, a thin prism, Dm  is also very small, and
we get
(
)
21
/2
sin[(
)/2]
sin[
/2]
/2
m
m
A
D
A
D
n
A
A
+
+
=
≃
Dm = (n21–1)A
It implies that, thin prisms do not deviate light much 9 7  OPTICAL INSTRUMENTS
A number of optical devices and instruments have been designed utilising
reflecting and refracting properties of mirrors, lenses and prisms Periscope, kaleidoscope, binoculars, telescopes, microscopes are some
examples of optical devices and instruments that are in common use