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Solargraphy

 

Solargraphy is an extremely cheap fun project which hardly costs any time at all! With solargraphy you can record the sun's path through the sky by using extremely long exposure times, ranging from weeks to even years if you have enough patience.... Below are two examples which had exposure times of just under six months, starting at the top is the sun on June 22nd (with the sun at its highest point), and at the bottom is the sun at December 6th, just two weeks before it reaches its lowest point. More examples of solargraphy can be found here.

Nearly six months of exposure.

Nearly six months of exposure.

How it works

 

Schematic depiction of a solarcam.

Solargraphy makes use of a pinhole camera and photographic paper to record the sun's path under a long period. Each day, the sun has a different path that it follows through the sky and it will therefore leave a new clear trail on the paper for each new day (or, if it is cloudy, it will leave a faint trail or no trail at all).

The sun is at its highest during summer solstice (around the 20th of June on the northern hemisphere) and at its lowest during winter solstice (around the 20th of December on the northern hemisphere).

 

The pinhole camera can be made out of almost any material and will act as a camera obscura, which is nothing more than a dark space with a tiny hole in one of the walls. This will give an upside down and mirrored image of the world outside on the opposite wall, as is shown in the scheme on the left where a box with a tiny hole is used.

If we put photographic paper on the opposite wall, then the image will be recorded on the paper. The photographic paper will be severely overexposed and therefore does not need to be developed with chemicals. And even though it is black and white paper, it will still end up with a bit of color.

 

Solargraphy and weather

 

Apart from solargraphy just being a pretty neat fun project, you can also get some information about the weather from these images. Since every stripe in a solargraph accounts for one day, you can see day by day what happened in the sky.

Below on the left you can see how clouds influence the outcome of the picture. If the stripe is completely dark, then it was cloudy on those days, while bright uninterupted stripes means sunny days. Interupted stripes means days with clouds occasionally obscuring the sun. Lastly, if the stripe is not completely dark, but has a lower intensity than a stripe on a sunny day, then the sun was only partially obscured by the clouds.

On the right is an example of how you can see the intensity of the wind. There was a small branch in this picture, and on some stripes the sun seems to go straight through the branch, which is because the branch was moving around heavily in the wind that day in stead of staying on one location. Some other stripes only cover the edges of the branch, which means it was only slightly windy that day.

Cloudy and sunny days.

The effect of the wind on a small branch.

Making the can

 

I am pretty much a newbie when it comes to making pinhole cameras so this is probably not the most optimal way, but this is how I made my pinhole cams from empty 0.5 l beer cans:

 

Building a solarcam =>
[Step A] [Step B] [Step C] [Step D] [Step E] [Step F] [Step G] [Step H]

Step A) Two empty beer cans (I know, there is only one in the picture....)

Step B) Remove the top from one of them, and the bottom from the other.

Step C) The bottom from the second can will serve as the cover for the first one.

Step D) Make a hole in the can, where you will later mount the pinhole itself. I made this hole a bit above the middle, so that less of the foreground and more of the sky is projected on the paper.

Step E) Cut a bit of metal from the second can, and carefully make a pinhole in it. I did it by pushing on the metal with a needle, giving a bump on the other side. Then I sanded the side with the bump, making the metal thinner at the point where I pushed with the needle. This process was repeated three/four times to give a hole. A bit of fine tuning with the needle gave a round pinhole. The size and shape of the pinhole can be "determined" by scanning the piece of metal with the pinhole with a scanner. By counting pixels you can estimate the size of the pinhole.

Step F) Attach the piece with the pinhole on the can, where the larger hole from step D is situated.

Step G) To give the whole thing a bit more strength I finished it off with some duct tape (where would mankind be without duct tape....). The black square is where the pinhole is situated.

Step H) Put it somewhere on a suitable location, facing south (or north if you live in the southern hemisphere).

 

The smaller the pinhole is, the sharper the image will be, but at a certain size diffraction starts to kick in, and smaller pinhole diameters will only blur the image (see more about diffraction here). Somewhere in the middle is the optimal size, which the calculator below calculates, based on the focal length and the wavelength of the light (550 nm is green light and approximately at the middle of the visible light spectrum). The focal length is the distance between the paper and the pinhole.

The value from this calculator should be treated as an approximate value, since I found at least four different formulas which all gave similar but slightly different values (this one ends up somewhere in the middle).

 

Focal length (mm):

Wavelength (nm):

Ideal pinhole diameter (mm):

Calculate!

 

The paper

 

I definitely haven't got a lot to say here, I just purchased one brand and use that one: Ilford photographic paper multigrade IV RC deluxe (satin), 12.7 x 17.8 cm.

 

Scanning and processing

 

Every time you scan the paper, it will very slightly deteriorate because of the light from the scanner (but it's really very, very slightly...), so it pays off to prepare a bit before scanning:

• Allow the photo to dry in a dark place before scanning it. The paper has been outside for a long time, so some moisture might have been absorbed by the paper.

• Remove dust from the paper with a dust blower prior to scanning. Pretty obvious, but I just keep forgetting it.

• Put some pressure on the lid from the scanner. Once again, pretty obvious, but I just keep forgetting it. Photographic paper is "stronger" than normal paper, so the pressure from just the lid might not be enough to really flatten the photo.

• For my scanner, it makes a lot of difference if I put the paper somewhere in the middle or around the edges. It looks a lot better when it's somewhere in the middle.

• Predetermine the dimensions of the scan by making a preview scan with an old photo (or something else that has the same size). Then replace the old photo with the new photo and do a real scan. This way, the original photo will be exposed to a minimum amount of light.

 

After scanning:

• Open the image and, since it is basically a negative, invert it.

• Flip it horizontally.

• Play around with the "levels" and/or "curves" function to get the desired result, as is shown on the left.

 

Water damage

 

Since a pinhole camera has a hole in it, it is almost inevitable that some water enters the can. For me, some cans gather a lot, and some don't, and I don't really know why, since I made them all exactly the same way. Fortunately, the water can give some interesting effects, so it is actually not a problem.

The blue pattern at the top is some minor water damage.

The result of a lot of water in the can => [no water damage] [water damage]

 

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