It is common practice to load a home movie camera with film fabricated to operate under tungsten illumination. This is because home movies shot indoors were most often exposed via a light bar. This is a portable light source using reflector flood lamps. These output a light that is quite warm. The warmness is due to the fact that these lamps operate by heating a tungsten filament. The bottom line is: The film is expecting this warm light as opposed to daylight.

Now daylight consists of an abundance of blue and violet light. If this “Tungsten” balanced film is exposed to daylight, the results are a cold bluish image.

To make the home movie camera more flexible, it is equipped with a salmon colored correction filter. This filter modifies the naturally bluish light of a sunlit vista and converts it so that it simulates tungsten sourced light.

Why tungsten balanced film using a salmon filter for daylight operation? Any color filter will induce some light loss. Now film is naturally most sensitive to blue and violet. Indoor film (Type A or Type B) is fabricated with a higher ISO (light sensitivity) than outdoor film. This is because indoor lighting contains less blue and violet, so indoor film need to be more sensitive than outdoor film. When an indoor film is used outdoors with a corrective filter, the filter blocks mainly the blue and violet. This combination, indoor film with filter, operates at the same ISO as its outdoor counter part. For the Kodachrome film you are asking about, the ISO for the daylight product was 25, for the indoor product, the ISO was 40. Thhis indoor product operated outdoor with the proper filter at 25 ISO.

Film fabricated for outdoor use (daylight type) does not require a filter outdoors. If used indoors, we use a light blue correction filter. Such a combination lowers the ISO a lot, so this is not common practice.Type A color film balanced for movie lights no filter required.

Type A color film balanced for movie lights 3400K to use under daylight conditions mount 85A (salmon color) this is the built-in conversion filter.

Type D color film Daylight no filter under sunlit conditions.

Type D color film Daylight to use indoors with movie lights (tungsten) mount 805A blue cooling filter (not supplied with camera). Will work but due to the low ISO of this companion, not commonly used.