Physics 25: 1-6 Optical Instruments
Text Reading: Giancoli, Physics - Principles with Applications, Chapter 25: Sections 1 to 6
- Section 1: Cameras focus light on a detector surface which may either be a film with a chemical coating that reacts to light, or a photosensitive electrical surface (charge-coupled device or CCD) that measure light wavelength and intensity. In digital cameras, these measurements are stored as codes for a given area of the picture (picture element or pixel).
- Section 2: The human eye focuses light through the cornea (primary area of focus) and the lens (fine adjustments). Failure to focus correctly can result in nearsightedness (objects focus in front of the retina, and far objects are out of focus), or farsightedness (objects focus behind the retina, and near objects are out of focus).
- Section 3: A magnifying glas uses a simple lens to enlarge the image reaching the human eye. Actual magnification must include the eye's location and focus.
- Section 4: Astronomical refracting telescopes use an eyepiece for fine focus and magnification adjustments, and a primary lens for magnification. Reflecting telescopes may incorporate a series of mirrors and lenses to increase focal length within a given physical telescope, or direct light to special detectors.
- Section 5: The compound microscope uses multiple lenses to drastically increase magnification of a near object.
- Section 6: Aberration is the deviation from a perfect focus. Spherical aberration occurs when non-parallel rays focus at different points, creating a circle of confusion or fuzzy image. Chromatic aberration occurs when light of different wavelengths focusses at different distances. Other forms of aberration are due to off-axis light striking different areas of the lens at different angles (coma, of-axis astigmatism).
Ratio of focal length to lens diameter
||Indicates shutter speed required for exposure|
|Magnification at N (usually 25cm)||
||Magnification perceived by single-lens magnifying glass for relaxed human eye|
||Magnification achieved by Keplerian telescope.|
|Magnification achieved by compound microscope|
Read the following weblecture before chat: Microscope and Telescope Optics
Use the Zeiss interactive tutorial on Microsope characteristics to see how changing field lighting changes the microscope optics..
Chat Preparation Activities
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