section A: ol Flashcards
How to find power
n/f
different n available
1 =m
100=cm
1000=m
how to find combination
turn all f into F
add up F’s ( because focus lengths are not additive)
100/F = Total f cm
finding power with radius
F1 = (n-1) / r1
F2 =(1-n) / r2
n is is either front of back depending where the surface is
finding radius
R1 = (n-1) / F1 R2 = (1-n) / F2
Definition of lenses
lens is aways transparent optical media bounded by two polished surfaces, at least one must be curved
used to cut out radiation
Optical media are:
natural occurring material, glass and plastic
Dioptre
unit for a focal power is Dioptre
finding power with focal
F = 1/focal length = Fm
how to find total lens power
F = F1 + F2
what are quarter steps
-1.00 . -0.75 . -0.50 . -0.25
What are 0.12 steps
0.12 . 0.24 . 0.37
what is a flat form/plano confex/ Plano concave
Plano concave = F1 = infinity f2 = +.... Plano Convex F1 - infinity F2 = -...
Bi convex lens?
F1 = +…
F2 =+…
both plus
bi concave is opposite
Meniscus lens?
F1 = +... F2 = -...
how to work out sign for a radius
From front surface to centre = positive
from back surface to centre = negative
How to transpose from cross cyl to sphere cyl
Choose a cyl to make phere
use the axis where cyl was not chosen
how much is takes to get to the other cyl not chose =cyl
+3.00 x 180 / +2.00 x 90
= +3.00/ -1.00 x 90
or
= +2.00/ +1.00 x 180
how to relate a rx combination
Transpose so at least 2 matching section of axis
then add each section together
then the remaining together = replacement rx
what is minimum plate thickness
the thickness of a flat pale of glass from which the lens can be made
