Page 61 - PowerPoint 演示文稿

Prisms 51

There is a mathematical solution to compounding prisms. The formula
is:

PR =
Where, PR = Single resultant prism
PV = Prism vertical
PH = Prism horizontal

Putting the values from the previous example:

PR = 3  4 2
2
PR = 9  16

PR = 25
PR = 5Δ
Now to obtain the base setting use:

tan θ =

tan θ =

tan θ = 37°
This needs to be converted to standard notation by subtracting from
180° (180-37=143).
Therefore, the answer is 143°.

PRISM AND LENS DECENTRATION
The general theory is if the lens power is 1.00D and we decenter the lens by
10 mm, it produces 1Δ prism or if the lens power is 10.00D and we decenter
it by 1 mm, it also produces 1Δ prism. This is constant. The equation is:

(i) d =

(ii) P =

Where, d = Decentration in mm
D= Dioptre or lens power
P = Prism degree
The required prism degree can be found out with the help of above equation.
Now while grinding or surfacing, the lens prisms can be produced by
keeping the edge difference for which the equation is:
Prism × Size of lens × 0.019 = Edge difference.