Halation in Film Photography, Explained

Film is an imperfect, physical medium.

Some of the smartest minds have been refining it for nearly two hundred years, yet it continues to surprise us with its random, organic artifacts to this day.

Before the introduction and proliferation of digital photography, many resources were aimed at minimizing the grain, improving clarity, and fine-tuning the colour science. Today, some of the best-known emulsions continue the tradition of technological innovation for more image and less noise.

But in the post-perfectionist world, where clinical image accuracy is relatively easy to achieve, film artifacts are now valued for their expressive potential and unique, one-of-one renderings of the real world. Halation is one such artifact, which I will explain and discuss at length in this mini-guide.

In this guide: What is halation? What causes halation? It’s not the pressure plate that causes halation. How anti-halation layers work. Which films can produce halations? Halation vs. lens bloom vs. haze. A creative effect. Support this blog & get premium features with GOLD memberships!

What is halation?

Halation in photography is an effect that manifests as white, red, or orange halos around bright points of light in a photograph caused by rays reflecting and scattering around the film layers furthest from the lens.

Colour film is structured in a way that the red-sensitive layer is the farthest from the lens, where the halation effect usually forms. This is why colour film would typically render red halos.

Halation may occur in all types of film, including black-and-white, which renders the halation in white. However, it is usually minimized using various anti-halation technologies.

Halation in colour film may also add a red tint to the bright areas of an image. For example, your overcast skies may look a little pink.

What causes halation?

Photographic film is very thin and flexible, but it’s made of several even thinner layers. As the light travels through those layers, it reaches the border between the film base and air, where some of the light is reflected back.

This phenomenon is known as total internal reflection. You may’ve witnessed it when looking at a mirror-like air surface while looking up from below submerged in a pool. Total internal reflection is the result of light rays reflecting back at an oblique angle when reaching the boundary to the less dense medium (i.e., water-to-air).

Like the reflections off the water-to-air boundary when you look up during a dive, the light travelling through photographic film can reflect off the boundary between the emulsion medium and air.

As the light reflects from that boundary, it saturates the first photosensitive layer (in colour film, it usually happens to be red), forming a halo around the entry point — see the illustration above.

It’s not the pressure plate that causes halation.

The majority of online resources claim that halations are caused by the light bouncing off a camera’s pressure plate. But that made little sense to me, and a Kodak-trained and certified film process technician I spoke to on Threads.

Film pressure plates (pieces of metal mounted on a film door that push against film to keep it flat when the camera is closed) are usually coated in black paint. While that paint will not guarantee total light absorption, it’s likely no less absorbent than the anti-halation layers within film.

The air gap between the film and the camera’s pressure plate, however small, is inevitable, resulting in total internal reflection (TIR). Which is why anti-halation layers are built as integral components — no air, no TIR!