The Principal of Optical Instruments.ppt

8/20/2019 The Principal of Optical Instruments.ppt

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Optical Instruments


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Cameras, Film, and Digital


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Cameras, Film, and Digital

A digital camera uses CCD sensors instead offilm. The digitized image is sent to a processor for

storage and later retrieval.


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Camera adjustments:

• hutter speed: A faster shutter speed ma!es a

sharper picture.

• f"stop: controls the ma#imum opening of the

shutter. This allo$s the right amount of light to

enter to properl% e#pose the film, and must &e

adjusted for e#ternal light conditions.

• Focusing: this adjusts the position of the lensso that the image is positioned on the film.


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Depth of field is the

amount of distance

&et$een the nearest and

farthest o&jects thatappear in accepta&l%

sharp focus in a

photograph.


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The 'uman (%e

The human e%e resem&les a camera in its

&asic functioning, $ith an adjusta&le lens, theiris, and the retina.


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Terms Description

Near point closest distance at which eyecan focus clearly. Normal isabout 25 cm

Far point farthest distance at which

object can be seen clearly.Normal is at infinity.

Nearsightedness far point is too close

Farsightedness near point is too far away.


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)earsightedness can &e corrected $ith a

diverging lens.


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Farsightedness can &e corrected $ith a

converging lens.


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*agnif%ing +lass

A magnif%ing glass simple magnifier- is a

converging lens. It allo$s us to focus on o&jects

closer than the near point, so that the% ma!e a

larger, and therefore clearer, image on the retina.


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*agnif%ing +lass

The po$er of a magnif%ing glass is descri&ed

&% its angular magnification:

If the e%e is rela#ed N is the near point distance

and f the focal length-:

If the e%e is focused at the near point:


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Telescopes

"t$o lenses at opposite ends of a long tu&e.

"The o&jective lens is closest to the o&ject

"the e%epiece is closest to the e%e.

"The magnification is given &%:

f / focal point of the o&jective

f e / focal point of the e%epiece


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"Compound lens s%stem is needed. 0ut it is too

heav%.

" To reduce spherical and chromatic a&erration,

para&olic mirror is used


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Terrestial Telescope

"!no$n as +alilean telescope

-1eal and inverted image is formed &% the

o&jective

-The image is then acts as an o&ject for the

e%epiece

-The e%epiece $ill form virtual inverted magnified

-Therefore final image is virtual upright andmagnified


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- Another t%pe, uses a third lens 2 inverting lens

- This $ill also produce upright images


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Compound *icroscopeA compound microscope has an o&jective converging lens-

and an e%epiece converging lens- a distance l apart. The o&ject

is placed close to the o&jective, to form an enlarged real imageI3, $hich is magnified &% the e%epiece acting as a magnif%ing

glass.


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The magnification is given &%:


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1esolution

- The distance at $hich a lens can &arel%

distinguish t$o separate o&jects.

- limited &% a&errations and &% diffraction.


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4imits of 1esolution5 Circular Apertures

For a circular aperture of diameter D, the centralma#imum has an angular $idth:


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4imits of 1esolution5 Circular Apertures

The 1a%leigh criterion states that t$o images are just resolva&le $hen the center of one pea! is

over the first minimum of the other.


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1esolution of Telescopes and

*icroscopes5 the λ 4imit

- resolution is directl% proportional to the$avelength

- inversel% proportional to the diameter,

- radio telescopes are &uilt to &e ver% large.

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The Principal of Optical Instruments.ppt