source ray to be redirected into the lens and close to the focused point. While they do not follow the exact path required to produce a perfectly focused image point, there is "circle of confusion, where the redirected rays are close enough to produce a brighter but slightly blurred image of the point (a highlight) and more light arrives at the focal plane, because potential source rays that missed the lens before are now utilised. The smaller the radius of the corner, the better the focusing to a point of the collimated source rays producing an even brighter highlight as you have observed. A similar analysis reveals even if the source rays are parallel, there is still a concentrating effect near curved edges.
Another way to think of it is this. If you wanted to focus as much light as possible on a single point, you could arrange a series of tiny mirrors, each at just the right angle to direct a given incoming source ray to the point. A tight curvature corner effectively does this for you.
-
$\begingroup$ Thanks for the answer. Is this related to the fresnel effect? $\endgroup$– mh11111Commented Mar 19 at 23:00
-
$\begingroup$ I wasn't familiar with the Fresnel effect until you mentioned it, but now I have looked it up, I think it would definitely contribute to and exaggerate the effect. Rays C,D and E in the second image have a lower angle of reflection than the original A and B rays, so they reflect more light as per the Fresnel effect. Without the effect described in the answer, rays C,D and E would never enter the lens and the Fresnel effect could not contribute. $\endgroup$– KDPCommented Mar 19 at 23:39