Pinhole Photography

I have been intrigued by ‘pinhole’ photography since my 1960’s Art College days. But more recently by Tom’s work in this area. Unlike Tom, I just use my normal digital mirrorless camera, and mount a ‘pinhole’ on the front.

Pinhole photography is one of the simplest and most fascinating forms of photography. Unlike modern cameras, which use complex lenses and electronic sensors, a pinhole camera can be made from a simple box or container with a tiny hole in one side. Despite its simplicity, it can produce real photographs and demonstrates the basic principles of how light and images work.

A pinhole camera works because light travels in straight lines. When light passes through the tiny hole, rays from different parts of the scene cross through the opening and form an inverted image on the opposite side of the camera. The image can be captured on the digital sensor. Because there is no lens to focus the light, the tiny hole itself acts as the camera’s aperture.

One of the most interesting features of pinhole photography is its unusual appearance. Pinhole photographs have a soft, dreamlike quality because the image does not have the sharpness produced by a conventional lens - the images are VERY unsharp - though some people describe as ‘unclear’ or ‘ethereal’. The photographs can also have a very deep depth of field, meaning that objects at different distances can appear reasonably clear. Long exposure times are normally required because only a small amount of light enters through the tiny pinhole.

Creating a pinhole camera can be an enjoyable practical experiment. A basic camera can be made using a lightproof box, a piece of aluminium foil and a needle. A very small, clean hole is made in the foil and attached over an opening in the box. The inside of the box must be dark enough to prevent unwanted light from reaching the photographic material. Once the camera is pointed at a subject, the pinhole is uncovered for a carefully measured (guessed) period before being closed again. This often involves film as the recording medium, which can be very frustrating, awaiting development before seeing if the exposure is reasonably correct.

Whilst a good, modern digital camera - especially a mirrorless SLR - should be able to manage exposure automatically, often exposure compensation is required, as the pinhole lens ‘aperture’ falls outside the effective range the camera is designed for.

A smaller hole can produce a sharper image, but it also allows less light into the camera, increasing the required exposure time. It also increases diffraction, softening the image and producing colour fringing. A larger hole allows more light in but may result in a less defined image. Nothing is ‘specific’ in pinhole photography, except the enjoyment.

For a simple pinhole lens, the hole should be very small—around 0.2–0.5 mm in diameter.

A good starting point is about 0.3 mm. You can make it by gently pushing a very fine sewing needle through thin aluminium foil - use only the ‘thinnest’ part of the needle.

    Smaller hole: sharper image, but needs a longer exposure.

    Larger hole: brighter image, but more blurred.

    Too small: diffraction can make the image blurry again.

I created a pinhole lens for my Sony by buying from eBay a very thin steel sheet with a 0.35mm hole in (my attempts at punching my own all created holes greater than 1mm, and the aluminium foil was too crumply to handle). A 6mm hole was drilled in a spare body cap, and the thin sheet glued onto it so the tiny pinhole was centred on the 6mm hole. I tried to ‘neaten up’ with black tape.

Technically this worked, though I often had to dial in exposure compensation up to +/- 2stops in the camera. I liked the effect. BUT the images were/are VERY unsharp.

So I bought a commercial pinhole ‘lens’ for my Sony, also from eBay - a thingyfy Pinhole Pro S wide-angle pinhole lens. Very well engineered from a single aviation aluminium block. Supposedly having an 0.14mm diameter hole/aperture - though it doesn’t look any smaller to me than the above plate. But they are so small you cannot measure. And, of course, unfortunately the images are also VERY unsharp.

All exposures, via both lenses, are longer than 1/10S, at ISO640; so a tripod is always necessary. ISO could raised into the thousands, but one effect is further reduced sharpness, so this is not recommended. I will be moving down to ISO100. A further problem is the ‘lens’ is a hole; and it lets a fair amount of dust onto the sensor. Cleaning is required after every session.

Tom’s images are much sharper… a classic case of optical physics. Using the same sized ‘holes’ if the ‘sensor’ (film) is larger the images will be apparently sharper (less enlargement). But I wish to stick with ‘35mm’ (full frame) image size.

In practice, restricting subjects to contrasty ones, on a bright sunny day, adding oodles of clarity and sharpness can make an image ‘acceptable’ - just.

Which leaves me in a bit of a quandary … will I continue to use, where, on what subjects?

The answer is… I’m hooked; so ordered the Zero Image classic dual 35mm film pinhole camera, which fits in with my long standing love of digitising mono 35mm film. But that’s for another blog…

For the TechnoPhobes

For a typical homemade pinhole lens, 0.3 mm is a good starting size (it is the usual ‘circle of confusion’ quoted in sharpness discussions.

The ‘effective aperture’ depends on the distance from the pinhole to the sensor (the pinhole-to-sensor distance - effectively the focal length - which means you can insert extension tubes to make ‘longer’ lenses, though this reduces the effective aperture even more).

The relationship is: F = \frac{l}{d} where:

     F= f-number

     l = pinhole-to-sensor distance

    d = pinhole diameter = 0.3 mm (eg)

Thus:

Pinhole-to-sensor distance (l) Effective f-number

10 mm f/33

20 mm f/67

24 mm f/80

35 mm f/117

50 mm f/167

100 mm f/333

So, if a 0.3 mm pinhole is 24 mm from the full-frame sensor, it behaves approximately like f/80 in terms of geometric aperture.

In my case the home made hole is about 27mm from my sensor, so approx f100;

The thingyfy hole is about 20mm from the sensor plane, so IF it was a 0.3mm hole it would be about f67… but as (supposedly) much smaller, more like f150.