Week 2 Flashcards
Depth of focus
- the interval surrounding the retina where an eye sees and object in focus
- behind the eye
Depth of field
The interval surrounding the fixation plane where an object will still be in focus and there will be no perceivable blur on the retina
-out in space
Focal ratio
-f number/f-stop/ f/stop
Focal length/diameter of aperture
-diopters
Trends of focal ratio
- shorter focal length gives a larger depth of field
- increase in aperture size leads to decreased depth of field and decreased depth of focus
- larger f/stop: fewer aberrations, larger depth of focus
- smaller f/stop: gives brighter image, narrows focus
Hyperfocal distance
A distance at which a camera or system is focused so that the distal limit of the depth of field is at optical infinity
Depth of field trends
- increase in f-stop(decrease in aperture size) = larger depth of field
- decrease in f/stop(increase in aperture size)= smaller depth of field
Computation of geometrical blur size
Blur(mad)=defocus X pupil size in mm
Blur(minutes)= 3.44 X D X pupil size in mm
Small pupil advantage
Increase the depth of focus and decrease the blur, compensate for loss of accommodation in old age
-better night vision
Methods for reducing pupil size
Artificial pupil, artificial iris, moo tic agent
Disadvantage of adding just adding an artificial pupil
Decreased field of view!
-creates an additional field stop or aperture stop
parallel wavefront
-collimated light
spherical wavefront
- converging light beam
- diverging light beam
Wave aberration
- the deviation of a wavefront in an optical system from a desired prefect planar wavefront
- away from the predictions of the paraxial optics
aberrations
- failure for the light rays passing through an optical system to converge at one point
- possibly due to defects or limitations of the system
first order aberrations
- piston (move the whole thing up or down)
- tilit(the plane is tipped in one direction)
Second order aberrations
- defocus (spherical correction)
- astigmatism(cyl correction)
higher order aberrations
Most common: spherical then coma
Zernike polynomials
-set of basic shapes that are used to fit the wavefront
Properties of zernike polynomials
- orthogonal(terms are not similar so they can be separated and looked at individually)
- normalized( sum of vectors)
- efficient(shapes are similar to typical aberrations found in the eye)
strum’s interval
-the difference between the focal points(points of focus) of each meridian
Circle of least confusion
-point between the points of focus of the two meridians where each meridian is equally burred
spherical aberration
-only aberration that occurs for both on-axis and off-axis object points
Positive spherical aberration
-peripheral rays intersect closer to the lens that central
Negative spherical aberration
-peripheral rays intersect after the central rays
prolate ellipse
-more curved in the center
oblate ellipse
-more curved at the top
coma aberration
- comet shaped pattern caused by off-axis point source passing through a spherical system
- associated with kertaconus
pilots have more what?
-vertical coma
oblique/marginal/radial astigmatism
- off axis light coming through cylindrical system
- glasses that bend around your face and not flat can induce this
recognize barrel and pincushion distortino
-barrel is rounded and pincushion is flatter
rayleigh resolution limit
- limit distance so that you still have two dots
- between resolved and unresolved point sources
minimum angle of resolution and pupil size relation
-smaller pupil means larger min angle means worse resolution
what is the idea pupil size?
2mm
diffraction
-causes light to bend perpendicular to the direction of the diffracting edge
interferene
causes the diffracted light to have peaks and valleys
airy disk
- light through circular aperture results in this
- description of the best focused spot of light that a perfect lens can make, limited by diffraction of light
what is the one limitation of the image quality of an optical system?
-diffraction limit
