Flashcards in Lecture 3 - Lens Power Specification and Measurement Deck (9)
When the back side of a lens is being referenced with lensometry, what is being measure?
BVP. Back Vertex Power
If nothing comes into focus, with a lensometer, what should you do as your next step?
Turn both the power drum and cylinder axis
When using the lensometer, minus cylinder format power will be the _______ reading
Note: It will be the second reading
Why are glasses flipped around when a bifocal is being tested?
You will have less error due to the sphere addition
If the BVP is 060 degrees, what will be the FVP?
What is the formula for target movement?
X= lensometer target mvt. in meters
fs = std. lens focal length in meters
Fv = lens power in diopters
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 = 2.5 mm
x= (0.05)^2 (40)
x=.1m = 100 mm
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)
= 0.0096 m = 9.6 mm