basic optical concepts 2.1 Flashcards
what does the geometrical optics approximation assume ?
light travels as rays in a homogeneous medium (same everywhere)
what are wavefronts ?
surfaces of constant phase or constant optical distance from the source
what is a phase ?
point in cycle of wave
e.g. peak of wave
what is optical distance ?
geometrical distance x refractive index
what is the link between wavefronts and rays?
wavefronts in geometrical approximation are always at right angle to rays
why are wavefronts at right angle to rays ?
they are surface of constant optical distance from the objects
what is the paraxial optics approximation ?
. all rays from an object intersect at an image point - this is also known as ideal image formation
what are the two classes of optical systems ?
. some optical systems collect light
e.g. solar panels
. majority of optical systems are image forming optical systems
e.g. eye- positive
what are spherical surfaces ?
. natural shape when two surfaces were together
e.g. ball and socket joint in hip
what do spherical surfaces do ?
. form images of objects
. they also have the ability to take light from objects but can bring light back together
what laws predict ideal image formation ?
.snell’s law and paraxial approximation
. if we know where object is we can know where image is
what do lenses form ?
images
how many surfaces do lenses usually have ?
usually have 2 spherical surfaces
sometimes we can have aspheric lens
what is property of a positive lens ( convex )?
. thicker at centre than edge
. light which passes through it to converge producing real image
. converging lens
. magnify
what is property of negative lens ( concave ) ?
. thinner at centre than edge
. diverging light leaving lens
. image is produced at same side as object
what is difference between converging and diverging lens ?
.converging has a positive focal length and produces real image
.diverging has a negative focal length and can form real or virtual image
what is the difference between real and virtual object?
real object - produces divergent light striking lens
virtual object - converging light striking lens
what is the difference between real and virtual image ?
real image - converging light leaving lens
virtual image - diverging light leaving lens
what happens when you look at an objects with a negative lens ?
. object is real
. image formed by negative lens is virtual
. image formed at the back of your eye is real
what happens when you view a test chart 6m away with a negative lens ?
. object is real and image formed by negative lens is virtual
what is vergence ?
angle formed by rays of light that are not perfectly parallel to one another
what is reduced vergence linked to ?
linked to the curvature of the wavefront and its measured in D
what happens to the value of reduced vergence as the light proceeds away from the object ?
the value increases
because value becomes less negative
what is the equation for reduced vergence ?
L = n/l
measured in D
in air n=1
. reduced vergence is not same as curvature unless refractive index is air
what is axial object/image ?
. lie on optical axis
. important when interested in location
what are off-axis objects / images ?
. lie above or below the optical axis
. shows magnification
. show heights of objects / images
-shows location of off axis object and image location
What does an axial image form?
produces an axial object
What is an optical axis?
- axial lies on here
- hypothetical line which passes through the centres of curvature on optical systems/surfaces
Light diverges from a point object. What happens to the values of the reduced vergence as the light proceeds away from the object?
they increase
