Pinhole Camera
A pinhole camera, also known as camera obscura, or "dark chamber", is a simple optical imaging device in the shape of a closed box or chamber. In one of its sides is a small hole which, via the rectilinear propagation of light, creates an image of the outside space on the opposite side of the box.
A pinhole camera is completely dark on all the other sides of the box including the side where the point is created. This part is usually painted black, but black boxes are also used for this purpose. There is also a thin screen which looks like a projector sheet, and is put in between the dark side adjacent to the pinhole.
Up to a certain point, the smaller the hole, the sharper the image, but the dimmer the projected image. Optimally, the size of the aperture should be 1/100 or less of the distance between it and the projected image.
Because a pinhole camera requires a lengthy exposure, its shutter may be manually operated, as with a flap made of light-proof material to cover and uncover the pinhole. Typical exposures range from five seconds to several hours.
(Information found at https://en.wikipedia.org/wiki/Pinhole_camera on 01.12.2015)
Here are a few examples for pinhole photography...
(Image found at https://open2view.files.wordpress.com/2013/04/siobhan-costigan-bike-pinhole-photo.jpg on 14.12.2015)
(Image found at http://www.thesocialpicture.com/wp-content/uploads/2014/10/Pinhole-Photography-Lauren-Sowter.jpg on 14.12.2015)
(Image found at https://helencoppi.files.wordpress.com/2014/03/pinhole-aacb19.jpg on 14.12.2015)
(Image found at http://www.pinholephotography.org/images/Lattice_window%20sml.jpg on 14.12.2015)
I have also looked at many design of pinhole cameras. They can be made out of anything so long as it is light proof or can be made light proof. Below are some examples of pinholes that other people have made and found successful...
(Image found at http://petapixel.com/assets/uploads/2011/04/pinegg.jpg on 14.12.2015)
(Image found at http://i.ytimg.com/vi/espROi9g2pg/hqdefault.jpg on 14.12.2015)
(Image found at https://pinholeldn.files.wordpress.com/2014/03/acarr-film-canister-pinhole-camera.jpg on 14.12.2015)
(Image found at http://www.sciencebuddies.org/Files/2420/5/Photo_img015.jpg on 14.12.2015)
(Image found at http://static1.1.sqspcdn.com/static/f/969969/16665959/1329579466840/WorkshopPinholeCamera.jpg?token=7s3hGJFXoDIBZug%2Fhuw2bF0Yx00%3D on 14.12.2015)
(Image found at http://petapixel.com/assets/uploads/2011/03/simplelegopinhole.jpg on 14.12.2015)
 
Why pinhole camera images are out of focus.
| MAKING THE PINHOLE
The primary influence on the technical quality of a photograph taken using a pinhole camera is obviously the hole. In order to achieve the sharpest photograph, the hole must be of the optimum size, perfectly round and should be made from the thinnest material. However, the truth is that the quality and size of the hole are not such critical parameters as one might think at first glance. Interesting pictures can be taken using almost any hole. Also, sharpness alone does not always have to be the most important requirement. Photographs from a pinhole camera are always a little less sharp and sometimes a certain amount of blur can, in itself, be an attractive means of expression.
Optimal pinhole diameter
The principle of the pinhole camera ensures that the image of a point is, in fact, a small disc. The smaller the hole, the smaller the disc and hence the sharper the image. However, this is only true up to a point. If the hole is too small, then light is diffracted and the image becomes less sharp. Hence, an optimum hole diameter exists for each focal length (distance from the hole to the light-sensitive material) which will create the sharpest picture.
Most probably, the first person to try to find a formula for calculating the optimum hole diameter was the famous mathematician and physicist Josef Petzval in the mid-19th century. It was later improved by the British Nobel Prize-Winner Lord Rayleigh. The equation, on which he worked for ten years and which is valid to this day, was published in his book Nature in 1891. Several more formulas have appeared since that time, often derived from the same base.
The formula proposed by Lord Rayleigh, revised so that the result gives the diameter, not the radius, can be written as follows:
d – pinhole diameter
f – focal length
l – wavelength (usually the wavelength for yellow/green light 0.00055 mm is used)
To make the calculation of the optimum hole diameter or the optimum focal length easier, you can use the PinholeDesigner program.
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Microphotograph of a 0.2 mm pinhole.
