A simple microscope is a
microscope that uses a single lens, or a set of lenses in close proximity, to enlarge an object
through angular magnification alone, giving the viewer an erect
enlarged virtual image. The image is erect, and if more than
one lens is used, the virtual image of the first is simply enlarged,
unlike in a compound microscope where the second set of lenses focuses
on the projected real image and the resulting image is inverted unless
a special image-erecting system is used. This type of microscope is
relatively limited to low to medium power magnification before
aberrations limit its usefulness. Van Leeuwoenhoek's most powerful
simple microscope magnified 250X whereas compound microscopes easily
reach 600X and with oil immersion 1200X or even more.
STOPS or PATCH STOPS:
Patch stops, or simply stops, are solid disks which block the central light rays of a condenser or light source. They are usually supported by a
spider frame with two or three struts, which fits into the swing-out filter holder of a condenser. Simple stops can allow dark ground illumination at the lower powers, but for high power dark ground illumination, a more sophisticated system is required. Depending on the condenser, the swing-out filter holder could have different diameters, hence the support of the stops was made in different diameter to fit the condensers in question.