Fifteen Questions - Workshop 1 Location Week 7

Light and Lenses


1. The speed of light is medium dependant.  Which means it changes speed depending on what it is travelling through.  Does it get slower or faster travelling through denser mediums. Yes or no? 
   Yes, light moves slower through denser mediums.  This is a result of there being more particles to move through. 


2. If light enters glass at an angle other then 90 degrees what happens to it? 
   The light will refract.


3. Light travels in waves.  What is the measurement for this?
   


4. What is the degree of the refraction of light dependant on? And which colour is refracted the most?
   Cannot be greater then 90 degrees. Red light is refracted the most. 


5. What is the angle of incidence? 
   The angle at which light strikes a surface.


6. What is the refractive index of material?
   n = c/v
n = reflective index
c = speed in vacuum
v = speed in other medium


7. What is the difference between a convergent and divergent lens?
   Convergent is a positive, double convex lens and Divergent is a negative, double convex lens. 


8. What is the focal length of an optical system?


9. What are circles of confusion? 
   In optics a circle of confusion is an optical spot caused by a cone of light rays from a lens not coming to a perfect focus when imaging a point source.


10. What is the angle of view on a lens? 
   Angle of view is the subject coverage as measured across the format diagonal (x) in degrees but is usually more practical to measure across the longest dimension (y)


11. What is the covering power of a lens?
   The maximum area of a scene that can be recorded with good definition by a particular lens.


12. What lenses alter perspective?
   Wide angle lenses as well as fish eye.


13. What is geometric distortion? 
   


14. What is the equation to calculate correct viewing distance? 
And, PROBLEM to solve: 
You need to make a vertical portrait using 24x36mm format which will be used on a roadside billboard where the photo will be 5m high and it will be ideally seen from 50m. What lens focal length should you use to maintain 'correct' seen perspective?
Given: image height = 36mm
print height = 5000mm (5m) 
viewing distance (VD) = 50,000mm (50m)
Unknown:magnification (M) = print / image 
= 5000 / 36 = 139x
focal length (f) = ?


15. For the following lens types, write a description of each using no more than 10 words for each lens.
- Wide angle
   Wider angle of view than normal
- Zoom
   Variable focal length 
- Long focus
   Narrow angle of view, simple but large and heavy in confusion
- Telephoto
   Long but shorter than focal length would suggest
- Retro focus
   Shorter than back focal distance would suggest
- Quasi fish eye
   Circle of illumination circumscribes format
- True fish eye
   Circle of illumination sits within format
- Catadioptric
   Use of two concave mirrors = 'compact' long lens very long lens 
- Macro
   Allows closer than 'normal' focusing
- Teleconverter
   Sits behind lens. eg. 2X converter doubles existing lens focal length
- Supplementary or close up lens
   Screws to lens front allowing closer focusing and greater magnification
- PC or tilt shift lens
   Group of elements can shift laterally and tilt/swing.