This is a "D log E" graph for Kodak 2415 film hypered with 'Forming-gas' for 40 hours (top line), 6 hrs. (middle curve), and 0 hrs or no hypering at all (lower curve). D is density, and E is exposure; where a change from 1.0 to 2.0 is a factor of 10. Visit some astrophotography web sites to learn more about hypering and D log E graphs. Forming-gas is a non-explosive mixture of hydrogen and nitrogen; with the hydrogen fraction at or under 10% by volume. It is sold commercially in small cylinders for astrophotography by larger telescope stores, or the film can be purchased already hypered. Both black and white, and color film can be hypered with Forming-gas. |  |
The same film hypered with ammonia-alcohol: 
Note that the graphs are adjusted vertically so that the density ordinates are the same height; and note that this graph extends beyond a density of 2.5 to 3.5. |
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Hypersensitizing film increases the speed of the film, especially at faint intensities were fainter stars might not be recorded. It also reduces "reciprocity failure" where the latent image density does not increase proportionally with increasing exposure. This factor can be different for each layer in a color emulsion, and hypering film can result in a better color balance - the original colors of the object are recorded truer.
Click at the right to view or download a 1-page file on how to mix and hypersensitize film with ammonia-alcohol. | |
The ammonia-alcohol (AA) method is considerably more drastic than exposing the film to a gas. In AA hypering, the unexposed film is wound on a reel, put in a developing tank, and filled with an AA mix for 2-4 minutes. The liquid is drained, the film is dried, and then wound back on the film spool. This is quite labor-intensive and requires manipulation in the dark, and carefull handling to prevent scratches and splotches. Nevertheless, it can be done at home fast and cheap. click here to download file |
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