The simplest "lens" is a pinhole, as in a pinhole camera. If you do a ray trace using a pinhole "lens", you will see how the image is inverted.

When the original negative is exposed in a camera, the emulsion faces the lens. The image formed is inverted, and "reads" correctly through the base side of the processed negative. When a contact print is made of the negative, the image is inverted again, and the image "reads" correctly through the emulsion side of the print. A 35mm contact print is projected with the emulsion side toward the lamp, and the base side toward the lens. The analog soundtrack is on the "outboard" side of the projector (towards the operator), but ends up being on the left side of the projected image on the screen. The image on the print must be upside-down in the gate to be projected upright on the screen.

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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion