Ambient light is somewhat uncontrollable and can be fleeting. Catching it may be a matter of preparation plus luck; of being ready while in the right place at the right time.
While touring a relative’s newly constructed home, I entered this unfinished bedroom on an overcast winter morning when the sky opened up for a few seconds. Incoming sunlight filled the room, bouncing off the wooden floor and illuminating the bed frame. I was able to squeeze off two frames before the sun disappeared behind the clouds.
Before entering the room my camera settings were adjusted for taking pictures in a dimly lit house. The aperture was set at f5.6 (a medium lens opening) with a shutter speed of 1/60 of a second (a slightly longer exposure time). When working with black & white film the desired result is to bring out the shadow detail so I didn’t change the aperture setting for this exposure. Adjusting the aperture would have underexposed the room details.
The camera, a Canon F1, was equipped with a manual focus adjustable lens that allowed me to bring the subject into focus while looking through the viewfinder. With the bright light coming through the window, I was able to quickly focus on the headboard.