A microscope comprises a microscope objective, a camera and an imaging optical system for imaging an object through the objective to the camera along a first optical path. A projection optical system is provided for projecting a test image onto the object through the objective, and the imaging optical system is configured to image the projected test image from the object to the camera through the objective and along at least part of the first optical path. A focus adjustment system is provided for focusing the test image at the camera. Using the same objective and the same camera for both imaging and focusing allows reduction of the cost of the microscope in comparison with known microscopes that provide separate focusing systems.