Lens Thickness

s=r- sqr(r² - y²)

accurate sag formula

s=y²/2r

approximate sag formula

s1-s2+ET

CT for a meniscus lens =

chord diameter /2

y=

(n-1)/F

r=

0

knife edged thickness means there is _____ thickness

middle of the edged shape

if there is no lens decentration, where is the OC?

center

where is a plus lens thickest?

closest

for a plus lens, the edge thickness will be greatest for edge ________ to the OC of the lens

edges

where is a minus lens thickest?

farthest

for a minus lens, the edge thickness will be greatest for the edge _________ from the OC of the lens

no

is the OC normally in the center of the lens after edging?

ED+(A+DBL-distance PD)

chord diameter=

K(F) + (ET or CT) + P/2

estimated center or edge thickness =

constant

what is “K”?

prism power

what is “P”?

0.7

if ED=50, K=

1.0

if ED=58, K=

the same

the center of a knife-edge plus lens & the edge of an infinitely thin minus lens have the same center thickness as long as the diameters and curvatures are _______

increases

as plus lens blank size increases, CT _______ rapidly

frame size & location of OC

the lens diameter needed to find the correct sag value depends on what 2 things?

50-58

the constant K in thickness estimation can be used for PDs of _______