Nominal Power, Focal Length, Saggital Depth, Thick Lens Power

Question 1

Sagittal Depth is the straight line distance between the back surface of a lens at its vault (where the curve is the deepest) and the chord diameter (the straight curve of the lens)

Answer 1

True

Question 2

If the radius of a surface remains the same and the diameter changes, the thickness will change but the sag depth will remain the same.

Answer 2

False

Question 3

If the radius of a surface is reduced and the diameter remains the same, the thickness will be reduced.

Answer 3

True

Question 4

If the sagittal depth remains the same, and the diameter increases, the surface will become flatter.

Answer 4

True

Question 5

If the sagittal depth remains the same, and the diameter increases, the surface will become flatter.

Answer 5

True

Question 6

What is the formula to find the focal power of a lens?

Answer 6

D = 1/f, where f is in meters. D is dioptric power, f is focal length

Question 7

If f is measured in inches, then what is the formula to find the dioptric power of the lens?

Answer 7

D = 39.37/f

Question 8

What is the formula for nominal power?

Answer 8

D = D1 + D2

Question 9

What is the thick lens/back vertex formula, and what does each variable stand for?

Answer 9

D = D1 + D2 + (t/n x D1^2)
D = effective, vertex, or lensometer power
D1 = true power of front curve
D2 = true power of back curve
t = thickness of lens in meters
n = index of refraction