Occasionally in a movie they will pan across a landscape with the sun in view. At a certain angle a light beam will be seen across the image and generally will have hexagon shapes scattered along this beam. This beam and shapes are an artifact of the lens (I’m sure); but what causes them. I googled around for a still picture showing these, the best I could find was here
What about the lens causes the shapes and why are they generally hexagons?
If someone else can find an image or movie showing this I’d appreciate it.
The phenomenon is called lens flare. I don’t know what dictates the shape of the artifacts, but they’re not always hexagonal; sometimes they’re not even real - being added for effect by software after shooting.
Ah. The shape of the artifacts is dictated by the shape of the lens aperture; for apertures with six blades (common), this tends to be somewhat hexagonal.
Camera lenses are made up of multiple lens elements; what you’re seeing when lens flare occurs is the surface reflections of each of those elements bouncing back and forth off each other in the lens and back onto the film or digital sensor array.
The lens flares are hexagons because the camera iris has a hexagonal apeture. With cameras with a different apeture shape, the lens flare is a different shape.
Lens flare results when light that scatters off the surfaces of lens elements passes through the aperture, and hits the photosensor. The Aperture is usually made of six metal plates, so you usually get a hexagonal flare.
I think it’s possible for lens flare to be composed of hexagonal (or other shapes) elements and circular or almost circular elements - if some of it comes from lens elements in front of the aperture and some behind
This page claims “flare” refers to a washed-out look caused by scattering, and the string of dots/hexagons are properly called “ghosts.” But I think it’s common to refer to both as flare.
You even see them on cartoons (anime) and comics - those are definitely not real. We’re so used to seeing lens flare that artists draw it in to emphasize the bright light.
One telltale sign of fake flare is if there’s an odd number of points. Even if you have an odd shape in front of the lens (say, a five-piece aperature instead of the usual six), you’ll get twice that many rays (so ten, in this case).
Just to clarify - what Chronos talking about here is diffraction spikes. Which is one of the effects that cause lens flare. But the effect the OP specifically mentioned (string of hexagonal spots) is caused by internal reflections, not diffraction. And the shape will have an odd number of sides if the aperture has an odd number of blades. This image shows both effects very clearly - 8 spikes caused by diffraction, and a string of dots created by internal reflection.
So I was following along about the hexagonal bright spots being due to the hexagonal aperature…but…then I realized the aperature is a HOLE not a reflective surface.
I can see how a pinpoint or circular spot is caused by internal LENS reflection off of the curved surfaces of the lenses, but now I’m not following how the hexagonal shape of a hole can reflect a similarly shaped bright spot.
Unless there is a lens behind the the iris that reflects this…is this how cameras are set up, with the iris between (one?) lens and the light source?
There are multiple lens elements inside the lens. Look at the front of a camera lens and you see a reflection of a patch of sky; if you look closer, you’ll see another reflection of a patch of sky off the front of one of the inner lens elements - what’s happening is that each lens element does this - it reflects a patch of light forward - lens flare is the reflections of those reflections off the back of the lens element in front of it. If that isn’t completely confusing.
I just wanted to step in and agree with this. Back during the 1960s the Space Program must have used cameras with pentagonal apertures, because I recall seeing a lot of space photos with pentagonal flares on them. Chronos is correct about diffraction images only havinf even numbers of points (as I’ve noted before on this board), but the things we’re calling “lens flares” (I’m not really sure they’re the same things everyone calls “lens flares”) aren’t diffractive images – they’re reflected images of the aperture plane, possibly not in focus.
Assume just one lens over the aperture. Some of the light coming through the lens goes through the aperture hole, and some bounces off the aperture itself back towards the inner surface of the front lens. This light will be in the “shape” of the aperture.
Much of this light passes back out of the lens, but some is reflected off the inner surface back to the aperture. Some goes through the hole to end up in the image. Some is reflected back to the front lens again…
Based on the Wikipedia entry, the term “lens flare” seems to encompass all kinds of lens artifacts including ghost images, scattering and diffraction spikes.
We’re so used to seeing lens flare that artists draw it in to emphasize the bright light.
