It is important to have the images of both the specimen and the field diaphragm in focus. This is not an adjustment which has to be made frequently on our microscopes but you should be aware that this adjustment can be made. Open the field diaphragm to just fill the field of view. The more you close or stop down the condenser diaphragm the more you will increase the contrast of the image. Steps 1-4 must be repeated each time you change objectives if you want to obtain the optimal image with each objective lens.
Illumination Remember there are two controls for the light source.
The lower the number the more yellow the light. Due to its longer wavelength, yellow light decreases the resolving power of the microscope compared to blue light which is produced at higher light intensities. However, it is also important for you to set a light intensity that is conformable for your eyes.