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Outline - PowerPoint PPT Presentation

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  1. Outline • Focus • Photo-transduction • Sensitivity / resolution trade-off • Measuring the optical quality of the eye • Linear systems analysis

  2. Focus - the lens equation

  3. Accommodation - bringing objects into focus Focused on Focused on

  4. Some numbers • Refractive power of cornea • 43 diopters • Refractive power of lens • 17 - 25 diopters • Other eyes • Diving ducks - 80 diopter accommodation range • Anableps - two pairs of eyes with different focusing power

  5. Accommodation errors(focus problems) • Myopia • Near-sightedness • Emmetropia • Far-sightedness

  6. Accomodation errors(focus problems) • Myopia • Near-sightedness • Emmetropia • Far-sightedness • Presbyopia • Hardening of lense with age (cannot accommodate to near objects)

  7. Depth of Field (DOF) • DOF = range of depths at which objects are “reasonably” in focus • E.g., at which blur is less than some threshold limit. • How can one increase one’s depth of field?

  8. Transduction in the retina

  9. Isomerized (bleached) photopigment retinal opsin

  10. Sensitivity / resolution trade-off • Increase sensitivity => decrease resolution • Increase resolution => decrease sensitivity

  11. Sensitivity / resolution trade-off • Increase sensitivity => decrease resolution • Increase resolution => decrease sensitivity • One example - changing pupil size Increased spatial resolution Shrink pupil Decreased sensitivity

  12. Other examples

  13. Other examples • Wavelength • Time • Wavelength

  14. Duplicity Theory: Two receptor systems • Cones • Encode wavelength information • High resolution image coding in fovea • Low sensitivity • Rods • High sensitivity • Concentrated in periphery • Lower resolution coding in periphery

  15. Part 2 of solution to sensitivity / resolution trade-off • Foveal coding • One-to-one connections from cone receptors to bipolar cells and from bipolar cells to ganglion cells • Peripheral coding (neural pooling) • Many-to-one connections from receptors to bipolar cells Periphery Fovea Receptors Bipolar cells

  16. General solution to sensitivity / resolution trade-off • Place high resolution / low sensitivity system in fovea • Place high sensitivity / low resolution system in periphery • Use eye movements to obtain high resolution images of peripheral objects

  17. Measuring the resolution of the eye • The point spread function • Spatial frequency analysis - the modulation transfer function

  18. Measuring the resolution of the eye • The point spread function • Spatial frequency analysis - the modulation transfer function

  19. Visual angle

  20. Point spread

  21. Point spread function