Follow the filter combinations for the fluorochrome. The aperture iris diaphragm, field iris diaphragm or objective's iris diaphragm opening is not completely opened. Completely open the aperture iris diaphragm and objective's iris diaphragm openings, and open the field iris diaphragm opening until its image circumscribes the field of view. A cube unsuitable for the specimen is used. Change to a suitable cube.
Image is unclear, blurred or has insufficient contrast.
Objectives or filters are dirty. Wipe them clean. The exciter filter and barrier filter are incorrectly combined. Follow the filter combinations for the fluorochrome. The aperture iris diaphragm or field iris diaphragm opening is not opened correctly.