Flashing the negative:

  • Lowers contrast
  • increases toe speed, and
  • Opens filled-in shadow areas. The toe area of a color negative film is where shadow information is captured.
Non flashed vs flashed color negative film

Pre-flashing a color negative (also b&w negative) is to pre-expose the film with a tiny amount of light so as to increase the Dmin of the film, before normal exposure. This will help to bring up the low density area in the negative film a bit so some shadow details may be enhanced.

One way to pre-flash a frame of negative film is to make use of the multi-exposure function of a camera:

  1. take a underexposure of a neutral density object such as a grey card:
    • filling the whole frame with the evenly lit grey card in front of the lens
    • set the lens focus to infinity, so the whole grey area will be totally out-of-focus to avoid recording any texture of the grey card. However, you can intentionally record the texture if you want it as a special effect.
    • shoot the grey card at smallest aperture and fastest shutter speed, says f/22 and 1/1000 sec, or adding ND filters if necessary.
    • cocking the shutter without advancing the film using the multi-exposure function of the camera
  2. Now you have a frame of pre-flash color negative in your camera and you can shoot the scene normally.
  3. You will need to make multiple adjustment to your preflash setting such as increase or decrease the shutter speed to control the amount of pre-flash exposure.
  4. You will need to start the whole pre-flash process again if you want the next frame to be pre-flashed as well.

Then you send the finished film roll to processing and examine the result.

You may recall from my previous post that pull processing can also reduce the contrast of negative film but what is the difference between them?

Pull processing is reducing the developer time so as to reduce the density in highlight areas, while pre-flash is increasing the density in the shadow areas. Both will result in a lower contrast negative but pull processing will provide an image with retained highlight details and pre-flash will provide more detail shadow areas. So the images will look different.

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2 Comments

Bobby Lee · February 21, 2021 at 8:45 am

Thank you again for the useful information on pre-flash or sometimes we called pre-fogged method in pushing the sensitivity of the film in use. The only concern or problem we encountered in the olden days was colour shift. Since the tool we have used thirty or forty years ago were not as accurate as what we have nowadays, the light source as well as the length of time sometimes could not be optimised. Especially when we are using positive film. Negative films are easier to control and with its broader dynamic range the results were better.

    H M Lai · February 21, 2021 at 9:35 am

    Hi Bobby, thanks for your comment.

    Yes, personally I only recommend pre-fog in negative film which will be easier to control. Also it can be used in B/W enlarging when in the old days, when we were running out of lower contrast paper.

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