8 Questions
What is the primary function of the iris in a camera?
To regulate the amount of light entering the camera
What is the term for the ratio of focal length to aperture diameter?
F/ number
What is the effect of increasing the f/ number?
The aperture diameter decreases
What is required to achieve a deep field of focus?
A high f/ number and more lighting or longer exposure
What happens to the iris area when the f/ number increases by one stop?
It halves
What is the effect of closing the iris?
Less light enters the camera
What is the term for the distance over which objects appear to be in focus?
Depth of field
What is necessary to obtain the same illumination when the aperture is reduced?
A brighter scene or a longer shutter opening time
Study Notes
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.
Understand the components of a camera, including lens, iris, shutter, and sensor. Learn about focusing a camera and the concept of depth of field.
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