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Physics 21
Fall, 2004
Solution to HW27
36
P21
The normal lens of a 35 mm camera has a fo
cal length of 50 mm.
Its aperture diameter varies from a
maximum of 25 mm (
f/
2) to a minimum of 3.0 mm (
16).
Determine the resolution limit set by diFraction for
2and
16. Specify as the number of lines per millimeter resolved
on the ±lm. Take
λ
= 500 nm.
²or a lens diameter
a
, the angular distance from the cen
ter of the diFraction pattern of a line to the ±rst zero will
be 1
.
22
λ/a
. Assuming the lens is focussed at in±nity, the
distance to the ±lm will be the focal length
f
, so the actual
distance will be 1
.
22
fλ/a
. This distance is the closest spac
ing of two justresolved lines. The number of lines per unit
length
N
resolvable on the ±lm will be the reciprocal of this
distance,
N
=
a
1
.
22
fλ
.
²or
f
=50mmand
λ
= 500 nm,
a
=25mm
⇒
820
/
mm
,a
=3mm
⇒
98
/
mm
.
36
P34
Missing orders occur for a diFraction grating when
a diFraction minimum coincides with an interference maxi
mum. Let
a
be the width of each slit and
d
the separation of
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This note was uploaded on 08/06/2008 for the course PHYS 21 taught by Professor Hickman during the Fall '07 term at Lehigh University .
 Fall '07
 Hickman
 Physics, Diffraction, Light

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