e. You can reduce as well as increase contrast by using color filters. One place this is effective
is in black and white copying when the original has a stain. In this case use a filter the same color but
slightly darker than the stain. The filter will pass only the color of the stain so the white or gray portions
of the original will appear similar in color to the stain, thus hiding the stain. It is important to remember
that the stain must be transparent. This technique cannot be used if the stain is opaque.
Filters penetrate haze.
a. Haze filters eliminate or reduce atmospheric haze on the negative. Haze is the blue of the sky
resulting from light reflected off the moisture in the air. At short distances the amount of haze is too
small to have any effect on a photograph. At long distances the haze may be too heavy to photograph
hills or buildings clearly.
b. You can filter out haze because it is blue and ultraviolet light. Ultraviolet is invisible to the
eye but not to the film; all films record ultraviolet light. For filtering purposes we can consider
ultraviolet light as blue light.
c. Use yellow (No. 8), light green (No. 11), dark yellow (No. 15), and red (No. 25) filters as
haze filters. These are listed in order of increasing effectiveness. The No. 8 gives the least penetration
and the red No. 25 gives the most penetration.
d. Filters cannot penetrate solid particles in the air such as dust or smoke. Anything that blocks
the light of the subject will prevent the camera from seeing the subject. Haze filters reduce haze but they
do not increase the light coming from the subject.
Polarized light. A bright spot or ghostly image caused by light reflected from a mirror-like
surface such as water, glass, or glossy painted surfaces is usually undesirable in your photograph. A
reflected image such as trees on a quiet lake often lends atmosphere to the picture but at other times the
reflected image is a distraction, particularly when it is the reflection of a lamp you are using to light the
scene. Some light sources can cause a very bright spot or reflection in a window that masks a window
display. In the case of copy photography, if you have a glossy photograph that is not flat, bright spots
can reflect back into your lens. Fortunately, a characteristic of reflected light polarization makes it
possible to filter out the reflection.
a. Besides traveling in a straight line, light vibrates from side to side, up and down, and in all
directions perpendicular to its direction of travel (fig 1-4a).