### device | lense:

Photographic lense
* are a great resource for vision systems.
* vary in quality and size.

Plastic lense
* are light weight and can be molded into comfortable shapes.
* bend when held tightly by frames.

Polycarbonate lense
* are also much thinner and lighter than glass or plastic lenses.
* are high index and are usually the lightest, most comfortable lenses
  - usually provide the lightest, most comfortable lenses
  - more shatter resistant and therefore much safer glasses
  - superior to glass and plastics in strength and impact resistance
* provide high impact strength
  - protection from standard UV radiation

Progressive lense
* offer wearers one continuous field of vision to see clearly at all distances.
* provide clear vision at all distances in one lens.
* work by basically buffing the bifocal line into the lens so it blends.

Soft lense
* Some soft lenses do absorb organic vapors and corrosive vapors like hydrogen chloride or ammonia.
* absorb chemicals from the water.
* are brittle when dry and break easily
  - more expensive than gas permeable lenses
  - suitable for correcting most refractive errors
  - very delicate and tear easily
* can correct many vision problems
  - dry out in winds and dry areas
* retain organic vapors long after exposure.
* tend to trap vapors which can irritate the eye.

Zoom lense
* Most zoom lenses have macro focusing, which means the lens can focus close up
  - one-touch zoom control
* have a variable focal length.

### device:

Light source
* All light sources used for lighting lose their ability to produce light as they age.
* Any light source emits a very large number of photons of light oriented at random
  - has a specific spectral quality
* Every light source is different, but the intensity changes in the same way.
* Most light sources are incandescent lamps
  - mixtures of various wavelengths of light
  - contain UV, including sunlight, flourescent, and incandescent bulbs
* Most light sources emit a broad range of wavelengths that cover the entire visible light spectrum
  - mixture of wavelengths
  - light at many different wavelengths
  - unpolarized light, but there are several ways light can be polarized
  - provide a fairly complete spectrum with virtually all of the wavelengths present
* Some light sources emit radiation
  - flash on and off many times a second
  - provide light
* are different, so color balance becomes important with photomicrography
  - halogen and incandescent, providing upward, downward and diffused illumination
* are located in books
  - candles
  - flashlights
  - hallways
  - houses
  - light bulbs
  - skies
  - used for reads
* can be incandescent or LEDs.
* cause peaks in the incident radiance distribution.
* come in three basic types incandescent, arc and fluorescent.
* general term applied to any source of light used in photography.
* have no visible shape of their own.
* is very important in creating depth.
* produce a mixture of hues.
* vary greatly in their efficiency
  - in their ability to accurately reflect the true colors of people and objects

### device:

Loudspeaker
* Most loudspeakers are rectangles, which are only slightly better than squares
  - have dynamic ranges
* Most loudspeakers produce sound with traditional drivers
* Some loudspeakers have axis frequency responses.
* also vary widely in directivity with frequency.
* are actual emitters
  - an integral link in an audio system
  - located in sporting events
  - much larger than microphones because they have to handle much stronger signals
* cause sound waves when an electromagnet makes the speaker vibrate.
* do the opposite , converting incoming electrical energy into outgoing sound.
* includes sections.
* transmit the rise and fall of Arabic chanting.
* use vibration to generate sound.