Make sure microscope is adjusted for Köhler illumination.
Be sure to focus through the oocyst a number of times while adjusting the prism to observe the internal morphology completely. The prism should be adjusted through the mid-point (or darkest) point to observe the structures with light cast from multiple directions.
Adjusting the amount of light using the stage diaphragm and light source rheostat helps by altering the contrasting appearance of the internal features of the organism.
Use placement of the DAPI stained nuclei to help distinguish placement of sporozoites.
Distinguishing between a sporozoite and convolutions of the cell wall, distinguishing sporozoite placement and identifying sporozoites takes hours of practice using fresh organisms. Don't get discouraged.
Try to consult with other experienced microscopists to verify structures observed. Comparing to photographs is also helpful.
When using DIC microscopy, the background color varies depending on the filters in place. Gray to blue is the typical color used.
Always use a clean microscope and the minimum amount of non-fluorescing immersion oil necessary to ensure proper contrast and resolution.