Geo Optics Flashcards
Vergence of light
-=diverging \+=converging L=object vergence L’=image vergence L’=F+L
L<0
Real object
L>0
Virtual object
L’<0
Virtual image
L’>0
Real image
Object location
l=n1/L
N1=RI of material in which light travels before hitting lens (left)
Image location
l’=n2/L’
N2=RI after passing through the lens (right)
Concave
Interface wraps around lower medium
Always diverging
Does not matter which way light travels
Convex
Interface wraps around higher medium
Always converging
Does not matter which way light travels
Power of SSRI
F=(n2-n1)/r
Radius of curvature
- if shape of lens surface is a C, it s a POSITIVE ROC
- if backwards C, negative ROC
Secondary focal points
- location of image point when plane-polarized light (light from infinity) incident on interface
- converging=to the right (real image)
- diverging=to the left (virtual)
- F’
Secondary focal length
- distance from interface to F-
- f’=n2/F
- f’
Primary focal point
- location of an object from which light can leave such that after interacting with interface, it exits as plane waves
- F
Primary focal length
- distance from interface to F
- f=(-)n1/F
- f
- focal points inverse of lens power
What is the inverse of the lens power
Focal points
Nodal point
Point on the axis through which light passes undeviated
Flat surface
- r=infinity, so F=0
- n1/l=n2/l’
- apparent depth questions are asking where the image is located relative to flat surface (objects apparent distance=image location)
Lateral magnification (linear mag)
- ratio of image size to object size
- AKA linear magnification
- m=hi/ho=L/L’=l’/l
- hi=height if image, ho=height of object
- L=incoming vergence, L’=outgoing vergence
- l’=image distance from lens, l=object distance
-l’/l ONLY if object and image in the same RI
Snells law
Relationship between angle refraction and angle of incidence
N1sin(theta)1=n2sin(theta)2
Total internal reflection
n20c will be totally internally reflected
- gloat incident at an angle greater than 0c will be refracted internally
- sin0c=n2/n1
- example is viewing AC angle unaided, must have gonio lens to view
Power of thin lens
- treated as 2 SSRIs
- calculate power of each and then add them to get total power
- F=F1+F2
Downstream vergence
- when you place a lens some distance (x) in front of a screen, the vergence of light striking the screen is different than the vergence of light leaving the lens
- Leff=L/(1-dL)
- light loses vergence as it travels further away from the object
Power and vertex distance
- effective power of lens changes depending on where the lens is located in front of the eye
- plus lenses=effectively weaker as they move closer to cornea. Hyperopes need more (+) in CL
- minus lenses=effective stronger as they move closer to cornea. Myopes need less (-) in CL
Fc=Fg/(1-dFg_
Any lens moving farther from the eye needs ____power
More +
Any lens moving closer to the eye needs more _____ power
Minus
Thick lenses
Can be thought of as 2 thin lenses representing the front and back lens surfaces, separated by some material
2 approaches to thick lenses
- Thick lenses can be though of as 2 thin lenses, representing the front and back lens surface, separated by some material of index n equal to index of lens. Successive imaging
- Use Gauss system (probably dont do this): power of a thin lens that would be equivalent (optically) to a particular thick lens
- Fv=F2 + F1/(1-(t/n2)F1)
Aperture stop
Light limiter
- physical entity that limits the amount of light passing into an optical system
- anatomical aperture stop of eye=pupil
Field stop
Limited the size of object that can be imaged by the system
Entrance pupil
Image of aperture stop bu lenses in front of it
- image of aperture stop formed by all of he lenses in front of it
- if no lenses in front of it, the entrance pupil itself i the ap stop
Exit pupil
Image of Ap stop formed by all lenses behind it
-if no lenses behind it, exit pupil itself is the ap stop
Entrance port
Image of field stop formed by lenses in front of it
Exit port
Image of field stop formed by lenses behind it
Depth of focus
Internal surrounding the RETINA in which an eye sees an object as in forces
-pinhole=increased depth of focus. Distinguishes refractive errors from other problems
Depth of field
Interval surrounding the fixation plane in which an object can reside and still be in focus
- short focal length=increased depth of field
- decreased ap size=increased depth of field and focus
Field of view
- extend of object plane that is imaged
- angle or liner
- angle of 1/2 illumination
- minus lens=increased field of view
- plus lenses=decreased field of view
Field of fixation
Angle made from the optical axis by the entrance port as measured as the center of the eye (14mm from cornea)
Stigmatic system
Point source produces point image
Astigmatic system
- pair of focal lines
- power is differnet in different meridians
- location of the vertical focal line is determined by the power in the horizontal median of the lens, and the location fo the horiztonal focal line is determined by the power in the vertical meridian of the lens.
- vertical power produces horizontal image
- horizontal power produces vertical image
Cylindrical lenses
- direction parallel to the axis of the cylinder is referred to as the axis meridian
- direction perpendicular to the axis meridian is the power meridian
- cylinder lenses always have zero power along one meridian
Spherical lens
Symmetric
Power in each meridian is the same
Contraocular view
- view dr would have when looking at the patient
- vertical meridian labels 90 degrees, horizontal labeled 180 degrees
Labeling cylindrical lens
- Specify location of axis using x
2. Specify power in a given meridian using the @ symbol
Circle of least confusion
- point of best focus for a lens
- dioptrically 1/2 way between the 2 line images that are formed in the principle meridians
- we are finding the point where the image is distorted equally in each meridian
- when using spherical equivalent, we assume COLC will fall on retina
DIOPTERS
Interval of sturm
- distance between the 2 foci of he principle meridians
- it is the linear distance between the locations of the horizontal and vertical line formations
LINEAR
Induced sphere and cyl with tilted lenses
- panto Tilt=rotating about the 180
- faceform=rotating about 90
Panto tile of minus lens will induce
Minus cyl at 180
Panto tile of plus lens will induce
Minus cyl x 090
Faceform of minus lens will induce
Minus cyl at 090
Faceform Ttilt of plus lens will induce
Minus cyl x 180
Mirrors ROC
Minus number
Power of mirrors
F=-2n/r
Convex mirror
Diverging
Concave mirror
Converging
Lens mirror combo equation
F=2F1+F2
