Photographic film and photographic paper are basically a gelatin-like emulsion, loaded with light sensitive silver salts on an acetate base.
This information is also useful for digital camera users. The only real difference is that digital uses a light sensitive chip instead of light sensitive film, so there is no need for chemical processing. Digital users should read on anyway, for this will provide a great deal of information that will be useful later on.
To understand film and photo paper think of Jello on a sheet of clear plastic. The Jello has a bunch of light-sensitive salt crystals suspended in it.
THINK ABOUT SILVER, this metal is so light-sensitive it will turn black – tarnish – when exposed to light. The light sensitizes the silver and the oxygen in the air reacts with the silver that was hit by light and “oxidizes” -tarnishes – it.
NOW PAY ATTENTION!!!!
This is illustrates what a cross-section of film might look like.
The “orange” bottom layer is the acetate (film) base, and the emulsion on top is laden with silver salt crystals
Those salt crystals are sensitive to light, and when hit by light rays and then developed by chemical oxidation, those salts will turn dark.
Salts not hit by light (i.e. black or dark rays) will be washed away. Think about this until it is clear and fixed in your mind.
Below is a piece of film that has been exposed (a negative).
Below is photographic paper that is exposed from that negative.
Look at the white jersey above, his number – 84 – appears black. Now that “white” jersey appears black and the number is white.
HERE IS WHAT HAPPENED.
FIRST, TO THE FILM ON THE LEFT:
When the reflected light from #84 passed through the lens and hit the film, the white numbers sensitized the film a lot, and the black jersey reflected no light. So white numbers registered on the film and the black jersey did not. When we developed the film – by chemically oxidizing those silver salts that were sensitized by the light – the numbers became very black and the dark jersey, which reflected no light to the silver salts, came up clear and were washed away.
NOW LET’S ZOOM IN ON THIS PLAYER….
and shine some light through this “negative” to a piece of photographic paper. A lot of light will pass through the “white” (or clear) portion that is his jersey. But, because the numbers are black, they will block light from getting though to the paper, so….. when we develop the paper we get this:
A “positive” rendition of the scene… a photographic print! Because light passed through the white part of his jersey, the final print renders it black…. as it should be.
Color photography, although too complicated to go into in detail here, looks similar:
A COLOR NEGATIVE OF BRETT FAVRE
WILL PRINT UP LIKE THIS:
Color slides (transparencies) happen because the film basically has a few layers of silver salts that act as a negative and, during the processing, re-exposes the positive layers, thus giving you a positive image.
HOT TIP OF THE DAY:
The numbers and brand name you see on the edge of developed film were put there by the film maker. If those letters and numbers are not solid black … the film was not developed properly. If the characters are lighter – grayish – the film was under-developed. And, if they are VERY black, the film was over-developed.
Now, if you have the past pages well understood and fixed in your mind, it is time to get to the advanced photography goodies.