Biomedical Engineering Reference
In-Depth Information
θ
θ
FIGURE 1.3
Minimum blur spot due to diffraction of light when
d
=
f
. Notice how a larger aperture D results in a smaller
blur spot.
is
1. 22λ/
D
, the diameter of the blur spot at the
half-power point, shown in
Figure 1.4
to be
λ/
D
,
is often of interest. The size of the blur spot is
what determines what is often called the
dif-
fraction limit
of an optical system; however,
keep in mind that the blur spot size may be
dominated by lens aberrations, discussed later.
The diffraction limit assumes the use of some
resolution criterion, such as the ones named
after Rayleigh and Sparrow
[7]
. Note that cer-
tain highly specialized techniques can result in
spatial resolution somewhat better than the
λ
λ
λ
Ratio of ( /
D
)
FIGURE 1.4
Cross-section of a normalized Airy disk.
