ASA, also known as the American Standards Association, was an organization that developed a system for measuring the sensitivity of photographic film to light. The ASA system was based on the film’s ability to capture light and produce an image. The lower the ASA rating, the less sensitive the film was to light, and the higher the rating, the more sensitive the film was to light. For example, a film with an ASA rating of 100 would be less sensitive to light than a film with an ASA rating of 400.

Over time, the ASA system became outdated, and the International Organization for Standardization (ISO) took over the responsibility of developing and maintaining a standard for measuring the sensitivity of both film and digital camera sensors. The ISO rating system is now commonly used by photographers to determine the sensitivity of their camera’s sensor or film.

The ISO rating system is based on a numeric value that indicates the camera’s sensitivity to light. The lower the ISO value, the less sensitive the camera is to light, and the higher the ISO value, the more sensitive the camera is to light. For example, an ISO rating of 100 would be less sensitive to light than an ISO rating of 800.

The ISO rating system is logarithmic, which means that each increment in ISO value doubles the camera’s sensitivity to light. So, an ISO rating of 200 is twice as sensitive to light as an ISO rating of 100, and an ISO rating of 800 is twice as sensitive as an ISO rating of 400.

A higher ISO rating allows photographers to take photos in low-light situations without requiring a longer exposure time or a wider aperture. However, higher ISO values can also introduce more noise or graininess into the image. Therefore, photographers often try to use the lowest ISO rating possible while still being able to capture the image they want.

In summary, ASA and ISO are two standards used in photography to measure the sensitivity of film or digital sensors to light. ASA was the original standard, developed by the American Standards Association, and ISO is the current standard, maintained by the International Organization for Standardization. The ISO rating system is based on a numeric value that indicates the camera’s sensitivity to light, with higher ISO values being more sensitive to light but potentially introducing more noise into the image.

In digital cameras, the base ISO setting is determined by the sensor’s hardware design and characteristics. The base ISO is the sensitivity level at which the sensor can capture the maximum dynamic range, signal-to-noise ratio, and color depth without introducing significant noise or other artifacts into the image.

When a photographer selects the base ISO setting, the camera sensor receives the optimal amount of light for each pixel, resulting in high-quality images with minimal noise or graininess. The base ISO is usually the default ISO setting for a camera, and it is often recommended by camera manufacturers and professional photographers as the best starting point for capturing images with the highest quality.

In addition to the base ISO, many cameras offer an extended or expanded ISO range. The extended ISO range allows the photographer to increase the camera’s sensitivity beyond the native or base ISO setting. However, the extended ISO range comes at a cost of increased noise or graininess in the image.

It is worth noting that not all cameras have the same base ISO setting. Different camera models and sensor designs have different base ISO values, which can range from ISO 50 to ISO 200. In some cameras, the base ISO setting can be changed in the camera’s settings menu, while in others, it is fixed.

In summary, the base ISO setting is determined by the camera sensor’s hardware design and is typically the lowest ISO value that can capture images with maximum dynamic range, signal-to-noise ratio, and color depth without significant noise or graininess. It is often the recommended starting point for photographers who want to achieve the best possible image quality in good lighting conditions.