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STEREO PINHOLE PHOTOGRAPHY
Making the Exposure
My preferred method of measuring exposure is with a Soligor spot meter
and an 18% gray card, due to this method's accuracy and versatility.
I hold the card at arms length in front of the camera and view it through the spot meter.
I then angle the card forward and back to find the maximum reading in EV units.
I then use the chart on the side to convert from EV to the required exposure time.
I generated the chart in Excel, using the formula above.
t is the time in seconds
f is the aperture = f/229 for this camera
EV is the spot meter reading
ISO is the paper speed = 3 for Harman DP
Once the camera is on the tripod and framed on the scene,
I measure the exposure as described above.
IMPORTANT NOTE
When the sky is overcast, add 1/3 stop to the meter's EV value.
This compensates for the extra blue sensitivity of the Harman DP paper.
I then set my phone's timer to the indicated exposure time and remove the dark slide.
I start the timer, count out 5 seconds, then quickly remove the two outer pinhole caps.
When the timer finishes, I count out 5 seconds,
replace the pinhole caps, and replace the dark slide.
The film holder can then be unfastened and flipped over for the second exposure.
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