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STEREO PINHOLE PHOTOGRAPHY
Preflashing Harman DP Paper
Out of the box, Harman DP Paper compresses the
dark tones, resulting in loss of shadow detail.
Preflashing the paper is recommended to overcome this problem.
The grayscales above illustrate the difference in tonal rendering of
a sheet of Harman DP paper which is not preflashed vs preflashed.
Not preflashing produces "blocked" shadows with
little or no detail, and a print with an overall "contrasty" appearance.
Preflashing significantly reduces blocking in the shadows,
and produces a more continuous-toned print.
Above are images from the Ilford/Harman DP datasheet illustrating the effect of preflashing.
Through trial and error, I determined the appropriate
preflash exposure for Harman DP paper is:
1.2 LUX-SECONDS.
This annotated Harman DP response curve shows the effect of preflashing.
The lower left corner highlights the flat section where the dark tones are compressed.
Preflashing biases the response to the start of the curve's "knee" so that
exposure of the actual scene will be over the more linear part of the curve.
To accomplish accurate and repeatable preflashing, I use:
1. A small white LED night light (Home Depot).
2. A photometer capable of readings down to 0.01 Lux (Amazon)
3. A darkroom timer (Ebay)
Here is the preflash arrangement in my makeshift darkroom.
The night light is positioned 50.5 inches directly above the center of the paper surface,
and is plugged in to the "Enlarger" outlet of the darkroom timer.
Using the photometer, the preflash illumination measures 0.40 Lux at the paper surface.
I therefore set the darkroom timer to 3 seconds, for the desired preflash exposure of:
0.40 Lux x 3 Sec = 1.2 LUX-SECONDS
Each time I load a fresh pair of Harman DP sheets into the film holder,
I preflash each sheet before inserting the holder's dark slide.
The holder is then ready to mount on the camera and make exposures.
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