Opening up refers to increasing the size of a cameras lens aperture or decreasing the shutter speed to allow more light to reach the film or sensor. This adjustment brightens the exposure, making it useful in low-light conditions or when a faster shutter speed is not critical.
Photographers often "open up" the lens to achieve a shallower depth of field, isolate subjects from the background, or capture better detail in dim environments. Understanding how to open up effectively is essential for controlling exposure, creative effects, and image quality in both digital and film photography.