4-4-2 using the aperture diaphragm
（
fig.25
）
◎ When in the bright field observation, the aperture diaphragm control the numerical
aperture of the illumination system. Only when the numerical aperture of the objective
and the illumination system being matching, you can obtain the higher image resolution
and contrast, and the increased depth of field, too.
● To recognize the aperture diaphragm, you could remove the eyepiece if necessary. ( you
also could insert in the center telescope )then looked into the viewing tube, you might
see a field of view like the figure shown. The proportion could be changed by dialing
the aperture adjustment lever according your need. (①is the image of the aperture
diaphragm , ② is the edge of the objective)
● Generally, when observing the chromatic specimen, you need to set the size of the
condenser aperture diaphragm at 70%～80% of the numerical aperture which marked in the
objective. but if observing the bacterium specimen which not colored, you could turn
the aperture diaphragm lever at the direction of“
”(clockwise).
