How to Measure the Dynamic Range of Film

You Can (Sort-Of) Do It at Home

7 min read by Dmitri.
Published on October 10, 2023. Updated on July 4, 2024.

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Figure 1. Scanning the light falloff on a sheet of paper with a light meter and marking each decreased stop of metered exposure.

In this guide: How manufacturers measure their films’ dynamic range. How to measure your film’s dynamic range and plot film characteristic curves at home. Support this blog & get premium features with GOLD memberships!

Understanding the dynamic range of your emulsion can help you make better images¹.

It will inform you how your film will behave in various lighting conditions in a way no sample photo or a description lacking this information can. I base most of my exposure recommendations in my film reviews on dynamic range data, and this guide on making perfect exposures revolves around it too.

Some photographers even rely on dynamic range data to identify the source of the rebranded film stocks. Unfortunately, not all manufacturers list this information, which is a shame as it would’ve helped us make better images¹ with films such as Polaroid, Instax, Film Ferrania P30, and many others.

In this short guide, I will explain how film’s dynamic range is measured by the manufacturer and how you can even estimate the dynamic range at home with simple tools like a sheet of paper and a light source. This is the exact method I used to graph my Polaroid film characteristic curves.

If you aren’t familiar with the concept, I wrote a guide that explains dynamic range in simple terms. TL;DR: dynamic range is a number that describes how much of the shadow and highlight information a particular film can register simultaneously. This single number is taken from a graph of film densities (how dark/light the developed film emulsion is) in response to set light intensities — called film characteristic curves.

If you are still unsure what dynamic range is or how film characteristic curves may be helpful to your photography, this article may help you understand these concepts in practical terms.

¹ — It’s understood that “better” or “best” are subjective terms; however, in this context, they mean getting results you envision with less guesswork and fewer film frames wasted.

How manufacturers measure their films’ dynamic range.

Film negatives look darker when they receive more light and lighter/more transparent when they get less. Film’s dynamic range is the range of brightnesses of the received light between the darkest and the lightest shade the emulsion can produce — which are graphed as characteristic curves (see the illustration below).

A hypothetical negative film characteristic curve.

Given how convoluted the concepts of dynamic range and film characteristic curves may seem, measuring and graphing them is quite simple; it generally involves just three steps:

1) A large sheet of film is laid out in the dark, and a board with gels of varying densities is laid on top. The first gel will cut the light by one stop, second by two, third by three, etc. An exposure is made for a known amount of time by a light source of a known light intensity. The film is then developed.

1a) The manufacturer may repeat this experiment with varying developing methods if they believe they will affect the film’s response significantly. If it’s a colour film, the gels will be coloured to correspond with each of the layer’s dyes (i.e., red, green, and blue).

2) The result is a piece of film with bands of increasing darkness created by the gel filters. The manufacturer will then use a densitometer to give them a value in D-units for each band.

3) The densitometer values are plotted on the Y-axis of a graph against the lux-seconds (known amounts of light that pass through each gel filter stage) to create a film characteristic curve. Colour films will have three curves plotted on the same graph for each channel.

Film characteristic curve for Ilford FP+ developed in ILFORD ILFOTEC HC (1+31) for 8 minutes at 20°C/68°F with intermittent agitation.

The resulting graph shows how well the film responds to different light intensities. You’ll notice that in the middle, it slopes nicely in a straight line, but at each end, it curves into a flat line — which is where adding more light can not make the negative any darker or subtracting more light can not make the negative any more transparent. These are the limits of the film’s sensitivity, and the range between them (X-axis) is the dynamic range.

✪ Note 1: Manufacturers predominantly use lux-seconds (log exposure) on the X-axis of the film characteristic curves to inform the varying light intensities the film has been exposed to during the tests. Lux-seconds can be easily converted to stops using a free app on this website.

✪ Note 2: This chapter explains one of the simplified methods of measuring film properties. There are other ways of doing this.

As a photographer, you can then estimate the range of stops between the darkest and lightest parts of your scene and match that against the dynamic range of the film to see how well it will capture what you see. You can also examine the curves and understand how the film will react to under- and over-exposures based on the shape of the curve; if the curve turns horizontal gradually, the transition will be soft (and vice-versa).

There are many more useful pieces of information you can get from those graphs, but for the sake of brevity, I’ll move on to the final chapter:

How to measure your film’s dynamic range and plot film characteristic curves at home.

I have neither a densitometer nor a calibrated light source; no gels are lying around my house. But a blank sheet of paper, a free light meter app, a lamp, a blackout light curtain, and a scanner are all that’s needed to make “good enough” estimates.

Polaroid film is notoriously difficult to shoot as it tends to simultaneously under- and over-expose — a sure sign of a low dynamic range. But to understand exactly how it reacts to light, I wanted to read its film characteristic curves; alas, Polaroid does not publish them, so the next best thing would be to make some.

Here’s how I did it and how you can do it, too:

1) Set up a lamp in a dark room to shine onto a piece of paper in a way that creates a soft gradient.

2) Use a light meter to scan the sheet from the brightest to the darkest spot and mark each time it returns a change in measurements of a full stop. See Figure 1 at the top of the article. Note that you may need a long sheet of paper to measure films of more than five stops of dynamic range; thankfully, Polaroid films are less than that.

3) Set up your camera and make a few exposures of your sheet with markings; you can meter for the middle of your sheet, but I suggest you bracket a few exposures. See Figure 2.

Figure 3. Measuring the RGB values around the markings of a scanned test image. It’s best to take a few measurements and average the result.

4) Scan the results and then use Adobe Photoshop or any image editing software capable of measuring pixel values around your markings. Make a few measurements from your best scan and average them; be careful not to include the actual marks in your measurements (just the white paper bit). If you’re measuring colour film, record all three channels (R, G, B); convert the image to monochrome for black-and-white film.

5) Plot your values in your favourite spreadsheet app (Excel, Numbers, Google Sheets, etc.) Use your pixel values (0-255) for the Y-axis and the stops that you used in your markings for the X-axis (it doesn’t matter which number you start from). Then, use your app to generate your graph.

Polaroid 600 Color film characteristic curve.

Obviously, this method is not as accurate as something that’s done at a lab with appropriate tools. There are many reasons why: the camera’s lens flaring can skew the results, uneven and imbalanced colour temperature lighting, and the imprecise nature of equating film density to RGB value readouts.

Still, I found the results useful. At the very least, this exercise may help you understand the dynamic range and film characteristic curves better.

You can download the graphs I made from a variety of Polaroid films and the summary of the steps to create them here:

➜ Free Download: Polaroid Film Characteristic Curves (PDF)

If you tried this method, let me know how it goes — or feel free to ask any questions you may have about this technique and add any suggestions/corrections in the comments below. 👋

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How manufacturers measure their films’ dynamic range.

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Dmitri