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Making the pinhole
Several companies sell precise holes of various diameters, normally made in high-grade materials using lasers (see links). However, anyone can make a good hole by themselves.
A piece of metal cut from a drinks can, approximately 4 x 4 cm, is sufficient. First, using coarse sandpaper, remove the paint from the area where the hole should be, and try to make the metal as thin as possible. Then finish the surface by using fine sandpaper. Place the plate on a flat wooden block and, using a sharp needle, make the smallest hole possible. Be careful not to injure your hand and use a hard block to press down on the needle. Remove the embossed material from the reverse side of the plate using fine sandpaper. Place the needle into the hole again and, by gently pressing and turning the needle between your fingers, make the hole round. Smooth the hole again using sandpaper. It is necessary to repeat the process until the required diameter is achieved. A regular round hole in a very thin plate can be made with a bit of patience.
Measuring the pinhole
There are several ways to measure a hole like this. The simplest is to use a magnifying glass and ruler. However, a more accurate method is to use an enlarger. Place the hole plate and a transparent ruler in the film holder and project the image onto white paper. The greater the enlargement, the greater the accuracy of the measurement. A simple calculation will give you the scale of enlargement and, from that, the size of the hole. The following example illustrates this method: The projected image length of 6 cm of the actual ruler is 60 cm. 60/6 = 10, therefore the image is 10 times greater. The size of the projected hole image is 3 mm, 3/10 = 0.3, hence the actual diameter of the hole is 0.3 millimetres.
f number
In order to set exposure times, you have to know the f number of the pinhole camera. This is calculated simply by dividing the focal length by the diameter of the hole. However, it is important to bear in mind that, during longer exposures, the time must be extended due to reciprocity failure (see Determining exposure times for pinhole cameras).
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(Information found at http://www.pinhole.cz/en/pinholecameras/pinhole_01.html on 14.12.2015)
DETERMINING EXPOSURE TIMES FOR PINHOLE CAMERAS
Determining the correct exposure time for a pinhole camera is truly a hard nut to crack. The situation is complicated by small apertures (high f numbers) and long exposure times, and in their calculation, the reciprocity law failure (Schwarzschild effect) must also be taken into consideration. Before I describe how to calculate correct exposure times, I would like to point out one important fact. Taking photographs with a pinhole camera is always something of an experiment and requires a bit of playing around. Achieving perfect results is not always the most important aim and certain insufficiencies in the exposure do not therefore lead to a fatal mistake. Many "pinhole" photographers successfully simply use estimated exposure times and leave the light meter at home in the drawer. Also, many commonly used films have high exposure latitude and therefore are, to a certain extent, less sensitive to incorrect exposure times.
However, if we want to minimise the risk of poor-quality photographs, it would be helpful to be able to calculate exposure times as simply as possible so that one has more time to concentrate on the photograph itself and also so the whole process does not become a mathematical nightmare. One option is to prepare a simple table for each pinhole camera whereby the time measured by a light meter can be quickly converted to the required time for the given pinhole camera and film stock. You can use the PinholeDesigner program to help you with the following calculation.
f number
In order to calculate an exposure time, it is important to know the f number of the pinhole camera. Compared with normal cameras, it does not change (the hole is the same size) and the calculation is simple: the distance from the light-sensitive material divided by the diameter of the hole. For example, the formula for a pinhole camera with a focal length of 100 mm and a pinhole 0.4 mm in diameter is: 100/0.4 = 250, hence the f number is 250.
However, the problem is that the high f numbers common on pinhole cameras are not available on the majority of light meters. The only way round this is to set the light meter to a different aperture, usually f 22, and then convert the measured exposure time for the aperture of the specific pinhole camera. This is done by dividing the f number of the pinhole camera by the f number set on the light meter; this number is squared and the result is used to multiply the measured exposure time. For example, if the measured exposure time for f 22 is 1/60 second, the calculation for our pinhole camera with an f number of 250 is: (250/22)2 = 129. The measured time is increased 129 times, therefore the exposure time for the pinhole camera will be 2 seconds (rounded).
Reciprocity law failure (Schwarzschild effect)
Originally it was accepted that the photochemical change is caused only by the amount of absorbed radiant energy which is proportional to the sum of the amount of light and the length of time the material was exposed to this light. The relation between the photochemical reaction and the amount of absorbed energy is therefore directly proportional. However, research by several scientists, including K. Schwarzschild, showed that this reciprocal rule does not apply when light intensity is low. In reality, low light levels over a longer period have less effect than strong light levels over a shorter period, even though the sum of light intensity and exposure time is the same.
