The Pinhole Camera

The camera is not just a tool for the professionals but also a household gadget. Kids have the ability to smile to the camera at their first birthday and as amazing as the camera might be, even a dying man can also smile to the camera. The camera has introduced so many words to the dictionary lately, in the year 2013, Oxford English Dictionary (OED) announced the word selfie as the word of the year and denotes the act of taking pictures of oneself by himself. Lately, Samsung started pushing out product lines of cameras called NX which they claimed to be optimized for Wefie, I guess we can figure out wefie from the word selfie.

[The great picture taken with the help of a pinhole camera credit: wikipedia creative commons]
Before the advent of the digital camera, I think most of us might be able to guess or imagine what the first camera might look like and I tell you what, it wasn't looking funny. Initially, the idea of a camera is a device that can aid drawing. In 1558, an Italian scholar della Porta published a book called Magia Naturalis where he explained how to use a convex mirror to make projections which can help aid drawing on a paper. The pin hole camera also known as the camera obscura came later in 17th century offering a better drawing aid to the convex mirror using a lens.

Working Principle

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The working principle of the pinhole camera is a very simple one and it is based on the rectilinear propagation of light. That is to say that the pinhole camera utilizes the fact that light travels in a perfect straight line. To relate this to the pinhole camera, let's perform a simple experiment using a candle or torchlight (candle preferably) and three nicely cut cardboards. On the cardboards, make a pinhole on exact point at the center of each of the pinhole (you can use a ruler to help make a precise perforation). With the help of three stands that have equal projections when placed on a very uniform flat surface like the table, arrange perforated cardboards in straight lines equidistance from each other and in such a way that you can see through the three holes.

[credit: wikimedia]
Then place the burning candle on one end of the cardboard and observe the clear light beam emerging from the other end of the cardboard. Now slightly shift the cardboard in the middle and observe that the beam of light initially emerging from the other end of the cardboard has disappeared. This is due to the fact that light travels in straight lines.

Just as the experiment above is simple to setup and the outcome easy to understand so also is the simplicity in the construction and working principle of the camera. The pinhole camera possesses no lens, hence the complexities of lens technology are avoided in the pinhole camera.
The pinhole camera comprises of a lightproof box containing a light-sensitive material at the opposite end of the pinhole opening. It also comprises of a shutter which is opened to allow a certain amount of light (determined by the size of the pinhole) to enter the light proof box and imprint an image on the light-sensitive material. The resulting image appears inverted due to the rectilinear property of light explained above.

Generally, the smaller the pinhole made on the lightproof box, the sharper the resulting image but when the hole is made too small, it could result loss of focus on images due to the fact that light rays falling at the edges of the too tiny hole may scatter causing image distortions. The focal length of the camera is the distance measured between the pinhole and photographic material placed at the opposite end of the box.

When this focal length is made small, the resulting image would have a wide angle and short exposure time while long focal length will result in telephotos and also longer exposure times.

Images taken with pinhole camera

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The pinhole camera is also known as camera without lens and with this the meaning is glaring, the pinhole camera does include lenses in its design. This also means that images taken with pinhole camera remain purely rectilinear and free from lens distortion. There are basically two types of image distortion one already stated (optical distortion caused by the lens) and perspective distortion which is caused usually due to the position of the camera with respect to the subject in focus. Perspective distortion can be reduced easily by the photographer but let’s get to know the lens distortion further. The lens distortion is subdivided into three categories and these are barrel, pincushion and mustache distortions.

Barrel distortion

When we say “barrel”, a cylindrical shape bulging in the middle comes to mind. When the photograph of a perfectly straight object or line is taken with a camera and the image appears curved either inward, we say the image surfer barrel distortion. Though lens some lenses are specially designed to have this type of optical aberration like the fisheye lens.

But one thing is very peculiar to this type of distortion and that is wide angle. When we take images in panorama mode, we experience this distortion usually towards the edges of the image but it disappears when we zoom in on the images. The image appears very normal at the middle because the image is in same optical axis with the lens but appears distorted at the edges due to a decrease in magnification as we move from the center to the edges.

Pincushion distortion

In barrel distortion discussed above, images appear distorted at the edges of the image because of the decrease in magnification moving from center to the edges. Pincushion aberration is caused due to increase in magnification towards the edges of the image. Hence we can safely say that the pincushion distortion is opposite of barrel distortion.

Also, barrel distortion comes as a result of the need to cover wide angles but here, the field of interest is small with respect to the size of the image sensor. To maintain the optical system, the image needs fit in the optical field of the camera and to do this, the resulting image is stretched pulling the image to corners.

This type of distortions is very pronounced in zoom lenses like the telephoto lenses. These are lenses possessing a longer focal length when compared to normal lenses equipping such lenses with a narrower field of view and a magnified subject. Pincushion distortions can easily be fixed in these days with sophisticated third-party post-image processing applications like the legendary Adobe Photoshop and Adobe Lightroom CC.

