Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.
Resolution and Diffraction Gratings
- Diffraction "blurs" images together, and places a limit on the
finest details one may distinguish
- If one looks at two objects through a rectangular slit
using light of wavelength lambda, then the two objects
will appear to blur together when their projected angular
separation is
lambda
sin (theta) = -------------
width of slit
- A similar formula describes the smallest angular separation at which
two point sources of light (like headlights, or stars) may
be distinguished when one looks through a circular aperture:
lambda
sin (theta) = 1.22 -------------------
diameter of aperture
- One can increase one's ability to distinguish fine detail by
increasing the aperture through which one is looking, or
by using light of shorter wavelengths.
- A diffraction grating is a device with many, many parallel slits
very close together. When light passes through a diffraction
grating, it is dispersed into a spectrum.
- Light of wavelength lambda which passes through a diffraction
grating of spacing d will create a bright spot at angles
lambda
sin(theta) = N ------ for N = 0, 1, 2, 3, ....
d
- A diffraction grating disperses light into a rainbow, like a prism;
but the order of the colors is opposite for the two devices.
A prism throws blue light most away from the center;
a grating throws red light most away from the center.
- One can use diffraction gratings to stretch light into spectra,
then identify different chemical elements and compounds from
the patterns of light in the spectra.
Viewgraph 1
Viewgraph 2
Viewgraph 3
Painter Georges Seurat knew the resolution limit of the human eye
and the distance at which spectators typically viewed his work.
He used tiny little dots of paint which are just at the limit
of resolution to create "A Sunday on La Grande Jatte".
Viewgraph 4
Viewgraph 5
Viewgraph 6
Viewgraph 7
Viewgraph 8
Viewgraph 9
Viewgraph 10
Viewgraph 11
Viewgraph 12
Viewgraph 13
Viewgraph 14
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.