Since the iPhone camera has a fixed lens opening, what two main camera settings do you adjust to change how bright or dark your photo looks?

The two main camera settings you adjust to change how bright or dark your photo looks, given a fixed lens opening, are Shutter Speed and ISO. Each setting independently controls the amount of light recorded by the camera sensor.

Shutter Speed dictates the duration for which the camera's sensor is exposed to light. It is measured in fractions of a second, such as 1/1000s, 1/60s, or even several full seconds. A longer shutter speed allows the sensor to collect light for a greater period, which brightens the resulting image. Conversely, a shorter shutter speed limits the time light hits the sensor, producing a darker image. An important side effect of adjusting shutter speed is its impact on motion: longer shutter speeds can introduce motion blur if the subject moves or the camera shakes during the exposure, while shorter shutter speeds effectively freeze motion.

ISO represents the camera sensor's sensitivity to light. A higher ISO setting increases the sensor's sensitivity, meaning it requires less light to produce a bright image, making it suitable for dim conditions. A lower ISO setting decreases sensitivity, requiring more light and resulting in a darker image. The primary trade-off associated with increasing ISO is the introduction of digital noise, which manifests as graininess or speckles in the image, thereby reducing overall image quality. A lower ISO generally produces a cleaner image with less noise.