Week 3 Flashcards
What lenses can give you inverted images?
-only plus lenses!!!!(convex)
What lenses can give you magnified images?
-only plus lenses!!!!(convex)
What lenses can give you an image that is 1/2 the size of the object?
-both convex and concave lenses
What lenses can give you an image that is 2 times the size of the object?
-only plus lenses!!!(convex)
Where are the front and back focal lengths measured from?
-measured from vertex of the lens
Where are the effective focal lengths measured from?
-measured from principal planes
What is the power of the human eye?
- cornea=+40D
- Crystalline lens=+20D
What kind of image is projected on the retina?
- small
- inverted
- real
Why is the human eye a plus lens?
-the index of refraction of the aqueous solution it sits in gives it a plus power
Microscope lens set up
- two lens structure
- both plus lenses
- image from the first lens is the object of the second lens
Microscope imaging
- object for second lens is image from the first
- object for second lens is on focal point, so image is projected at optical infinity
- magnified, virtual image
Magnification of a microscope and telescope
M=Mobjective*Meyepiece
Resolution Limit
- the SEPARATION between closest distinguishable points imaged through an optical instrument
- smaller the better(smaller separation=higher resolution)
- expressed in angle or length
Resolving Power
- the RECIPROCAL OF THE SEPARATION between the closest distinguishable points imaged through an optical instrument
- the larger the better
- expressed in inverse angle or inverse length
Resolution and resolving power
-dependent on wavelength
Resolution of the human eye
- 2mm for day light
- with wavelength, about 0.86 arcmin
Telescope structure
- two lens system
- light from distant object(optical infinity, collimated light)
- collimated beams exit second lens, with a smaller diameter than the ones that entered
Power of a telescope
- vergence is zero before AND after, so power is ZERO
- principal planes are at optical infinity
Compare microscope and telescope
Microscope: observe near object
- distance between lenses is larger than sum of focal lengths
- image is magnified, inverted, dim
- strong vergence for entering beam
Telescrope: observe distant object
- distance between lenses is equal to the sum on the focal lengths
- Image is minified, inverted, bright
Telescope magnification
- minifies object
- -changes the angle in which we see the object, not the size of the object!!
- looks 20-50 times larger than it would with the naked eye
Telescope resolution
- minimum angle of resolution=( 1.22* wavelength)/objective lens diameter
- a telescope with D=2, separation is 0.06 arcsec
Eye resolving power
Museful*angle of resolution
-0.3mrad
Field of view
-can have same magnification and different field of view
telescope resolution dependent factors
- higher resolution for smaller wavelength
- use blue filter for better resolution
- increase Diameter of lens for smaller/finer resolution
Kepler-type telescrope
- 2 plus lenses
- used in astronomy
- lenses separated by sum of focal lengths
- objective lens has larger diameter
- eye piece has higher power
Kepler-type telescope imaging
- image is virtual and at optical infinity
- image is inverted
Galilei-type telescope
- one plus(objective lens) and one minus(eye piece)
- used for terrestrial things
- lenses are separated by focal objective-focal eyepiece
- low vision aids
Galilei-type telescope imaging
-image is virtual and ERECT
Newtonian refractor
-adds a deviation mirroe
Catadioptric telescopes
-combination of refraction and diffraction
Radiotelescope
- uses radio waves instead of light
- hydrogen atom emission
Why do stars twinkle?
- atmosphere is non uniform lens
- pollution, scattering, hot/ cold, can alter images
Benefits to reflection
- no chromatic aberration
- only one surface precision
- no need for large volume of glass
- better support(less weight)
What is the primary shape large mirrors use for their little pieces?
Hexagonal
What electromagnetic waves are used for space observation?
IR
