Explain Sun Glare 
Above is a picture that I took just before the sun set. Notice the prominent red blob to the left of the sun. Can anyone explain the phenomenon that creates superimposed shapes and blobs in images of the sun and other light sources, like the one above? A diagram would be much appreciated.
 A: The reason for these is mostly reflection inside the optics of the camera, both from the surfaces of the lens elements and from the structure of the lens body, diaphragm, camera body and so on.
There can be other reasons for artifacts like this: diffraction effects when the lens is stopped right down and effects due to light bouncing around inside the film or sensor, as well as (nowadays) saturation effects in sensors which can lead to odd effects.
One interesting thing about lens flare like this is that it's always there: the lens does not particularly care that it is looking at the Sun (the sensor probably does), but stray light bounces around regardless. You only really notice it like this when there is a hugely bright object -- normally the Sun -- either in the picture or just outside it, and you notice it then because the reflections become as bright as the rest of the image.  The rest of the time the reflections are not easily seen, but they serve to reduce contrast in the image as light 'leaks' from bright areas to darker ones.
Modern lens designs and coatings are hugely more flare-resistant than older ones.  People like me often seek out older lenses for their 'glow' which is, of course, just flare of variois kinds.
