Q: A camera uses a converging lens to project a real image onto an electronic detector. If the focal length of the lens is $$f$$ and the lens diameter is $$d$$, what is the correct expression for the f-number of the camera?

$$f\text{-number} = \dfrac{f}{d}$$

Question 1

A camera uses a converging lens to project a real image onto an electronic detector. If the focal length of the lens is $$f$$ and the lens diameter is $$d$$, what is the correct expression for the f-number of the camera?

Accepted Answer

$$f	ext{-number} = \dfrac{f}{d}$$

Question 2

Which part of the human eye is primarily responsible for most of the eye’s refraction due to its curvature and the large difference in the indices of refraction?

Accepted Answer

The cornea

Question 3

A person with myopia has a far point of 2 m. If a corrective lens is placed 1.5 cm from the eye, what is the required focal length of the lens to correct her vision? (Assume the image should be formed at the far point.)

Accepted Answer

$$f = -1.985\ \mathrm{m}$$

Question 4

Which of the following best describes the correction for hyperopia (farsightedness)?

Accepted Answer

A converging lens forms a virtual image at the near point.

Question 5

In a microscope, the objective lens has a focal length $$f_o$$ and the eyepiece has a focal length $$f_e. If $$the tube length is $$L$$, what is the magnification produced by the objective lens?

Accepted Answer

$$m_o = -\dfrac{L}{f_o}$$

Question 6

A simple magnifier is used to view an object placed just inside its focal point. If the focal length of the lens is $$f$$, what is the angular magnification $$m of $$the magnifier?

Accepted Answer

$$m = \dfrac{25\ \mathrm{cm}}{f}$$

Question 7

A microscope has an objective lens with $$f_o = 4.0\ \mathrm{cm}$$, an eyepiece with $$f_e = 8.0\ \mathrm{cm}$$, and the distance between the lenses is $$25.0\ \mathrm{cm}. $$What is the tube length $$L$$?

Accepted Answer

$$L = 17.0\ \mathrm{cm}$$

Question 8

If the image produced by the objective lens of a microscope is just inside the focal point of the eyepiece, what type of image does the eyepiece produce?

Accepted Answer

A virtual, upright image

Question 9

Which of the following statements about the iris in the human eye is correct?

Accepted Answer

It determines the amount of light entering the eye.

Question 10

A camera is focused by moving the lens rather than the detector. What is the main reason for this design choice?

Accepted Answer

Moving the lens allows for a fixed image plane and easier mechanical design.

Question 11

A person with myopia has a far point of 1.5 m. What is the optical power $$P (in $$diopters) of the corrective lens needed if the lens is placed very close to the eye?

Accepted Answer

$$P = -0.67\ \mathrm{D}$$

Question 12

Which of the following best describes the process of accommodation in the human eye?

Accepted Answer

Changing the shape of the lens to adjust the focal length.

Question 13

A microscope’s overall angular magnification is given by $$m = m_o m_e. If$$ $$m_o = -4$$ and $$m_e = 5$$, what is the overall magnification?

Accepted Answer

$$m = -20$$

Question 14

If the aperture of a camera is decreased (smaller $$d$$), what is the effect on the depth of field and the exposure?

Accepted Answer

Depth of field increases, exposure decreases

Question 15

A person with hyperopia has a near point of 50 cm. What type of lens is needed to correct their vision, and what is the sign of its focal length?

Accepted Answer

Converging lens, positive focal length

Question 16

In a two-lens system, after finding the image distance $$i_1$$ from the first lens, how do you determine the object distance $$p_2$$ for the second lens if the image is beyond the second lens?

Accepted Answer

$$p_2 is $$negative and equal to the distance from the second lens to the image

Optical Instruments: Cameras, Human Eye, Vision Correction, Magnifiers, and Microscopes

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