Worksheet 4: Focal Length Formula.
Diopters, Lens surfaces.
Lens characteristics.

Focal Length

  1. What is the focal length in meters of a +4.50D lens?

    2. m (Round to three decimal places.)
    .
  2. What is the focal length in mm of a -6.25D lens?

    3. mm (Round to nearest mm.)
    .
  3. What is the focal length in inches of a +4.00D lens?

    4. in (Round to nearest inch.)
    .
  4. What is the focal length in cm for a -9.37D lens?

    5. cm (Round to nearest cm.)
    .
  5. What is the dioptric power of a lens that has a focal length of +1.149 m?

    6. D (Round to nearest eighth D.)
    .
  6. What is the dioptric power of a lens that has a virtual focal point 200 mm away from the lens?

    7. D (Round to nearest eighth D.)
    .
  7. A normal reading distance is 16 inches. What lens would have a positive 16 in focal length?

    8. D (Round to nearest eighth D.)
    .
  8. What power lens has a negative focal length of 50 cm?

    9. D (Round to nearest eighth D.)

    Lens Surfaces

  9. The lens shown to the right has two surfaces. They are:

    10. both flat
    both concave
    both convex
    one convex and one concave
    .
  10. This lens is a

    11. flat design
    bent design
    .
  11. The lens shown to the right is :

    12. equi-concave
    equi-convex
    bi-concave
    bi-convex
    .
  12. This lens is a

    13. flat design
    bent design
    .
  13. The lens shown to the right has two surfaces. They are:

    14. both flat
    both concave
    both convex
    one convex and one concave
    .
  14. This lens is a

    15. flat design
    bent design

    Lens Characteristics

  15. What type lens converges parallel incident rays?

    16. plus lens
    minus lens
    both plus and minus lens
    .
  16. What type lens is thinner the center and thicker on the edges?

    17. plus lens
    minus lens
    both plus and minus
    .
  17. What type lens gives a real image?

    18. plus lens
    minus lens
    both plus and minus
    .
  18. What type lens gives a virtual image?

    19. plus lens
    minus lens
    both plus and minus
    .
  19. What type lens shows with motion?

    20. plus lens
    minus lens
    both plus and minus
    .
  20. What type lens becomes stronger as it moves away from the eye?

    21. plus lens
    minus lens
    both plus and minus
    .
  21. What type lens shows minification?

    22. plus lens
    minus lens
    both plus and minus
    .
  22. What type lens becomes stronger as it moves toward the eye?

    23. plus lens
    minus lens
    both plus and minus
Click the submit button to see my answers. Contact me if you have any questions about this lesson. Make sure that you have completed this worksheet before you go on to the weekly BlackBoard quiz.

Close the window (click the little x in the upper right-hand corner) if you came here directly from the assignment page.


Textbooks:
Brooks & Borish, Systems for Ophthalmic Dispensing, 2nd Ed, Butterworth-Heinemann, 1996
Stoner, Optical Formulas Tutorial, Butterworth-Heinemann, 1997

Copyright 1998 - 2001, Ellen Stoner, MALS, ABOM, NCLC
Registered students may print one copy for study purposes.