Flashcards Chapter 26

What is the main function of the eye in terms of optics?

To focus light onto the retina for image formation

What part of the eye provides most of the eye's focusing power?

The cornea

Which part of the eye adjusts its shape to focus on near or far objects?

The lens

What is the typical power of the eye in diopters (D)?

50 D to 54 D

How is the power of a lens calculated?

P=\frac{1}{f} where f is in meters

What is the typical focal length of the relaxed human eye?

About 2 cm (corresponding to a power of 50 D)

What is the near point?

The closest point at which the eye can focus comfortably

What is accommodation?

The eye’s ability to change lens shape to focus on near objects

What causes farsightedness (hyperopia)?

The eyeball is too short, light focuses behind the retina

What type of lens corrects farsightedness?

A converging (positive power) lens

What causes nearsightedness (myopia)?

The eyeball is too long, light focuses in front of the retina

What type of lens corrects nearsightedness?

A diverging (negative power) lens

What is the far point for a myopic eye?

The farthest distance the eye can focus clearly

What lens power is needed to move the far point to infinity?

P = -1/(far point in meters)

What does 20/20 vision mean?

Normal visual acuity, you can see at 20 feet what a normal eye sees at 20 feet

What kind of lenses do reading glasses use?

Converging lenses (positive power)

Why does lens accommodation decrease with age?

The lens becomes less flexible, leading to presbyopia

What defines a color?

The wavelength of light entering the eye

What are the six basic colors perceived by humans?

Red, orange, yellow, green, blue, violet

What is the simple theory of color?

Color is perceived based on which wavelengths of visible light an object reflects or emits

Which photoreceptors detect light intensity, not color?

Rods

What colors do cones in the human eye respond to?

Red, green, and blue

What is hue?

The color family

What does the color of an object depend on?

The light it reflects and the illumination

What is color constancy?

The tendency of perceived color to remain constant under varying lighting

What is the Retinex theory?

The brain adjusts perceived color based on comparison across the visual field

What are the two lenses in a compound microscope?

Objective lens and eyepiece (ocular lens)

What type of image does the objective form in a compound microscope?

A real, inverted, magnified image

What type of image does the eyepiece form in a compound microscope?

A virtual, magnified image

What is the total magnification of a microscope?

m = m_o\cdot m_e

What is the typical arrangement of a compound microscope?

The objective lens forms a real, inverted image near the focal point of the eyepiece lens, which then magnifies this image to produce a virtual, enlarged view

What is the approximate lens separation L?

Roughly equal to the image distance of the objective

What is numerical aperture (NA)?

NA = n \sin \alpha, a measure of light gathering ability

How does NA affect resolution?

Higher NA improves resolution

What is the f-number?

The ratio f/D, where f is focal length and D is aperture diameter

What is the main purpose of a telescope?

To collect light and magnify distant objects

What kind of image does a simple two-lens telescope form?

A virtual, inverted image

How is angular magnification calculated?

m = f_0/f_e , where f_o is the focal length of the objective

Why is the final image from a telescope inverted?

Due to the two converging lenses forming an inverted real image, then re-magnified

What are aberrations?

Image distortions due to lens shape, material, or imperfections