ABERRATIONS 131
Current trends in microscopy are toward ever-increasing ranges of wavelengths with some
techniques spanning a factor of two to three in wavelength. In general, a microscope objective
will be well corrected for Seidel aberrations across wavelengths. Dispersion has a small effect
on these corrections. However, a microscope corrected for chromatic aberrations in the visible
may not be well corrected in the infrared or ultraviolet. For laser illumination at a single wave-
length not too far from the band over which the lens was designed, the major effect will be
a shift in focus. Comparison of sequential images taken at different wavelengths may require
an adjustment of the position of the objective to correct for this shift, and an