usually to project the image into a digital camera for recording purposes. Eyepieces
usually magnify by 10since an eyepiece of higher magnification merely enlarges the
image with no improvement in resolution. There is an upper boundary to the useful
magnification of the collection of lenses in a microscope. For each objective lens the
magnification can be increased above a point where it is impossible to resolve any
more detail in the specimen. Any magnification above this point is often calledempty
magnification. The best way to improve magnification is to use a higher magnification
and higher NA objective lens. Should sufficient resolution not be achieved using the
light microscope, then it will be necessary to use the electron microscope (Section 4.6).
In addition to the human eye and photographic film there are two types of
electronic detectors employed on modern light microscopes. These are area detectors
that actual form an image directly, for examplevideo camerasandcharge-coupled
devices(CCDs). Alternatively, point detectors can be used to measure intensities in the
image; for examplephotomultiplier tubes (PMTs)andphotodiodes. Point detectors
are capable of producing images in scanning microscopy (Section 4.3).Stereomicroscopes
A second type of light microscope, thestereomicroscope, is used for the observation
of the surfaces of large specimens (Fig. 4.6). The microscope is used when 3DFig. 4.6A research-grade stereomicroscope. Note the light source is from the side, which can give
a shadow effect to the specimen; in this example a vial of fruit flies. The large objective lens above the
specimen can be rotated to zoom the image.107 4.2 The light microscope