What does this mean in practice? For long exposure times, usually for exposures longer than several seconds, it is necessary to extend the measured time. The additional time is different for each type of light-sensitive material and for each measured time. The majority of film stock manufacturers indicate in their technical specifications by how much the exposure times should be extended; if not, then the only way to achieve correct exposures is experience.
Tips for correct exposures
Choose a material with high exposure latitude, this increases the probability of obtaining a useful negative despite certain mistakes during exposure. In general, conventional light-sensitive layers (which do not use T-grain emulsions) have a higher exposure latitude, such as Ilford FP4 Plus, and also the majority of commonly used colour negative films.
It is very difficult to set the correct exposure time for interiors where the lighting conditions are generally not so good. In most cases, the times are very protracted, often more than one hour. Usually, the only possible method to obtain a correct exposure is trial and error.
When it comes to setting exposure times, the use of photographic paper instead of negative material would require a separate chapter. The light sensitivity specified by manufacturers is measured in a completely different way than for film, and is unfit for our purposes. The sensitivity of the photographic paper should be tested. The light meter should be set to somewhere between 2 and 10 ISO.
Obviously, during exposure the pinhole camera must not be moved, otherwise the picture will be blurred. If the pinhole camera is light and cannot be fixed to a tripod, it should be weighed down.
As I mentioned previously, a good idea for simplifying exposures is to create a table for each pinhole camera and each type of film stock. The table for our example pinhole camera might look like this:
Example of an exposure table for a pinhole camera with f number 250
To take a photograph, just measure the scene to be photographed with the light meter set to f 22 and then, in the row for the measured time, look up the time for the given pinhole camera and film stock.
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(Information found at http://www.pinhole.cz/en/pinholecameras/exposure_01.html on 14.12.2015)
It was really fun to make our cameras, I made a simple one two years ago using an old shoe box that I made light proof and a piece of tin with a hole in using a pin.
This time I have decided to use a bigger box, a lens and put a sheet of curved card inside at a certain depth to try and get the focus as crisp as possible.
I started with a box that I covered in black duck tape to make it light proof. I then painted the inside using matt black paint to stop any light bouncing around inside when the shutter is open. Next I cut a square hole in the top of the box and added a piece of 2mm thick aluminium with a 2mm hole in the middle of it. I made sure that was firmly stuck in place by using more black duck tape.
By this point I had realised I had a problem, the sides of the box were starting bow in under the pressure from the tape and being weakened by paint, so I had to reinforce it. I cut a box up which was made of even thicker card than mine and for ease I covered it in black paper to make the process quicker. I then stuck them into the box which made a huge difference.
Before attaching the lens (a magnifying glass) to the top of the lid where the hole was, I measured the focal length of it which was 24cm. I measured it by using a normal ceiling light, a ruler and a flat surface directly below the light. I moved the magnifying glass up and down until the light shining through looked like it was in focus. It came through onto the table looking the same shape as light fitting above but much smaller. I then looked to see how far up off the table it was in focus and measured it to the middle of the glass of the lens. This is how deep I need my box to be to get the most in focus image. I then stuck the lens to the lid with black duck tape above the hole. I then had to try and place the thick black card into the box 24cm away from the lens, taking into consideration that the box lid was 3mm thick and the middle of the lens sat 3mm above the the lid so I needed to go 23.4cm deep into the box for it to be correct.
I cut and stuck the thick card in at the right depth to make it a curve and then moved on to the next part of the project.
The shutter came next. Using a paint holder pot with a screw lid from Wilkos, I cut the pot in half, covered it in black duck tape and attached it to the front of the box using more duck tape. Once I had finished that I finished the lid of the box by covering that in black duck tape.
The final thing to do was try it out. I took my box into the darkroom and loaded a piece of light sensitive paper onto the curved card using a small amount of bluetac.
That was the camera already to go. All I had to work out then was how long to expose for and hope my pinhole was light proof.
Working out the exposure time is not easy but was do-able. You need a light meter to help you with it. The ISO of the light sensitive paper is 100. The distance from the pinhole to the paper is 24cm (240mm) divide that by the size of the hole (2mm) so 240 / 2 = 120. That is my f/stop. The light meter doesn't go up to f/120 so I had to divided that by 2 to get a number that is on the light meter, which was 60 and then half that again to make 30.
