This should give the best contrast. This should be done for each objective for critical viewing. In practice, you can experiment with this while viewing a specimen and adjust it without removing the ocular. Closing the aperture iris increases contrast and depth of field up to a point. If it is closed too much, a flat indistinct image results.
Closure also diminishes the color of the specimen.
Once you have achieved what you think gives the best image quality, remove one of the oculars and see how much of the field is occluded. While these procedures may seem tedious, they will become routine as you progress and they are essential if you want to get good photographic results. I haven't used Print Film very much. However, Fuji Color or Kodak ASA 100 films should be adequate. You can scan the prints and the negatives which can be an advantage.