Elementary Optical Concepts - The University of Chicagoastro.uchicago.edu/yerkes/docs/AstronomerTalks/AlHarper-Elementary... · Eyepiece lens Objective lens Image Elementary Optical

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

Inverted imageObject

Elementary Optical ConceptsA Simple Camera

f

ab

Thin lens formula: 1/f = (1/a) + (1/b)

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and PupilsThe exit pupil is an image of the entrance pupil formed by the eyepiece lens.

Basic layout of a Keplerian telescope.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

Inverted imageObject

Elementary Optical ConceptsA Simple Camera

f

ab

Thin lens formula: 1/f = (1/a) + (1/b)

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and PupilsThe exit pupil is an image of the entrance pupil formed by the eyepiece lens.

Basic layout of a Keplerian telescope.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and PupilsThe exit pupil is an image of the entrance pupil formed by the eyepiece lens.

Basic layout of the Keplerian telescope.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Telescope magni�cation

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and Pupils

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

Inverted imageObject

Elementary Optical ConceptsA Simple Camera

f

ab

Thin lens formula: 1/f = (1/a) + (1/b)

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

The eye is an integral part of the “telescope system”

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and PupilsThe exit pupil is an image of the entrance pupil formed by the eyepiece lens.

Basic layout of a Keplerian telescope.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

Inverted imageObject

Elementary Optical ConceptsA Simple Camera

f

ab

Thin lens formula: 1/f = (1/a) + (1/b)

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

The eye is an integral part of the “telescope system”

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and PupilsThe exit pupil is an image of the entrance pupil formed by the eyepiece lens.

Basic layout of a Keplerian telescope.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

Entrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

Collimated light: light rays from individual image points are parallel.

Objective lensEyepiece lens

Image

Elementary Optical ConceptsA Simple Keplerian Telescope

Inverted imageObject

Elementary Optical ConceptsA Simple Camera

f

ab

Thin lens formula: 1/f = (1/a) + (1/b)

O�-axis light raysEntrance pupil

Exit pupil

Field plane(or image plane)

Pupil diameter = D/Mag

(Diameter = D)

feyepiece fobjective

Telescopes magnify angles

Mag = fobj/feye

The eye is an integral part of the “telescope system”

Collimated light: light rays from individual image points are parallel.

Telescope magni�cationFields and PupilsThe exit pupil is an image of the entrance pupil formed by the eyepiece lens.

Basic layout of a Keplerian telescope.

“Night glasses” and “richest -!eld’ telescopes

• If the exit pupil of a telescope is bigger than about 7mm, all the lightwon’t enter our dark-adapted eye

• A “rich-field” telescope has just the right focal length eyepiece lens togive us all the light we can use and no more

• The objective lenses of 7x50 binoculars are just the right size to giveus all the light we can use from a seven-power telescope

• Questions– What is the magnification of the telescope in our example?– What’s the “richest-field” objective lens diameter for our telescope?– Why might we want to use a higher power eyepiece, even if it gives us an

exit pupil smaller than 7 mm?– What power eyepiece would give us “richest field” performance with an

8-inch diameter telescope with a focal length of 40 inches?– What would be the focal length of a “rich field” eyepiece for our 8-inch,

f/5 telescope?– Why wouldn’t we want binoculars with larger diameter objective lenses

than 50 mm?