Frederick Orthlieb (1945?-) is a mechanical engineer, professor, and tradesperson who has rehabilitated, upgraded, and modernized historical telescopes. While the telescopes are obsolete for current research work, after rehabilitation they are capable of productive and effective use for familiarization, secondary and higher education, and institutional and public outreach.

Orthlieb received his undergraduate and master's degrees from the Massachusetts Institute of Technology (MIT) in 1968 and his doctorate from Carnegie Mellon University (CMU) in 1974, all in mechanical engineering.

In 1975, Orthlieb began teaching engineering at Swarthmore College; he served as department chair from 1992 to 1998. He was named the Isaiah V. Williamson Professor of Civil & Mechanical Engineering in 1999. He retired in 2009.

Orthlieb was also the program evaluation visitor for the Engineering Accreditation Commission of ABET, Inc.; president of Heath Assured Systems, LLC; and chief engineer at Ray Museum Studios.

He began working with telescopes in 2005; significant projects include the 1931 Zeiss Urania refractor at the Franklin Institute's Bloom Observatory and the 1887 10-inch Clark refracting telescope at Bucknell University.