...BioRender.com. Base Light Source Condenser and Diaphragm Stage Objective Lenses Focus Knobs (Fine and Coarse...by a) adjusting the aperture of the condenser diaphragm to limit the amount of light hitting the sample...the eyepiece comfortably. Then, close down the diaphragm and use the coarse focus adjustment knob (the ...in your field of view and then slowly open the diaphragm until the edges are just out of view. Pro-Tip ... the power of the light source by opening the diaphragm so that you can easily see your sample. Then use...