I decided an exposure time of 45 seconds was a good place to start. I went outside to the front of the Adam's Building and set my box up on a step, exposed for 45 sec and took the box back into the dark room. I took the paper out of the box under red light and started the developing process. The paper had to go into the developer for 1 minute, then into the stop bath for 30 seconds, followed by the fixer for 5 minutes. After that it goes into the wash for 10 mins and finally to dry. Once dried you can scan it into a computer and invert and flip the image.
For the first image the 45 second exposure time was almost perfect. I was very please with the outcome and also found that the image was more crisp than without the lens using my original pinhole.
The second image I took was in a different location and didn't turn out very well. The light level didn't appear to change so I thought with being under a couple of branches to change the exposure time to 50 seconds to compensate for them however that was not long enough so the image came out very underexposed. I think it would have make a good image if I had used the light meter to check it properly.
Here are the pictures of my pinhole camera...
By this point I had realised I had a problem, the sides of the box were starting bow in under the pressure from the tape and being weakened by paint, so I had to reinforce it. I cut a box up which was made of even thicker card than mine and for ease I covered it in black paper to make the process quicker. I then stuck them into the box which made a huge difference.
Before attaching the lens (a magnifying glass) to the top of the lid where the hole was, I measured the focal length of it which was 24cm. I measured it by using a normal ceiling light, a ruler and a flat surface directly below the light. I moved the magnifying glass up and down until the light shining through looked like it was in focus. It came through onto the table looking the same shape as light fitting above but much smaller. I then looked to see how far up off the table it was in focus and measured it to the middle of the glass of the lens. This is how deep I need my box to be to get the most in focus image. I then stuck the lens to the lid with black duck tape above the hole. I then had to try and place the thick black card into the box 24cm away from the lens, taking into consideration that the box lid was 3mm thick and the middle of the lens sat 3mm above the the lid so I needed to go 23.4cm deep into the box for it to be correct.
I cut and stuck the thick card in at the right depth to make it a curve and then moved on to the next part of the project.
The shutter came next. Using a paint holder pot with a screw lid from Wilkos, I cut the pot in half, covered it in black duck tape and attached it to the front of the box using more duck tape. Once I had finished that I finished the lid of the box by covering that in black duck tape.
The final thing to do was try it out. I took my box into the darkroom and loaded a piece of light sensitive paper onto the curved card using a small amount of bluetac.
That was the camera already to go. All I had to work out then was how long to expose for and hope my pinhole was light proof.
Working out the exposure time is not easy but was do-able. You need a light meter to help you with it. The ISO of the light sensitive paper is 100. The distance from the pinhole to the paper is 24cm (240mm) divide that by the size of the hole (2mm) so 240 / 2 = 120. That is my f/stop. The light meter doesn't go up to f/120 so I had to divided that by 2 to get a number that is on the light meter, which was 60 and then half that again to make 30.
I decided an exposure time of 45 seconds was a good place to start. I went outside to the front of the Adam's Building and set my box up on a step, exposed for 45 sec and took the box back into the dark room. I took the paper out of the box under red light and started the developing process. The paper had to go into the developer for 1 minute, then into the stop bath for 30 seconds, followed by the fixer for 5 minutes. After that it goes into the wash for 10 mins and finally to dry. Once dried you can scan it into a computer and invert and flip the image.
For the first image the 45 second exposure time was almost perfect. I was very please with the outcome and also found that the image was more crisp than without the lens using my original pinhole.
The second image I took was in a different location and didn't turn out very well. The light level didn't appear to change so I thought with being under a couple of branches to change the exposure time to 50 seconds to compensate for them however that was not long enough so the image came out very underexposed. I think it would have make a good image if I had used the light meter to check it properly.
These are my two images taken using the pinhole camera. I have scanned them onto my computer at 600dpi to make it a decent quality image. Below are the images once they had been edited on photoshop. I turned the image the correct way round, invert it and then use levels and curves. Once I had got to that stage I saved the second image as there wasn't anything else I could do to improve the image. However the firs image could be edited further. As you can see on the final edit below I have added a black and white adjustment layer and used the dodge tool to get rid of the white glow from the bottom of the image. I am very pleased with the outcome and can say that I am surprised how much of a difference the lens made.
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