Monday, July 9, 2012

Solargraphs, or how to get a (sort of) color photo with black-and-white paper

Several years ago on "Astronomy Picture of the Day" I saw an article about Solargraphs - a topic that recurs ever year or so.  Essentially, this is a long-exposure pinhole camera set outside on a (mostly) static scene.

The technology is quite simple:
  • Empty a soup can by eating its contents.
  • Empty an aluminum soda pop can by drinking its contents - or finding someone do that for you.
  • Get black-and-white print paper from wherever - preferably not panchromatic, but use what you can find.
  • Cut a 1cm (1/2") window in the soup can
  • Cut a 3-4cm (1-1/2-2") square piece out of the middle of the side of the soda pop can
  • Punch a small (0.5mm) hole in the middle of the above piece of the pop can.  Try to make the hole as "clean" as possible.
  • Using black electrical tape, attach the piece of aluminum to the side of the soup can, centering the the pinhole over hole in the soup can.  Make sure that the attachment point is light-proof, hence the use of black electrical tape - but don't cover the pinhole!  (Duct Tape isn't necessarily light-proof so I'd avoid it.)
  • Fashion a lid for the top of the soup can.  I've been able to take the rest of the flat aluminum side of the soda can and form it over the top of the soup can (careful of the sharp edges!) and make a lightproof "hat".
  • In subdued light - preferably dim red, say from a photographic safelight, an astronomer's flashlight or a red LED (if you used Orthographic paper) cut a piece of photo paper that is about the height of the inside of the soup can and will wrap most of the way around the inside.
  • Inside the can, place the paper, the emulsion side facing toward and centered on the pinhole.
  • Using black electrical tape again, tape the "hat" on top of the can to make it light-proof.
  • Gently put a piece of tape over the pinhole.

Photographic print paper is a bit harder to get locally than it used to be:  When I got my supply, I went to a local photo shop that I'd gone to years ago to get my developing supplies and asked where they kept the paper.  Somewhat to my chagrin, I was directed to a single shelf in a corner where there was a sparse assortment of miscellaneous, dusty items.  The only good part about this experience was that everything on this shelf - including the three remaining packs of photo paper - where on sale and heavily discounted.  The paper itself was more than a year out of date, but that's really not much of a concern for black and white paper stored at reasonable temperatures and is even less important when used in a solargraph!  (On the web, it's very easy to find photographic print paper for cheap, so don't despair if you can't get it locally.)

Figure 1:
A solargraph - pointed mostly south - at my workplace.
Click on the image for a larger version.
You now have a rudimentary  pinhole camera.  Place it outside or in a window, attached to something solid that will not move (avoid a tree, if possible as it sways and bows with wind and season).  I attach it using nylon wire ties to a post, but one could duct-tape it - but make sure that it is solid and will NOT shift!  It is also best to place it such that it will not be directly exposed to rain and snow - a wooden or metal "hat" attached just above it on a pole or fence post outside would be good and don't forget to remove the piece of tape placed over the pinhole during assembly!

Now, leave it alone for several months, taking good notes on where, exactly, you left it if you happen to be placing it out of the way - say, in the woods.

It is recommended that one orients the pinhole of the solargraph such that it faces toward the sun (e.g. south for those in the northern hemisphere) but a view toward the east or west is also good.  If you live way north or south (arctic/antarctic circle) then it might be interesting to point it north (or south)-ish during the summer-ish months.

Results of some of these solargraphs may be seen in the attached images.  The above is the first solargraph that I'd done, taken by attaching a soup-can camera to a metal railing at my work in a location with a south-facing view showing the thick arc of the sun as it changed its elevation over several months in the year.  In the images are ghostly vestiges of snow and vehicles that were intermittently present during its exposure.

When I did my first solargraph I didn't know what to expect and upon removing the paper (again, in subdued, red light) the image was a bit faint, so I did what anyone would do:  I immersed the photo print paper in some warm coffee to develop it* - and develop it did, much more quickly than I'd expected!  Before I knew it, the paper had turned a very warm brown from being overdeveloped and not just from the coffee!

At this point, the image was negative, of course, so I placed it on the photo scanner and digitized it, protecting it from light beforehand:  After scanning I noticed that the paper was even darker (and of lower contrast) than before so it's best to NOT scan it more than absolutely necessary since you are, in fact, "burning" away the image by doing so!
Figure 2:
Winter/Spring exposure looking southwest from a location in the
mountains central Utah at about 8400ft (2560m) elevation.
Click on the image for a larger version.

Once digitized it's easy to invert the image and as if by magic, there's a semblance of the original scene - and, amazingly enough, in color - on black-and-white print paper!

I'm not sure exactly how the color part works, and to be sure, it really doesn't work very well so the pictures on this page have been somewhat color and contrast-enhanced using GIMP, a free image manipulation program, but I'm sure that you'll agree that the results are tantalizing, if not amazing!

The second solargraph was taken over a much longer period of time (5 months) and placed at a remote cabin in central Utah, attached to a support on a deck.  From the track of the sun one can clearly see the apparent motion of its track from the winter solstice to well into spring - a month or so shy of the summer solstice.  On the ground for much of this time was snow, but it being white its image remained even though the ground was at least partially bare for the last month or so of the picture.

With its longer and more complete exposure - and now knowing what to expect - I removed the paper from the soup can camera and placed it directly into the scanner (again, in subdued light) and after inverting and a bit of brightness/contrast/color tweaking, got the picture you can see and with the more thorough exposure, the result was much better than the first attempt.  The scene itself lacks color, but that's generally true of winter!

Again, one of the most fascinating aspects of this is that negative pseudo-color images result with the use of black-and-white photographic print paper - and without the need for any developing at all!  It's also interesting to see the changing path of the sun over a period of months - and even of cloudy days as evidenced by the breaks in the yellow sun tracks!

 * As it turns out, some of the constituents of coffee act to develop photographic film and paper - not particularly well, as it turns out, but it does work and is described on a lot of web sites.


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