His major achievement at the time was the improvement of the achromatic microscope objective.

Also, it quickly loses vertical resolution when looking at large areas since the veritical sensitivity depends on the microscope objective in use.

The beam is typically focused by sending it through a microscope objective.

Typical biological microscope objectives are designed for use with No. 1.5 coverslips (0.17 mm thickness).

This can be realized if a microscopy like optics and a microscope objective is used.

Commonly, a microscope objective is used to collect the object wave front.

However, as the microscope objective is only used to collect light and not to form an image, it may be replaced by a simple lens.

If a slightly lower optical resolution is acceptable, the microscope objective may be entirely removed.

Musoptin.com, microscope objectives: as they were used by Robert Koch for his first photos of microorganisms (1877-1878)

There is one other possibility: increasing the numerical aperture of a normal microscope objective.