L9 - reflective optical systems Flashcards
what is the law of reflection ?
angle of incidence = angle of reflection
i=i’
what kind of surfaces does reflection occur in ?
There are a number of conditions under which reflection can happen. These include mirror surfaces, typically silver, gold or aluminium surfaces for reflecting visible light1
what is property of mirror surfaces ?
Mirror surfaces do not transmit any of the light incident on them and they reflect most of the light.
how do smooth surfaces give us specular reflection ?
A smooth surface will reflect neighbouring rays travelling parallel to each other in the same way. The normals to each of these rays are parallel to each other and hence the amount of reflection depends only on the angle the rays are approaching the surface.
how do rough surfaces give us diffuse reflection ?
they are incident on parts of the surface that have different slopes due to the roughness of the surface. Although each ray is still reflected , the normals to these rays are no longer parallel to each other and there is a randomness which is introduced to the reflected angles.
why do diffuse reflections not able to produce image ?
not good at channeling information about objects , randomness is introduced in reflected angle therefore you can’t see your self
what happens in transparent optical surface ?
e.g. air- glass interface
the amount of light (100%) - reflected is 4% ,The remaining 96% is transmitted through the interface in the form of refracted light.
what does the amount of light reflected depend on ?
The amount of light reflected also depends on the angle of incidence – a larger percentage of light is reflected when the angle of incidence is large.
where do we observe reflections ?
We observe reflections from windows, water surfaces, spectacle lenses and indeed eyes even though all these materials are transparent and transmit light through them.
what happens when total internal reflection ?
no light is transmitted and it is behaving like a mirror with 100% of light reflecting with in glass
how much of light is reflected in longer wave length ?
100% of light will be reflected for long wavelength
what is object space ?
object rays travel towards optical system is the region to left of the mirror
what image space ?
image rays travel away from optical system and is also to left of mirror
where do both object and image space lie ?
both Object Space and Image Space lie on the left of the mirror
it is still convenient to treat them as two separate spaces, one containing object rays and one containing image rays.
what is the refractive index of image space for mirror ?
ni = −no
tool box - mirrors
L′ = L + F L = n/l and L′ = −n/l' F=-n/f =-n/f' M=h'/h =L/L' h'=-ntani/F F=n'-n/r f=r/2 -
what is the power of a spherical mirror and what can we conclude of it ?
F=-2n/r
An important conclusion of this Equation is that spherical mirrors with a negative radius of curvature have a positive power, that is they increase vergence
what are concave mirrors ?
Mirrors with a negative radius of cur- vature, and hence positive power, are concave mirrors and they are the mirror equivalent of a positive thin lens.
what are convex mirrors ?
Mirrors with a positive radius of curvature, and negative power, are convex mirrors and are the mirror equivalent of negative thin lenses
what does the equation f=r/2 mean ?
This means that the focal points of a spherical mirror are always located half way between the mirror and the centre of curvature of the mirror
what are the reflections in the eye ?
As light enters the eye it needs to cross a number of optical interfaces, namely the front and back corneal surfaces and the front and back lens surfaces
what are the four reflections in the eye due to ?
The four reflections due to the four optical surfaces in the eye are called the Purkinje images and are due to specular reflections.
what is the first purkinjie image due to ?
is due to the reflection from the anterior corneal surface and is the strongest of these reflections
how do you get the most reflection ?
the larger the difference in refractive indices, the larger the reflection and the interface between air and the cornea offers the biggest refractive index step in the eye.
what is the second and third and fourth purkinjie image due to ?
2- is due to the posterior corneal surface and is the weakest reflection (0.02%)
3 and 4 -are due to the anterior and posterior lens surfaces respectively and are of equal brightness (0.1%).
what is purkinjie image useful for ?
for corneal topography
shapes of ring used to determine shape of cornea and is useful for fitting cl
do diffuse reflections occur in the eye ?
The eye also reflects light in a diffuse manner.
only way to visualise internal structure
What does a mirror consist if?
anything that can reflect light, metallic surfaces or transparent optical surfaces b y total internal reflection or any other interface where there is a reflection, mirrors of specular surfaces
What is a spherical mirror?
an imaging system
