Page 206 - Algae

Working with Light 189

FIGURE 5.9 Diffraction of light from different width aperture; the effect increases with decreasing
aperture width.

most optical systems, such as photographic and video cameras, with a large a/l; but it is very
important in all microscopes, where diffraction limits the resolution that microscope can ultimately
achieve (a/l tends to zero). The resolution is the smallest distance between two points to discrimi-
nate them as separate.

FIELD INSTRUMENTS: USE AND APPLICATION
Almost all light in the natural environment originates from the Sun. Its spectral distribution is
similar to that of an efficient radiant surface known as a blackbody at a temperature of 5800 K,
which ranges from 100 to 9000 nm, (Figure 5.10).
In passing through the atmosphere, a small portion of this light is absorbed, and some is
scattered. Short wavelengths are strongly scattered, and ozone absorption effectively eliminates
wavelengths less than 300 nm. At longer wavelengths, water vapor, carbon dioxide, and oxygen
absorb light significantly at particular wavelengths, producing sharp dips in the spectrum. At
still-longer wavelengths, beyond 4000 nm, all objects in the environment become significant
sources of radiations, depending on their temperature, and surpass sunlight in intensity. These
characteristics of the environment restrict the range of electromagnetic radiation. Solar radiant