13. How does the focal length of a lens influence the size of an image and its m

Question

13. How does the focal length of a lens influence the size of an image and its magnification?

14. What is an f-number? How does it change with differing focal length and/or diameter of a lens?

15. How does changing an f-number affect the depth of field?

16. How does f-number depend on the area of a lens?

17. How are f-numbers arranged on the f-number sequence?

18. How do we combine f-number with the shutter speed to influence the amount of light entering a lens?

19. What is the exposure, and how does it depend on the intensity of light, exposure time and area of the lens? (Exposure = intensity × area × exposure time)

Explanation / Answer

13. The focal length of a lens can be determined with the relationship:

     f = h / tan(Theta)

14. In optics, the f-number of an optical system is the ratio of the lens's focal length to the diameter of the entrance pupil. It is a dimensionless number that is a quantitative measure of lens speed, and an important concept in photography. The number is commonly notated using a hooked f,

i.e. f/N,

where N is the f-number.

19.exposure is the amount of light per unit area.Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.

Exposure = Intensity x Time (E = I x T)

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