Camera, Lenses, and Exposure
What this domain tests
Camera, Lenses, and Exposure asks you to control and explain the physical variables that create an image: how much light reaches the sensor, how the lens renders space, and how focus and motion are managed. Expect calculation-style items and practical judgment calls.
Core rules
- Exposure is a three-way trade: aperture, shutter speed, and ISO. One stop doubles or halves light at the sensor. Standard full-stop apertures run f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16; shutter speeds run 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30; ISO 100, 200, 400, 800.
- Equivalent exposures keep image brightness constant while changing depth of field, motion rendering, or noise.
- Depth of field increases with smaller aperture, greater subject distance, and shorter focal length. It decreases with closer focus and longer lenses. Sensor size changes the acceptable circle of confusion and therefore apparent depth of field at the same framing and aperture.
- Perspective is set by camera position, not focal length. Moving closer widens apparent relationships; a longer lens used from farther away compresses them.
- Diffraction softens detail as apertures become very small; every lens has a practical sweet spot.
Worked example
Start at f/8, 1/250 s, ISO 200. You want f/4 for shallower depth of field. Opening from f/8 to f/5.6 is +1 stop, and f/5.6 to f/4 is another +1 stop, so you have added two stops. To keep the same brightness, subtract two stops with shutter speed: 1/250 to 1/500 is -1, and 1/500 to 1/1000 is -2. The equivalent exposure is f/4 at 1/1000 s, ISO 200.
Traps that cost marks
- Reading the f-number sequence backward: f/4 is a wider aperture than f/8.
- Assuming crop factor changes exposure; it changes framing and apparent depth of field, not light per area.
- Using shutter speed to control flash exposure; flash is controlled by aperture, power, and distance within sync limits.
- Blaming lens softness when the real cause is diffraction, missed focus, or camera shake.