Prisms
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Prisms
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| Porro Prism | |
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Porro Prism system takes an image an reverses it. In the case of
binoculars, since the image created by the objective lens is in reverse, the
Porro prism system will reverted and have the same orientation as the
original object seen by the observer without a binocular.
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| Roof Prism | |
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The Roof Prism (Amici Prism) is a right-angle prism that generally has a 90
degree roof on the face opposite of the right angle. The prism will
invert the image left to right, and if form in a similar system as the Porro
prism system, it will also invert the image upside down, so doing exactly
what Porro prism would do that is orienting it look similar to the original
object seen by observer without a binocular
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| Total Internal Reflection | |
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Prisms naturally have total internal reflection as in Figure 3 is the angle
at which it hits the surface is greater than the critical angle. The
Critical angle is found by using Snell's law, which is i
= arcsin(sin(r/n)) where i is
the incidence angle, and r is the
refraction angle and n is the index of
refraction for crown glass which is 1.52 (Note: the index of refraction
outside the prism is 1 since its air). So at the critical angle our r
= 90 degrees therefore i roughly equals to
41.14 degrees. But since the i at
which the ray hits the surface is 45 degrees therefore it is greater than
41.14, therefore it has total internal reflection.
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