How can you choose the perfect ISO for your 35mm film?

1 What is ISO?

ISO stands for International Standards Organization, and it's a numerical scale that indicates how fast your film reacts to light. The higher the ISO number, the more sensitive your film is, and the less light you need to make a proper exposure. However, higher ISO also means more grain, which is the visible speckles or noise that appear on your photos. Lower ISO numbers mean less sensitivity and more light required, but also finer grain and smoother images.

2 How to read ISO ratings

Most 35mm films have an ISO rating printed on the box and the film canister. Some films have a single ISO rating, such as 100, 200, or 400, while others have a range, such as 100-400 or 400-1600. A single ISO rating means that the film is designed to be exposed at that specific speed, while a range means that the film can be exposed at different speeds within that range. The range gives you more flexibility and allows you to adjust the exposure depending on the lighting conditions and the effect you want to achieve.

3 How to choose ISO for different lighting conditions

One of the main factors that influence your choice of ISO is the amount and quality of light available. Generally, you want to use lower ISO films for bright and sunny situations, such as outdoors on a clear day, and higher ISO films for low-light and indoor situations, such as at night or in a dimly lit room. For example, you might use ISO 100 or 200 for a sunny landscape, ISO 400 or 800 for a cloudy or overcast day, and ISO 1600 or 3200 for a dark or indoor scene. However, these are not strict rules, and you can experiment with different ISOs to create different effects.

4 How to choose ISO for different subjects

Another factor that affects your choice of ISO is the subject and the movement of your scene. If you want to capture sharp and detailed images of a still or slow-moving subject, you can use lower ISO films and a slower shutter speed. However, if you want to freeze the action of a fast-moving subject, such as a sports event or a wildlife scene, you need to use higher ISO films and a faster shutter speed. For example, you might use ISO 100 or 200 for a portrait or a still life, ISO 400 or 800 for a street scene or a landscape with some movement, and ISO 1600 or 3200 for a concert or a sports game.

5 How to choose ISO for different creative effects

The final factor that influences your choice of ISO is the creative effect and the mood you want to convey with your photos. ISO not only affects the exposure and the grain of your images, but also the contrast and the color saturation. Lower ISO films tend to produce more natural and realistic colors, while higher ISO films tend to produce more vivid and saturated colors. Lower ISO films also tend to have more dynamic range and smoother tonal transitions, while higher ISO films tend to have more contrast and sharper edges. For example, you might use ISO 100 or 200 for a soft and subtle look, ISO 400 or 800 for a balanced and versatile look, and ISO 1600 or 3200 for a dramatic and gritty look.

6 How to test different ISOs

The best way to find out how different ISOs affect your photos is to test them yourself. You can either use different rolls of film with different ISO ratings, or use a single roll of film with a variable ISO range and change the exposure settings accordingly. You can also use a light meter or a camera with a built-in meter to measure the light and calculate the correct exposure for each ISO. Alternatively, you can use a technique called bracketing, which means taking several shots of the same scene with different exposure settings, and then compare the results. By testing different ISOs, you can discover how they affect the brightness, the grain, the contrast, and the color of your photos, and choose the one that suits your vision and style.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?