Camera Anatomy and Focus

Camera Anatomy

• A camera consists of a lens, iris (aperture), shutter, and film/sensor.
• Mirrorless digital cameras use an electronic shutter instead of a traditional mechanical shutter.

Focusing a Camera

• The lens-film distance must increase until it equals the image distance for the lens' focal length and object position.

Depth of Field

• Depth of Field (DoF) is the span of distance that can be in focus.
• Small distance changes in normal situations allow distant and nearby objects to be in focus simultaneously.
• Blur is caused by marginal rays, which can be removed by closing the iris (aperture).

Aperture and Shutter Speed

• The f/ number expresses the ratio of focal length to aperture diameter.
• A smaller aperture means a larger f/ number (for a given fixed focal length).
• For each jump in f/ number, the iris area changes by a factor of 2.
• Shutter speed describes the fraction of a second the shutter is open (e.g., 1/n sec).
• For each jump in shutter speed, the time open changes by a factor of 2.

Light Density on Sensor

• Light density on the sensor = Illumination x (shutter open time) / (f/ number)^2.
• Constant illumination requires compensating for changes in f/ with changes in shutter speed.

Deep and Shallow Fields

• Deep field: Requires high f/ number + more lighting or longer exposure.
• Shallow field: Requires small f/ number + reduced lighting or shorter exposure.