Pinholes in stereo

Pinhole images – why be satisfied with one when you can get cross-eyed over a pair?

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A few weeks ago while spending a dull, wet weekend clearing up my photo stuff I came across a box of odd bits of Harman Direct Positive paper left over from a workshop I ran quite some time ago. I was pretty sure the paper hadn’t been handled in entirely light-safe conditions and would be fogged but rather than waste it I loaded it into a variety of cans and boxes all of which had been converted for pinhole use. When the weather improved I could have a play and see what transpired from the paper!

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Anything that can be made light-tight is potentially a pinhole camera.

One of the converted boxes had been a Father’s Day gift containing whisky flavoured truffles. Once the contents had been dealt with the true purpose of the box was realised as a two-shot pinhole camera, allowing for two separate exposures to be made before having to return to the darkroom or fumble in the dark bag for a change of paper or film. Two chambers and a frame to hold media in place was formed from foamcore, the interior was given a spray of flat black paint, two holes were cut in the lid and pinholes taped over the holes.

OLYMPUS DIGITAL CAMERA
Components of the camera

Coincidentally, I had been reading of my friend Oonagh’s endeavours in 3D imaging with an antique Wray Stereo Graphic 35mm camera. It occurred to me that my two-pinhole Whisky Truffle Pincam could be adapted to make a stereo pinhole camera.

To make images suitable for viewing as a stereo pair, they need to be taken of the same view but from viewpoints slightly apart. That is taken care of by the two adjacent pinhole apertures. The exposure given to each needs to be as near as possible the same – that will depend on how well I can make two equal pinholes!

Ideally to view the 3D effect requires a stereoscope which optically overlaps the images so that the viewer sees a virtual third 3D image. However at the cost of a little discomfort, By squinting at the two images they can be made to overlap in the same way. This would do me for now!

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test stereo shot on old, fogged paper

The original pinhole apertures were just as they had been made. In true pinhole fashion there had been no attempt to match them. My first test stereo image confirmed that my Direct Positive paper was indeed fogged but as my purpose was to compare the differences in aperture, the expected fogging was not important. More significantly, the first pair of images show that the Right pinhole (the one on the left!) was wider than that on the Left (the one on the right!). This would need to be corrected if I was to make a successful stereo image pair.

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result of enlarging the pinholes in an attempt to balance them

Having made my initial assessment, I decided to balance the apertures by attempting to enlarge the Left pinhole just a smidge. Of course having made the intended adjustment I felt the smidge was perhaps a tad too much and so adjusted the Right pinhole by the said tad, more or less. The result was not pleasant with both images now overexposed, too soft and neither a match for the other.

There was only one thing for it: re-make the pinholes from scratch, aiming for a matched pair. The optimum aperture diameter for a pincam with a projection distance (i.e. focal length) of 36mm is around 0.25mm so that’s what I was aiming for although size was less important than equivalence.

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high resolution scan of pinholes and millimetre rule

By laying the pinholes alongside a millimetre rule on the bed of my scanner and scanning them at its highest resolution I was able to make reasonably accurate measurements of their respective diameters and an assessment of their regularity. The Left pinhole measures 0.33mm and is quite a clean, round hole while the Right pinhole is 0.30mm, more elliptical and a bit rough on one side. With a projection distance of 36mm the relative apertures were f/110 and f/128.

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final attempt – not quite there but getting close

The difference between f/110 and f/128 would have been neither here nor there in a single exposure ‘regular’ pincam but I was surprised by the effect on the final pair of stereo images of such an apparently small difference in aperture. Ideally for a stereo pair, the exposure given to each image should be precisely the same. That said I’m satisfied with the closeness achieved.

(I had attempted in the final image to add an extra layer of depth in the form of a ghostly selfie in the gap between the foreground stump and the distant tree. Unfortunately I missed my positioning but look carefully and I can be seen directly in front of the tree!)

Author: Donald Tainsh

A lifelong explorer of photography

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