Wednesday, February 06, 2013

About Pinhole Photography


I sometimes get interesting feedback, usually after someone’s asked me what I’m doing this weekend and I’ve replied that I’m going to do some pinhole photography. It’s typically one of two responses, either “Oh, I used to do that as a kid,” or “Pinhole photography, what’s that?”

It’s not like I’ve actually done any pinhole photography lately, however. I think the last time was mid-2012. There was a time, maybe five years ago, when the majority of my spare creative time was spent either building pinhole cameras or making images with them. And then my photographic interests continued to expand to include digital image-capture, roll-film cameras and large format lens-based photography. Too many irons in the fire, perhaps?

What brought this to mind was, over on F295’s pinhole photography discussion forum, a long-time member had commented that they missed my once-regular paper negative pinhole landscape images. I’ve found that, over the years, what motivates me is often the desire for recognition by other peers in the field, of which online specialty discussion forums, like F295, are invaluable for cultivating a creative subculture and providing encouragement to the otherwise lone practitioner. This kind of encouragement is just what I need to get back in the game.

So, just what is pinhole photography, you might ask? It’s simultaneously simple and complex.


There is no simpler type of photography than pinhole. Just a light-tight enclosure (“camera” in Latin means room or chamber) with a light-sensitive surface in one side (film, photo paper or a digital sensor) and a tiny aperture in the other, through which light is projected to form a recordable image. Really, that’s all any camera actually is, in essential functionality, after you’ve removed all the bells and whistles.

Many people consider the simplest form of photography to be the most convenient, like pulling out your cell phone and instantly capturing some scene that can be, within seconds, uploaded to one’s breathlessly awaiting public. Convenient and expedient, yes; simple, no. For all of the complexity that makes digital photography convenient is hidden away inside tiny silicon microchips, out of sight as well as mind. The complexity of the process is concealed from the user, obscured by a false-front of artificially-contrived mediation.

With the pinhole technique, conversely, there is little mediation in the process, but rather a direct connection between the objective reality being depicted and the subjective representation being created. All of it, from the making of the camera, to the fine-tuning of the process, to the development and printing are all hands-on-intensive activities that require an exacting focus upon the materials and methods, and an investment of time, but which in turn reward the practitioner immeasurably.

The most essential question about pinhole photography is how a mere hole can form an image at all. For me, this is one of the most mysterious and yet satisfying parts of the entire process, for it gets down to the essential properties of light itself, its dual nature that’s simultaneously particle- and wave-like.


I’m not a quantum physicist; neither is an education in optics a prerequisite for creating great pinhole images. But I’ve found that a basic description of the principles, though technically simplistic, will suffice to serve as a layman’s explanation.

The basic reason a pinhole casts a coherent optical image has to do with projection. Light reflects off every point of an object’s surface in multiple directions and angles, like small particles traveling in numerous straight lines, but an extremely small hole only permits a narrow range of perspectives to pass through the pinhole aperture onto our film plane inside the camera. How small of a hole, and its uniformity and thinness, affects the quality of the image projected.

Conversely, think instead of a large hole in our camera, too large to form a sharp image. Objects will appear fuzzy in our picture because a wide variety of images, each from slightly different angles, are all simultaneously being projected in an overlapping blur. But as we decrease the size of the hole, the image gets sharper because the range of various overlapping images is reduced. If we were to further reduce our pinhole’s diameter to almost infinitely small, we could imagine images nearly as sharp as a glass-lensed camera. But we can’t, because other factors come into play.

Light, like all wave phenomena, has this curious property of bending around edges and corners. The cone of light passing through our pinhole aperture has a part of it that is near enough to the edge of the hole so as to be bent, which is called diffraction. The amount of diffraction has to do with how much of the light passes near enough (within a wavelength or so) to the edge, as compared to the rest of the light bundle that passes more through the middle of the pinhole aperture, missing the edge entirely. If we start with a large-diameter hole, a majority of its light bundle entirely misses the edge, with only a small fraction passing near enough to cause a tiny bit of diffraction in the image. But as the size of the pinhole is decreased, the perimeter area of the hole that causes diffraction begins to dominate over the central area that’s unaffected. Make the hole small enough and virtually all of the light passing through comes close enough to the edge to be diffracted.


You may by now notice that there are these two competing principles at work to affect the sharpness of our pinhole picture: projection and diffraction. Projection has to do with the particle-like property of light and is affected by the size of the hole and the distance from the hole to the film, with the smaller aperture producing a sharper projected image, while diffraction has to do with the wave-like property of light and is affected by the wavelength of light and the size of the pinhole, with the smaller aperture producing more diffraction, tending to soften the image.

If you were to graph both of these phenomena together, you’d see that where the two curves cross is a point of optimal system sharpness, representing the best compromise between diffraction effects and projection effects, accounting for both the wave-like and particle-like dualities of light, and that for any given focal length of camera and wavelength of light there is one optimally sized pinhole.

Of course, you don’t have to bother with all of this talk about photons and diffraction effects to make great, compelling images, unless a somewhat sharp image is important to the kind of pictures you create. Many great pinhole images are created with little concern for optimizing the camera’s pinhole size. But there are many of us in the world of pinhole photography to whom crafting a finely-tuned pinhole camera, one that makes compellingly sharp images, represents an irresistible challenge.