Mustache distortion

The most noticeable among these mentioned distortions is the mustache distortion and it so because it is a combination of the above mentioned distortion, the barrel and pincushion distortions. The distortion appears as both an inward curve at the center of the image frame and an outward curve at the end the image frame.

Mustache distortions are also known as complex distortions is the most difficult to correct among these distortions and its correction is done mainly with a very specialized post-processing software as dealing with this distortion as barrel distortion invariably creates pincushion distortion and vice versa and example of such lenses includes the Nikon 18-35mm with focal length of f/3.5 – 4.5D and this distortion appears a bit noticeable in the lens because of its wide angle.

I zoomed in on the issues associated with the camera with lenses for us to appreciate camera without lenses more. Pinhole camera images are not only void of lens distortion but every detail in the image appear in focus, this is to say that pinhole camera images possess almost an infinite depth of field.

[credit: Pixabay]
To understand the effect of depth of field in photography, the image shown above only shows one dandelion and rest of details in the picture are out of focus. Hence dept of field can be said to be the range of focus of an image. In professional photography, the depth of field can be adjusted to create very appealing images but most times, landscape photography is best taken with cameras that have great depth of field like the pinhole camera.

The pinhole camera doesn't do very well with motion images this is because the exposure time of images are usually long making motion images appear blurry and could possibly fail to capture objects moving with high speeds.

You can build your own pinhole camera!

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If there’s anything inspiring the pinhole photographers, it is the ability to build their camera themselves. Discovering a perfect lightproof box to the pinhole photographers is like finding a treasure. But in this section, I will take us step by step on how to construct a working pinhole camera.

Materials needed

A cardboard box

Masking tape

A scissors

Two camera films

A sharp knife

Step One

With the help of a sharp knife, carefully pop out one end of one of the film canister. On the successful opening of the canister, flip it upside down carefully so as not to spool the film and carefully place back the cap of the canister. This is to make the two films face each other enabling us to tape both light-sensitive parts of the film together. Now, carefully remove the spool from both films apply the masking tape on the reverse side of the film as shown above, the dotted lines shows the point where the two films where merged.

Step two

The pinhole camera as already stated is a camera without lenses, hence the job of letting light through the box is performed by the shutter, and hence to construct the shutter we cut out two sheets from the cardboard paper. On the first sheet, we make a square opening in the middle of the sheet and on the second sheet, we make a clean cut with a size slightly higher than the initial square opening. After this is done, we cut out a little rectangular sheet which can slide and fit into the second sheet as shown in the image above. This rectangular sheet is then placed between the two sheets and using the masking tape, we join the two sheets as shown above.

Step three

Here, we construct a light-proof box using the cardboard paper. Cut out a large chunk of paper and fold the cardboard into a box as shown in the image above. The dimensions of the box is very important at this point but I would recommend ensuring that the width of the box should be matched with the length of the shutter constructed above.

The masking tape should also be used to hold the loose ends of the fold in place and should be applied generously as no external light should be allowed to enter the box. I also recommend painting the edges of the box with black oil color to ensure no light enters the box. The opposite ends of the box are meant to be cut open as shown in the above image both cut made in the middle of both sides.

Step four

The opening provided on the box above is too large, hence to make a tiny perforation for the camera, we cut out a very small sheet from the cardboard paper and using a little needle, make a very tiny hole by rotating and pressing the needle downwards. After this, place the sheet on the smaller opening on the box as shown in the image above and using the masking tape, place the paper and ensure that the opening on the paper is at the center of the opening on the box. With this, our camera is almost ready for use!

Step five

Here, we combine the structures at step one and step four. At the opposite end of the box where the pinhole was placed, we carefully the light-sensitive film as shown in the image above. No need to fasten any of the structures with masking tape as this would be placed carefully in a box we would construct in the preceding step.

Step six

Taking note of the dimensions of the resulting structure in step five, we construct a box which will contain both the lightproof box and the light-sensitive film. Begin by cutting out a large cardboard paper and tracing out the dimensions on the cutout cardboard. Also, ensure to make two perforations at the appropriate position corresponding to the positions of the projecting end of both film canisters as shown above. Also, fold the cardboard as shown in the image above. Make perforations corresponding to the position of the aperture in the lightproof box as shown in the image above.

Step seven

At this point, we carefully place the structure resulting from step five above ensuring that the perforation of the containing box made in step six matches the perforation of the lightproof box. With this, your camera is rea, y for use and we can capture images by raising the shutter and placing it back at the point of taking pictures.

Also advance the film whenever you want to raise the shutter to take another picture. This can be done by carefully rotating both film clockwise or anticlockwise depending on the manner in which you placed the joined film in step one.

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Reference

1. Pinhole camera -wikipedia
2. Fisheye lens -wikipedia
3. What is distortion -photographylife
4. How a pinhole camera works -alternativephotography
5. Depth of field -wikipedia
6. Rectilinear propagation of light -tutorvista

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