Kenneth, Spring; Keller, H. Ernst; Davidson, Michael W. "Microscope objectives". Olympus Microscopy Resource Center. Archived from the original on 1 November 2008. Retrieved 29 Oct 2008.
Kenneth, Spring; Keller, H. Ernst; Davidson, Michael W. "Microscope objectives". Olympus Microscopy Resource Center. Archived from the original on 1 November 2008. Retrieved 29 Oct 2008.