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Questions and Answers
What is the primary function of the iris in a camera?
What is the term for the ratio of focal length to aperture diameter?
What is the effect of increasing the f/ number?
What is required to achieve a deep field of focus?
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What happens to the iris area when the f/ number increases by one stop?
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What is the effect of closing the iris?
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What is the term for the distance over which objects appear to be in focus?
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What is necessary to obtain the same illumination when the aperture is reduced?
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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.
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Description
Understand the components of a camera, including lens, iris, shutter, and sensor. Learn about focusing a camera and the concept of depth of field.