However, there are other parameters in the picture-making process that can induce negative consequences onto the overall image quality besides pinhole size. Shutter speed is one such parameter. Even with fast photographic films, exposure times can often be on the order of a minute or more, meaning that any slight movement of the camera can blur the image from its optimal sharpness. Even atop a sturdy tripod, soft ground can cause the tripod legs to settle over time, or wind gusts can vibrate the camera sufficiently to cause motion-induced blur. And the larger the camera the bigger the problem, which is one reason why there appears to be an upper practical limit on format size in real-world conditions.


Relating to exposure, I like to think of pinhole photography using another analogy, that of the garden hose and bucket. Let’s say you have a bucket which you need to fill up. The bucket is your image, the size of the bucket being how much visual information is present in the image. You have to fill up the bucket using a garden hose. The size of the hose is your pinhole aperture and the time required to fill the bucket is your shutter speed. The total volume of water used is your overall exposure, while the pressure of the water in the garden hose is the brightness of the scene being photographed.

You can use fast-speed film, which is represented by a small bucket. It doesn’t take as long to fill up, because its volume is small, but it contains less visual information. A larger bucket, represented by slower film, contains more information, but takes longer to fill up.

There’s a third factor in this garden hose analogy, which is evaporation. If your bucket is too large and your garden hose too skinny, it takes the bucket so long to fill up that, while it’s filling, some of the water is evaporating out of it, meaning you have to add some additional exposure time to account for the difference. In photography, we call this “reciprocity failure,” and happens more so with film and less so with photo paper.

One of the temptations, after getting obsessed with pinhole photography, is to want to make the largest, sharpest pinhole camera possible. But there are practical limits to how far you can successfully take this and get meaningful improvements.


Because the exposure we give to the light sensitive media inside the camera is related to the area of our pinhole aperture and the time the aperture is open, a larger sized camera format, optimized for sharpness will, with its larger surface area, require a longer exposure time, all else being equal.

Knowing that there’s an upper limit to how fast we can record an image in a pinhole camera, the larger film format gives more chance for the tripod to shift position or the camera to vibrate in the wind, further reducing the information throughput of the system. The larger, heavier camera also requires a steadier tripod, adding even more weight. For this reason, it becomes necessary to define a practical upper limit to how big of a film format you wish to employ, striking a fine balance between quality and practicality. For cameras that employ sheets of film or photo paper, that are subsequently either scanned or contact printed for output, I’ve found a practical balance to be in the 5”x7” format or thereabouts, with an upper limit around the 8”x10” size.

But for other people, portability and practicality trump overall image quality, a lesson I’ve had to learn the hard way, of which I’m reminded of the time that my wife and I hiked up to the top of Delicate Arch, in Arches National Park, during the middle of a Utah summer, she lugging the heavy Bogen tripod and I the large 8”x10” box camera, backpack and changing bag. An exercise in pinhole extremism, for sure. Though the pictures were satisfactory, I’m doubtful they were any better than if I’d been employing a carefully optimized camera of a smaller sized format, because of the wind atop Delicate Arch that day.

Conversely, I’m reminded of what operating near the lower limit of the format-size spectrum is like, when I read of people being disappointed by the results from attaching a pinhole aperture to their digital SLR camera, the problem being that, even in the case of a so-called “full-frame” camera, a 24mm by 36mm image area is pretty small and, for a normal angle of view, the focal length so short that the optimal focal ratio (the ratio of focal length divided by pinhole diameter) amounts to barely over f/100. Compare this to a 5”x7” format pinhole box camera whose optimal focal ratio is around f/300, resulting in a sharper image that’s also much larger.

There’s much more to write about regarding pinhole photography and too little space or time for you to comfortably digest, so perhaps I’ll post more at a later date. In the meantime, this lengthy essay serves not only as motivation for you to begin your own journey in pinhole photography, but is really just further reason for me to get outside in the near future, to somewhere scenic, with a box camera and paper negatives (or that newly-purchased Holga and some 120-format color film) and create some new images myself. Which, if I do, I’ll be sure to share with you the results.

Post-Script: I wrote this piece last week and worked on revisions earlier this week, using iAWriter on the iPad2, but had sent the roll of Kodak Ektar 100 film to the lab in the mean time, shot on my Holga 120 format pinhole camera. I was pleased enough with the results to include some images herein, scans of luster-finish prints. The camera was tripod mounted for all of these images, exposure times being around 3 seconds each.


Blogger Rob Bowker said...

Thanks for the insight Joe. Funny how you (one) sort of know how how it works but don't realise there's a bit more science behind it than you first thought. The explanation of the relation between refraction and hole size was a revelation. I'm not sure I'll be making any pinhole images very soon, but it all informs the art and practice of photography - so thanks.

4:27 AM  
Anonymous George Sheils said...

I just clicked through to your blog from f295 today. I've got to say you have a fine way of clearly expressing what pinhole photography is all about. This would be invaluable for anyone wishing to know how and more impoiortantly why they should go about making ensless images.
I enjoyed reading it, immensely.


7:50 AM  

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