Taking a squint at George

Continuing the stereo pair experiment – could I make it work with a large format camera, using consecutive rather than simultaneous exposures?

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Having made a reasonably successful attempt at stereo pair photography with a pinhole camera I felt encouraged to explore whether the 3-D effect could be achieved using the movements of a large format field camera.

My theory was that a stereo pair from a single camera could be achieved by making consecutive exposures using horizontal shift of the front standard to effectively view the subject from two adjacent points.

To test my theory I set up ‘George’, an almost life-size polystyrene head, at a metre or so from my Intrepid camera. Then I made two exposures, the first with the front standard set about 15mm left of centre and the second with it set about 15mm right of centre.

The total separation of 30mm ensured that the image circle of the offset lens would cover the film and also that at at such a subject distance, the whole of George’s head would be included in each image. The Intrepid camera allows for a maximum of about 65mm total horizontal shift so there is scope to increase the separation as long as the image circle projected by the lens allows it without vignetting. I would expect that to achieve a realistic stereo effect the ideal separation should match the average distance between the eyes which in an adult is about 64mm.

I scanned the negatives side-by-side to produce a stereo pair (as at the top of this post). I’ve since re-scanned the two images and created a print with each separated by 30mm just as they were taken. Take a squint at George to overlap the two images as a third virtual 3-D image in the centre:

20170301002-and-others

So far, so good, although I’m not totally convinced of the stereo effect with George alone. The next step would be to test my theory ‘in the field’ with near, mid and far distant subject elements. Decent weather would help too!

After a series of depressingly dreich grey weekends, my travels in search of weekend light and suitable subject matter for the task took me to the Southern Uplands and the villages of Wanlockhead and Leadhills. There I found the remains of some old buildings in a quarry beside the old narrow guage railway that once served the lead mines here and now transports tourists, in season, between the two villages. The location served my purpose and being out of season, was free of tourists! I took two sets of three images: one with the front standard moved fuly to the left, a centred exposure (which I used to frame and focus the scene), and a third with the standard fully to the right. The total separation between left and right was 65mm but of course each individual image of the set was just 32.5mm.

Here are the sets of images, each followed by a print of left and right separated by 65mm which should be viewed by squinting at the pair to create an overlapping central virtual image:

(looking north-east)

20170304001-and-others

 

(looking south-west)

20170304004-and-others

 

Do they work? – I’m not sure. The second set are probably a better subject with the metal bars sticking out of the wall and the telegraph poles giving obvious ‘depth points’. If I concentrate my focus on the central part of the merged virtual image I can see the 3-D effect but overall it does appear confused. Choosing any combination of two adjoining photos, i.e. that have been taken with only 32.5mm separation seems to work better. So much for my theory  of matching lens and eye separation!

The sun was setting over the hills to the west and the light was beginning to change quite quickly. This may be adding to the confusion as the shadows cast by the sun have moved between exposures (as have the clouds). This would not have been a problem had I been making the exposures simultaneously.

I had intended a third set which I’d like to think would have been best of the lot but by this time the light was changing so fast I realised that because of the rapidly lengthening shadows, consecutive exposures would not work. I made do with just one image.

20170304007

All of the photos here are straight, unaltered scans of the negatives. I’m quite sure they will all print better than reproduced here so whatever I might conclude about the success of the stereoscopic experiment, I still have printable, interesting negatives to play with in the future.

The stereoscopic experiment has been interesting. I have no doubt there is a relationship between lens separation, focal length and main subject distance. The mechanism for viewing is also important, my squinting to create a virtual third image being the most basic, and I imagine needs ideally to be matched to the geometry of the taking equipment. My best success was undoubtedly with my stereo pinhole camera, the size and geometry of which would match the Victorian stereographic viewers available on auction sites.

 

Author: Donald Tainsh

A lifelong explorer of photography

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