Opticalmicroscope

First part of this video is accessible and simple. https://www.youtube.com/watch?v=5MfZweoJ6A8 The part at the end about phase contrast is not how we set it up on our scopes.

Zeiss step-by-step video. https://www.youtube.com/watch?v=Qk8dbT-N1xw Cued to where you put the sample on the microscope. If you start earlier, DO NOT touch the lamp housing on any of our scopes as described earlier in the video. You may also ignore the last step of removing the eyepiece to adjust the iris diaphragm. For practical use, it may be set at the numerical aperture of the lens or open fully.

Criticalillumination

STEP 6 To increase contrast, slowly close the iris diaphram (the aperture inside the condenser) just until the image begins to get dark, then open it a smidge. It should be right on the edge of where it starts to decrease the instensity of the image.

When you put your first sample on the microscope, you need to focus on the cells and then align for Köhler illumination.

科勒照明

Two more highly recommended videos by Jennifer Waters and Ron Vale. Waters' video https://www.youtube.com/watch?v=ZRZ9_ov6Fak goes deep into how Köhler illumination works. Vale's video https://www.youtube.com/watch?v=P1Tb_sllWII is more of a step-by-step on a Nikon microscope.

Be careful when adjusting the condenser diaphragm.  Closing the condenser diaphram reduces resolution.  To maximize both contrast and resolution, close the diaphragm just to the point where the image begins to get dark and no further.   This position is especially important when using Nomarski optics.

Every time you use the microscope for transmitted light work, whether brightfield, phase or DIC, you must align the condenser lens to assure Koehler illumination is optimal.  If you fail to do this, you will have poor resolution, wacky contrast artifacts, and unevenly lit pictures.