Lecture 3 - Lens Power Specification and Measurement Flashcards Preview

Optics 2 - Final > Lecture 3 - Lens Power Specification and Measurement > Flashcards

Flashcards in Lecture 3 - Lens Power Specification and Measurement Deck (9)
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1

When the back side of a lens is being referenced with lensometry, what is being measure?

BVP. Back Vertex Power

2

If nothing comes into focus, with a lensometer, what should you do as your next step?

Turn both the power drum and cylinder axis

3

When using the lensometer, minus cylinder format power will be the _______ reading

First.
Note: It will be the second reading

4

Why are glasses flipped around when a bifocal is being tested?

You will have less error due to the sphere addition

5

If the BVP is 060 degrees, what will be the FVP?

120 degrees.

6

What is the formula for target movement?

X=fs^2 (Fv)

X= lensometer target mvt. in meters
fs = std. lens focal length in meters
Fv = lens power in diopters

7

1) A lensometer has a +20D std lens. How far does the target move in measuring a +1.00D lens?

2) If the same lensometer power drum moves from +20 D to -20D reading, how far would the target move?

x=(0.05)^2 (1)
x = 2.5 mm

x= (0.05)^2 (40)
x=.1m = 100 mm

8

Given an Rx +3.00 - 6.00 x 180. How far does the target move between the 2 meridians if the std. lens is +25 D.?

x = fs2 (Fv)
= (0.04)2(?)
= (0.04)2(6)
= 0.0096 m = 9.6 mm

9

-A lensometer with a +20 D std. lens.

-The single line focuses 5 mm behind the plano position.

-The triple line focuses 6.25 mm in front of the plano position.

-The axis indicator reads 45° What is the Rx?

x = fs2 (Fv)
-.005 = (0.05)2 (Fv)
-2.00 = Fv

x = fs2 (Fv)
.00625 = (0.05)2 (Fv)
+2.50 = Fv

+2.50 -2.00 x 135
Note: The axis was rotated from its original position 45 to 135