BetterPhoto Q&A
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Why do I require........?

1. Why do color slides require a corrective filter for tungsten and flourescent light and color negative film doesn't?

2. How are additive colors used to reproduce natural colors on film?

3. Why is a 35 mm camera identified as a 35 mm camera?

Any help you can give me to answer these questions would be appreciated. Thanks

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December 03, 2000

1) Tungsten and Fluorescent light are actually different colours from daylight - your mind simply adjusts to it. When you print negs, you can do colour adjustment (though most 1 hour labs wouldn't do it for you) so that the colour comes out correctly. Because you project directly from the film in slides, there is no chance of adjustment.

2) Additive colours? You mean like blue and yellow make green? (as opposed to subtractive colours, like light?) Not really sure what your question means... Is it talking about the development process?

3) A 35mm camera is called such because the film size is 26mm x 35mm (actually only 24mm usable on the other axis, the rest is sprocket holes).

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December 03, 2000

Here's some additional information about (2) and (3).

2) There are three emulsion layers in color film. In color negative, they're Cyan, Magenta and Yellow. In color transparency (slide) they're Red, Blue and Green. Any color in the visible spectrum can be created by some combination of the intensity of these three colors. The relationship between the negative and positive (transparency) colors is:

Cyan = Blue + Green
Magenta = Red + Blue
Yellow = Red + Green

Red = Magenta + Yellow
Green = Cyan + Yellow
Blue = Cyan + Magenta

Cyan is the negative of Red.
Magenta is the negative of Green.
Yellow is the negative of Blue.

3) The Kodak "number" for 35mm film size is 135. 35mm film is the width of the film strip itself, from edge to edge. The frame size on the film is 36mm wide by 24mm tall. Add the sprocket holes to the 24mm height fits between the sprocket holes. 35mm film was originally called "Edison Size" because its 35mm width and the sprocket holes were originally created by Thomas Edison for use as motion picture film. In creating his original motion picture system, Edison ordered long spools of 70mm film from Kodak and asked Kodak to slit them down the middle into a pairs of 35mm wide strips. 70mm film was a common size for still photography at the time (and you can still buy it). Edison's lab added the sprocket holes, in the same location, size, shape and pitch you see them on 35mm film today. The cinema frame size is 18mm x 24mm, half the width of the still camera frame size.

Several decades later during the mid-1920's Leitz introduced the Leica "A" which was the first successfully marketed still camera to make use of Edison's readily avaiable cinema film. The frame was doubled in size to allow turning the film sideways from how it would be oriented in a cinema camera, and provide a larger negative.

The earliest 35mm films used in the Leica "A" were cinema film. It was cut and spooled into reloadable cannisters in a darkroom. These cannisters are the forerunners of the 35mm cartridges used today. You can still buy empty cannisters, and long spools of bulk film to cut and load your own! Today, the emulsions used on cinema and still photography films are quite different, but 35mm cinema film is still made. Other than being a considerably longer strip of film, it looks exactly the same as what you use in a 35mm still camera. And that's the rest of the story.

-- John

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December 17, 2000