Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Lecture Notes Animals Vision and Diffraction

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Goals Biology: To learn about the effect of pupil size on the ability to see clearly at large distances. Physics: To discuss the limits of visual resolvability imposed by diffraction of light through the pupil of the mammalian eye. Vision and Diffraction

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Big Ideas Biology: Eagles have a larger pupil size than we do for similar lighting conditions. Physics: Light entering the eye from a point source will fall on the retina with a central maximum whose center to edge subtends an angle θ 1 = 1.22 λ eye /D. Rayleigh’s criterion states that if the angle,θ, the two point sources make with your eyes is less than θ 1 then you will not be able to resolve that there are two distinct points. Vision and Diffraction

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Vision and Diffraction Vision Light enters your eyes passing through your pupils and is focused somewhere on the retina depending on what angle the source of the light enters your eyes. pupil

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Diffraction Vision and Diffraction At the retina the central maximum will make an angle θ 1 from center to edge with respect to your pupil. Point source D θ1θ1

Phy sics and Astronomy Outreach Program at the University of British Columbia Phy sics and Astronomy Outreach Program at the University of British Columbia Rayleigh’s Criterion Vision and Diffraction If θ  θ 1 the points are resolvable

Phy sics and Astronomy Outreach Program at the University of British Columbia Phy sics and Astronomy Outreach Program at the University of British Columbia Rayleigh’s Criterion Vision and Diffraction Rayleigh’s criterion: If the two central maxima are closer than their radius the two central maxima can not be resolved.

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Pupil size effects Vision and Diffraction θ θ = θ 1 θ θ > θ 1 For a pupil size where the point sources are barely resolvable, the point source would still be resolvable for a larger pupil size. The minium angle of resolution, θ 1, is inversely proportional to pupil size.

Phy sics and Astronomy Outreach Program at the University of British Columbia Phy sics and Astronomy Outreach Program at the University of British Columbia Birds of prey Vision and Diffraction CreaturePupil diameter (mm) [4] Human2.5 Bald eagle9 Great horned owl15 Red-shouldered hawk8

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Conclusions Vision and Diffraction Having a larger pupil size means that the minimum angle of resolution θ 1 is smaller. For a fixed separation between the point sources the points sources can be further away and still resolvable for a larger pupil size. Birds of prey such as eagles,owls and hawks have larger pupil size and can resolve distant objects more clearly

Physics and Astronomy Outreach Program at the University of British Columbia Physics and Astronomy Outreach Program at the University of British Columbia Bibliography [1] Image of eye from [2] Image of pupil from [3] Image of owl from [4] The Journal of Experimental Biology 211, Vision and Diffraction