Using 750nm IR Goggles to View Processed Color Negative Film Safely

Can 750nm infrared (IR) goggles be used to view processed color negative film without affecting unprocessed film?

Cyan Dye Absorption in Color Negative Film

Cyan dyes in color negative films typically absorb red light ranging from 620 to 700nm, and they exhibit some absorption characteristics in the near-infrared (NIR) region, including around 750nm. Since you mentioned that 750nm light is partially absorbed by the cyan dye, it suggests that when exposed to this wavelength, the cyan dye would not appear transparent. This property is crucial in understanding the interaction between IR light and processed color negative film.

Film Sensitivity to IR Light

Color negative films generally have limited sensitivity to wavelengths beyond their specified range, which is usually around 700nm for most films. If the film does not have significant sensitivity to IR light, it means that unprocessed film would not record the 750nm light effectively. Consequently, unprocessed film would remain relatively unaffected by the IR light.

Viewing Processed Film With IR Goggles

When color negative film is processed, the dyes have already been developed and fixed. This means that the cyan dye, which absorbs 750nm light, would appear darker or more opaque under IR goggles. This allows you to see the processed film's colors and contrast without affecting unprocessed film. Since unprocessed film does not respond significantly to this wavelength, it should not be exposed or fogged by the IR light.

Conclusion

Using 750nm IR goggles could indeed allow you to view processed color negative film without exposing unprocessed film. The processed film would show variations in opacity due to the cyan dye's absorption at 750nm, while the unprocessed film would remain largely unaffected due to its limited sensitivity in that range. However, it is essential to ensure that the goggles and the specific film characteristics align with these expectations for optimal results.

Film Sensitivity Beyond 700nm

There are some films with sensitivity beyond 700nm. Filters on IR sources can have sharply cut absorption patterns or broader absorption patterns. For example, an 800nm source would be safer. At Kodak, we used a 900nm source to estimate the amount of residual silver left in the film, which was safely beyond the absorptions of the image dyes.

Additional Considerations

When using 750nm IR goggles to view processed color negative film, it is crucial to consider the following:

The sensitivity of the film to IR light. The specific wavelength and filter characteristics of the IR source. The consistency of the absorption properties of the cyan dye in different films.

By ensuring that these factors align with the expected behavior, you can minimize the risk of unintended exposure to unprocessed film when viewing processed color negative film with 750nm IR goggles.