VLE 2 Optical Instruments I
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Myopia
Myopia:
Focal length of the eye lens too small, eye muscle cannot expand lens enough
image of for distance objects is in
front of the retina |
source: http://de.wikipedia.org/wiki/Kurzsichtigkeit (11.01.09) |
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Myopia and its correction with a defocussing |
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Correction by a defocussing lens |
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lens. |
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Hyperopia
Hyperopia :
Eye lens cannot get the necessary curve-radius image of close object behind the retina
Correction by focussing lens
source: http://de.wikipedia.org/wiki/Kurzsichtigkeit (11.01.09)
Hyperopia and its correction with a focussing lens.
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Optical spare representation
Spare lens
Focal length of the eye caused by:
Eye lens
Cornea
Aqueous fluid
Vitreous
source: Demtröder, Experimentalphysik 2
Spare representation of the eye with a lens with a focal length on the object side of f1 and on the image side f2 (outer boundary air, inner boundary vitreous).
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Spatial resolution and sensitivity of the eye
Eye lens
retina
source: Demtröder, Experimentalphysik 2
The closer an object is to the eye, the bigger it appears. This means the visual angle ε is bigger:
tan 2 12 Gs Gs
That the object with the distance g is imaged sharp onto the retina, |
f1 |
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f2 |
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the lens equation has to be fulfilled. |
g |
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b |
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The distance b of the retina is constant Adaption be changing of the focal length of the eye lens
Minimal distance smin = 10 cm
Clear distance s0 = 25 cm
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
2. Magnifying glass
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Magnifying glass
source: http://de.wikipedia.org/wiki/Lupe
Image
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Retina |
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Eye lens |
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Magnifying glass |
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source: Demtröder, Experimentalphysik 2
Aim of magnifying optical instruments is to increase the visual angle ε without going below the clear vision distance
anugular magnification V |
visual angle with instrument |
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visual angle 0 without instrument |
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The simplest magnifying optical instrument is the magnifying glass.
A magnifying glass is a focussing lens with a small focal length which is placed between eye and object in a way that the object is in the focal plane of the magnifying glass.
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Basic principle
Virtual image
Magnifying glass Eye
source: Demtröder, Experimentalphysik 2
The magnification of a magnifying glass is the ratio of the clear visual distance s0 (= 25 cm) and the focal lens f of the magnifying glass.
Magnification of a
Vergrößerung Lupe :
magnifying glass:
B
VL b
0 G s0
with GB bg VL sg0
for g f VL sf0
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
3. Telescope
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Basic principle
From far distance objects
Eye
Source: Demtröder, Experimentalphysik 2
V |
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B |
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f1 0 |
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f1 |
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f2 |
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F |
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f2 0 |
f2 0 |
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A telescope is built for magnifying objects in a far distance. A lens L1 (objective) with high focal length generates an intermediate image, which is imaged with a second lens (eye-piece). The eye-piece acts as magnifying glass. The magnification of the telescope is equal to the ratio of the focal length of objective and eye-piece.
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany
Keplerian telescope and Galileo's telescope
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Keplerian Telescope |
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L2 convex (f2>0) |
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Eye |
source: Wikipedia |
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Johannes Kepler (1571-1630) |
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Galileo's telescope
L2 concave (f2<0)
Eye
source: Wikipedia
Galileo Galilei (1564-1642)
source: Demtröder, Experimentalphysik 2
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Prof. M. Schmidt
Institute of Photonic Technologies, Univ. Erlangen, Germany