Parfocal is the word that describes a microscope that remains in focus when the objective lenses are changed.
Explanation;
Parfocal means that when one objective lens is in focus, then the other objectives will also be in focus.
Parfocalling compound microscope objectives is a procedure which allows one to adjust each objective lens so that it will remain in relative focus with the other objective lenses on the microscope when switching from one magnifcation to the next.
A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. A planet's hydrosphere can be liquid, vapor, or ice. On Earth, liquid water exists on the surface in the form of oceans, lakes and rivers.