Q: What is the formula for the f-stop of a camera lens?

$$f\text{-}stop = \frac{f}{D}$$

Question 1

A camera uses a converging lens with a focal length of $$60.0\ \mathrm{mm}. If a$$ $$0.500\ \mathrm{m}$$ high flower vase is placed $$2.00\ \mathrm{m} in $$front of the lens, how far from the lens should the CCD be placed to obtain a sharp image?

Accepted Answer

$$61.9\ \mathrm{mm}$$

Question 2

Given a camera lens with a focal length $$f = 4\ \mathrm{cm}$$ and an aperture diameter $$D = 2\ \mathrm{cm}$$, what is the f-stop of the lens?

Accepted Answer

$$f/2$$

Question 3

A nearsighted person has a far point at $$10.0\ \mathrm{cm}$$ from the eye. If glasses are worn $$2.0\ \mathrm{cm} in $$front of the eye, what focal length should the glasses have to allow the person to see distant objects clearly?

Accepted Answer

$$-8.0\ \mathrm{cm}$$

Question 4

Which part of the human eye provides most of the refraction power?

Accepted Answer

Cornea

Question 5

If a camera's shutter speed is changed from $$1/500\ \mathrm{s} to$$ $$1/125\ \mathrm{s}$$, by what factor must the lens area be reduced to avoid overexposure?

Accepted Answer

$$1/4$$

Question 6

A compound microscope has an objective lens with $$f_o = 0.40\ \mathrm{cm}$$, an eyepiece with $$f_e = 3.0\ \mathrm{cm}$$, and a tube length $$L = 20.0\ \mathrm{cm}. If $$the near point $$N = 25\ \mathrm{cm}$$, what is the approximate angular magnification?

Accepted Answer

$$-420$$

Question 7

What is the refractive power in diopters for a lens with a focal length of $$-8.0\ \mathrm{cm}$$?

Accepted Answer

$$-12.5\ \mathrm{D}$$

Question 8

A telescope has an objective lens with $$f_o = 985\ \mathrm{mm}$$ and an eyepiece with $$f_e = 5.00\ \mathrm{mm}. $$What is the angular magnification of the telescope?

Accepted Answer

$$-197$$

Question 9

Which of the following best describes the effect of decreasing the aperture size in a camera?

Accepted Answer

Increases depth-of-field and reduces blur for out-of-focus points

Question 10

A magnifying glass has a focal length of $$9.5\ \mathrm{cm}. $$What is the angular magnification when used with a relaxed eye?

Accepted Answer

$$2.6$$

Question 11

In a two-lens system, two converging lenses each have $$f = 20\ \mathrm{mm}$$ and are separated by $$30\ \mathrm{mm}. An $$object is placed $$28\ \mathrm{mm} in $$front of the first lens. What is the final image distance from the second lens?

Accepted Answer

$$13\ \mathrm{mm}$$

Question 12

A farsighted person has a near point at $$75.0\ \mathrm{cm}. If $$glasses are worn $$2.0\ \mathrm{cm} in $$front of the eye, what focal length is needed for the glasses so the near point is corrected to $$25.0\ \mathrm{cm}$$?

Accepted Answer

$$33.6\ \mathrm{cm}$$

Question 13

What is the formula for the f-stop of a camera lens?

Accepted Answer

$$f	ext{-}stop = \frac{f}{D}$$

Question 14

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

Accepted Answer

The cornea provides most of the eye's refractive power.

Question 15

If the image formed by a camera lens is inverted and smaller than the object, where is the object located relative to the lens?

Accepted Answer

Farther than twice the focal length from the lens

Question 16

What is the maximum angular magnification obtainable by using a $$3.0\ \mathrm{cm}$$ eyepiece alone as a magnifying glass, with a near point of $$25\ \mathrm{cm}$$?

Accepted Answer

$$9.3$$

Question 17

A telescope has an objective lens of $$f_o = 985\ \mathrm{mm}$$ and an eyepiece of $$f_e = 5.00\ \mathrm{mm}. $$What is the approximate length of the telescope?

Accepted Answer

$$990\ \mathrm{mm}$$

Lecture 17

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