What is ISO, ASA and Film Speed ​​in Film Photography?

The terms ISO (International Standards Organization), ASA (American Standards Association), and film speed all refer to the same characteristic: the film's sensitivity to light. In film photography, the higher the ISO number, the more sensitive the film is to light. This means you can capture images in low light conditions with shorter exposure times. Conversely, a lower ISO indicates a lower sensitivity, which is ideal for bright light conditions, such as a sunny day.

Understanding how to use these settings to achieve the best possible exposure for the lighting conditions is essential for any film photographer.

ISO and ASA: Differences and History

Historically, ASA was the standard used primarily in the United States to indicate film speed. The term ISO took over with international standardization, unifying measurement systems under a single standard, making it easier to compare films of different brands and origins. However, the two terms are often used interchangeably in the context of film photography. When you see "ASA" on a film camera, it is simply the same measurement as ISO used today.

This unification simplified film selection for photographers and allowed for greater consistency in film photography, whether you were using a classic camera or a modern 35mm camera.

How does ISO sensitivity work on a film camera?

The ISO on a film camera is an indication of how quickly the film reacts to light. On your camera, you set the ISO to match the ISO of your film. For example, if you're using Kodak Portra 400 film, you'll set your camera to ASA 400. This setting allows the camera to correctly calculate exposure based on the ambient light. Film cameras often have a small dial that you can turn to adjust the ISO. This setting also affects how the camera's light meter measures light and recommends aperture and shutter speed settings.

Differences between low, mid and high ISO films

Choosing the right ISO sensitivity based on your shooting conditions is crucial. Here's a more detailed guide to choosing the right photographic film based on your subject and shooting environment:

• Low ISO films (20-200) : Ideal for bright days or conditions where plenty of light is available, such as landscape or architectural photography. They produce an image with less grain and more fine detail, providing exceptional sharpness and depth. Low ISO films like Fuji Velvia 50 are also excellent for capturing vivid colors and intricate details.
• Mid-ISO films (ISO 400) : Offer a good compromise between speed and image quality, and can be used in a variety of lighting conditions. Films like Kodak Tri-X 400 are especially popular for their flexibility, whether shooting indoors or outdoors, in natural light or with flashes.
• High ISO films (800 and above) : Ideal for low light conditions or when you want to capture fast moving subjects, but at the cost of more grain. Films like Ilford Delta 3200 are popular for concert photography, nighttime street photography, or indoor sports photography. The grain produced by these films often adds an artistic texture, accentuating the mood of the scene being photographed.

Impact of ISO choice on image quality

Choosing the ISO not only affects the brightness of an image, but also its quality. The higher the ISO, the more visible grain in the image. This grain is due to the larger silver bromide crystals in the film emulsion, which are needed to capture more light. For example, an Ilford HP5 Plus 400 film will have more visible grain than an Ilford Pan F 50, but will still allow you to shoot in low light conditions without a tripod. Understanding how grain affects the final appearance of your images will help you choose the right film for the right project.

Examples of popular movies and their usage

To help you choose the perfect film for your needs, here are some examples of popular film stocks and their ideal applications:

• ISO 100 – Kodak Ektar 100 : Ideal for daylight landscapes and static subjects. This film is renowned for its rich colors and exceptional detail.
• ISO 400 – Kodak Portra 400 : A versatile choice for natural light portraits and urban scenes. It offers a very natural color balance and is very forgiving in terms of exposure latitude, making it a favorite among professional photographers.
• ISO 3200 – Kodak T-Max P3200 : Perfect for night photography and fast action scenes. This film offers excellent grain management despite its high sensitivity, making it very useful for low light shooting.

Pushing and pulling your film: Adjusting ISO sensitivity for more flexibility

Pushing or pulling film involves exposing a film at a different ISO than what is listed on the box, and then adjusting the development process to compensate. For example, if you expose an ISO 200 film at ISO 400, you need to "push" the development to match this overexposure. This can be useful for low-light scenes or for creative effects by playing with contrast and grain. "Pull" film, on the other hand, involves underexposing a film and reducing the development time, which can soften contrast and reduce grain.

Pro tip: Experimenting with push and pull can greatly impact the final result of your photos. This can be especially helpful for black and white, where grain and contrast play a crucial role in the aesthetic of the image. If you’re looking to achieve a more dramatic look or unique texture, these techniques are powerful tools in a film photographer’s arsenal.

How to Choose the Right ISO for Your Photography Needs?

Choosing an ISO depends on many factors such as lighting conditions, subject type, and desired aesthetic. For sunny days, opt for a low ISO film for sharp, detailed images. For versatile outdoor and indoor photography, an ISO of 400 is often the best choice. Finally, for nighttime or moving photos, a high ISO will give you the flexibility you need.

Remember that film photography is an invitation to experiment and learn from mistakes. Choosing the right ISO is a skill that improves with time and practice. Experiment with different films and techniques to see what works best for your style and subjects.