Optical Effects of Stacking Camera
Filters should not be "stacked"-that is,
placed over a lens more than one at a time-for a number of reasons.
Among these is the cumulative effect of one aspect of reflected light:
light is reflected from surfaces according to its angle of incidence
(the angle at which the light ray approaches a surface).
When a light ray strikes a transparent
surface-as when passing from air to glass-at the perpendicular,
relatively little is reflected, but when it strikes at a lesser angle a
higher percentage is reflected. With any one surface this effect is
small, and it is not noticeable, in practice, with just one filter. But
if several filters are placed over a lens (each filter with two such
reflecting surfaces) the resultant light loss upon exposure may become
Furthermore, there is a tendency for such
light to be reflected repeatedly inside the filter, between its two
surfaces. This light, now disturbed from its original image-forming
path, may finally strike the film as internal flare that lowers image
contrast. Because of the angles of incidence involved, these effects
will be more noticeable with wide-angle lenses. Cumulative effects can
be quite important.