An optical imaging system for an ophthalmic laser beam delivery system, which includes a focusing objective including a plurality of lenses, a semi-transparent folding mirror disposed near an entrance of the focusing objective for reflecting a treatment laser beam into the focusing objective, a prism disposed adjacent a back surface of the folding mirror, the prism having a first, a second and a third surface, the second surface being disposed adjacent the back surface of the folding mirror, the prism being configured to reflect a light that has entered the second surface sequentially by the first surface and by the second surface toward the third surface to be output, a focusing lens module disposed adjacent the third surface of the prism to focus light output from the third surface of the prism, and an image sensor disposed to receive the light focused by the focusing lens module to form an image.