Optics 2A: PUPILS, STOPS, AND RAYS

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22 Terms

1
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Aperture stop in camera

Adjustable diaphragm placed after first lens element

<p>Adjustable diaphragm placed after first lens element</p>
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Aperture stop in the eye

Clear opening formed by the iris

<p>Clear opening formed by the iris</p>
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<p>Properties affected/not affected by lens diameter</p>

Properties affected/not affected by lens diameter

Affected

  • Sharper image

  • Brighter image

  • Depth of field

Not affected

  • Size

  • Type

  • Location

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<p>In <u>collimated </u>illumination, the aperature stop is…</p>

In collimated illumination, the aperature stop is…

  • The smallest diameter opening

#3

<ul><li><p>The smallest diameter opening</p></li></ul><p><em>#3</em></p>
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Properties of aperature stop

  • Determines light gathering capacity of a system

  • Its edges form the smallest possible angle

    • Of an on-axis object point

  • Dependent on object locatoin

<ul><li><p>Determines light gathering capacity <u>of a system</u></p></li><li><p>Its edges form the smallest possible angle</p><ul><li><p>Of an on-axis object point</p></li></ul></li><li><p>Dependent on object locatoin</p></li></ul><p></p>
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Definition of ray height

Seperation of rays from optical axis

  • Ray height of 8mm

    • Maximum ray height is 4mm

    • 4mm above optical axis

    • 4mm below optical axis

  • Equal to the semi-diameter of the aperature

<p><strong>Seperation of rays from optical axis</strong></p><ul><li><p>Ray height of 8mm</p><ul><li><p><u>Maximum ray height</u> is 4mm</p></li><li><p>4mm above optical axis</p></li><li><p>4mm below optical axis</p></li></ul></li><li><p>Equal to the <u>semi-diameter</u> of the aperature</p></li></ul><p></p>
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Semi-diamter of an aperture

Half of the diameter of the aperature opening

<p>Half of the diameter of the aperature opening</p>
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Calculating angular subtense w/ optical axis

Tan^{-1}\left(\frac{Semi-diamter_{.}of.stop}{Distance.from.object}\right)

  • AKA aspect ratio

  • Element forming smallest angular subtense→ aperature stop

<p></p><p>$$Tan^{-1}\left(\frac{Semi-diamter_{.}of.stop}{Distance.from.object}\right)$$ </p><ul><li><p>AKA aspect ratio</p></li><li><p>Element forming smallest angular subtense→ aperature stop</p></li></ul><p></p>
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The aperature stop depends on…

  • Location of object

  • Semi-diamter of the stop or lens

<ul><li><p>Location of object</p></li><li><p>Semi-diamter of the stop or lens</p></li></ul><p></p>
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Determining apterature stop using marginal ray

  1. Draw ray from on-axis object that passes through all elements

  2. Mark height at which it intersects the elements

  3. Largest height / semi-diamter ratio

<ol><li><p>Draw ray from on-axis object that passes through all elements</p></li><li><p>Mark height at which it intersects the elements</p></li><li><p>Largest height / semi-diamter ratio</p></li></ol><p></p>
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Entrance pupil

  • Object-space image of the aperture stop

  • Formed by optical elements preceeding aperture

  • Aperature stop as seen from an axial point on the object

<ul><li><p>Object-space image of the aperture stop</p></li><li><p>Formed by optical elements preceeding aperture</p></li><li><p>Aperature stop <u>as seen from an axial point on the </u><strong><u>object</u></strong></p></li></ul><p></p>
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Exit pupil

  • Image-space image of the aperature stop

  • Formed by optical elements suceeding it

  • Aperature stop as seen from an axial point on the image

<ul><li><p>Image-space image of the aperature stop</p></li><li><p>Formed by optical elements suceeding it</p></li><li><p>Aperature stop <u>as seen from an axial point on the image</u></p></li></ul><p></p>
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The aperature stop is the entrance pupil when…

There is no lenses preceding the the AS

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The aperature stop is the exit pupil when…

There is lenses preceeding the aperture stop

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<p>Element one is…</p>

Element one is…

Aperature stop

Entrance pupil

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<p>The exit pupil is…</p>

The exit pupil is…

The image of element 1 via element 2

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Entrance pupil of the human eye

  • What we call the pupil (Apparent pupil)

  • Image of the iris via the cornea

  • Slightly closer to cornea and aobut 12.7% larger than the iris

<ul><li><p>What we call the pupil (Apparent pupil)</p></li><li><p>Image of the iris via the cornea</p></li><li><p>Slightly closer to cornea and aobut 12.7% larger than the iris</p></li></ul><p></p>
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Principal ray

  • Ray from off-axis object point → Center of entrance pupi → Lens

  • Ray = Refracted at lens

    • Refracted towards center of the exit pupil

<ul><li><p>Ray from <u>off-axis</u> object point → Center of entrance pupi → Lens</p></li><li><p>Ray = Refracted at lens</p><ul><li><p>Refracted towards center of the exit pupil</p></li></ul></li></ul><p></p>
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A ray from an off-axis object point crosses the center of the AS… It also crosses the…

Center of exit pupil

Center of entrance pupil

<p>Center of exit pupil</p><p>Center of entrance pupil</p>
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Marginal ray definition

  • Most extreme ray that propagates through the system unobstructed

  • Confines the cone from an on-axis object point

<ul><li><p>Most extreme ray that propagates through the system unobstructed</p></li><li><p>Confines the cone from an <u>on-axis</u> object point</p></li></ul><p></p>
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Finding marginal ray

  • Ray from on-axis object point → Edge of entrance pupil

  • Lens infront of AS→ Ray bends and passes edge of aperture stop

  • Lens after AS→ Ray bends and passes through exit pupil

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A ray from an on-axis object point crosses the edge of the AS… It also crosses the…

Edge of the entrance pupil

Edge of the exit pupil