Lens Flare Tips
Glass is a problem for direct light in all situations. When you see light transfer through a window you will notice both that the light bends, and usually creates an image on the glass itself. Seeing as a film or video camera lens is made out of glass this can be a problem during production as well. This is made even more complicated by the fact that there are actually many glass pieces in a lens situation. There are then many different surfaces on which a reflection can end up occurring. When the light source ends up making an actual incident on the image, such as there is an actual reflection of the lens in the image, then this is called a lens flare.
Avoiding Lens Flare
Lens flare is a common problem that can be avoided with common cinematographic techniques. The main one is to simply get no direct light source or reflection in the shot itself. This is going to be relatively obvious to you when you are filming as you will catch a direct beam of light and notice it in the LCD or viewfinder. Lens flare can happen momentarily and you may not notice it if you do not have a very constant monitoring of the image. To avoid this you can try to perform less hand held camera use when it is bright out or where there may be many low key light sources. A still and secured camera will be less likely to pick up unintended light sources.
Applying a deep lens shade is often going to take care of your problem in general. It is hard to decide what the specifics of the lens shade you are going to need outside of the situation, but to help select the appropriate lens shade you should perform camera tests in preparation to the actual shoot. In this camera test you should approximate the lighting situation and then see what depth of lens shade solves the problem.
Anti-reflective coating is a standard on lenses so this is going to help reduce lens flare. If you are using a lens without this it is recommended to switch to one with the anti-reflective coating. Since lens flare the exposure of the mages is added to and the contrast is reduced you will be able to see how effective the anti-reflective coating is by checking out the the amount of colors you can see.