Induced Polarization in Photography

Any material that can be used to absorb polarized light can also be used to induce polarization. Instead of using a polarizer only as a filter at the lens, you can use two - one to do the initial polarization of the light (the "polarizer"), and the other to make the effects visible (the "analyzer"). Either natural or artificial light can be polarized. Polaroid polarizing material is available in standard 16 x 20 inch sizes, and in other sizes by special order.

Reflection Control

  • Reflections can be eliminated from almost any surface if the incident light is polarized before it touches the subject. If natural light is used, interpose a sheet of polarizer between the source and the subject, being sure that it is large enough to cover the whole subject area. Place the usual polarizing filter on the camera lens, rotate it until the reflections disappear, and make the picture. If flash lighting is being used, and the angle of polarization of reflections can only be guessed at, line up the axes of the two polarizers. Most polarizers have the axis of polarization marked on them. If yours do not, look through them both while rotating one. At the point of maximum extinction of light the axes are at 90 degrees, as was shown in Figure 8-9. Mark the axes for future reference. The lamp polarizer axis should be at 90 degrees to the axis of the lens filter in order to gain maximum reflection control.

  • If you are going to use two light sources, both must be polarized. To align two such lamp filters visually, set them up separately. Place a polarizing sheet in front of one light source, and rotate the lens filter until all the disturbing reflections are gone, and turn off that lamp. Then turn on the second lamp. Leaving the lens filter untouched, rotate a second polarizing sheet over the second lamp until the reflections produced by that source are gone. Both sheets will now be correctly oriented, relative to the lens filter.

  • Reflection control using deliberately induced polarization is more versatile and complete than that done with light that has been naturally polarized by reflection. In this use the angle of the camera axis is not critical, as it is when neutralizing naturally polarized reflections.

  • It is not always desirable to eliminate every last trace of a reflection, or even to do any modification at all. Some reflections are desirable in themselves, for what they show and how they show it. If you are dealing with reflections that conceal detail on naturally wet or shiny surfaces, you may find it best only to weaken the reflection rather than eliminate it. By removing the impression of wetness or shininess, total elimination will alter the characteristic appearance of the subject. It may also be desirable to leave some trace of a covering transparent surface.

More about Camera Filter

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