Which method increases the risk of overexposure when using different film speeds?

Choosing the wrong ISO for the lighting conditions can lead to overexposure primarily because ISO determines the film or sensor's sensitivity to light. When you set an ISO that does not match the light levels present in a scene, the resulting exposure can be too bright.

For instance, if you are in a bright environment and set a low ISO, the sensor is less sensitive, which may require a longer exposure time to achieve a correctly exposed image. Conversely, if you set a high ISO in low light, the sensor may become overly sensitive and capture too much light, leading to overexposure.

This issue can be compounded in situations where light levels change frequently or are misjudged, emphasizing the importance of selecting the correct ISO to align with the shooting conditions.

While using ambient light, a larger aperture, and decreasing shutter speed can all influence exposure, they do not directly carry the same risk of consistently resulting in overexposure if the ISO is set correctly for the environment. Each of these techniques can be managed effectively with adjustments in other settings to maintain the desired exposure without the inherent risk associated with improper ISO choices.