Perf14 - I'm glad you have decided to jump in with some engraved stamp images!
First, as for the 50c Admiral Nimitz USA definitive, Scott No. 1869, it was engraved
by Thomas R. Hipschen; I posted several other examples of his work on page 8 of this thread.
Louis S. Schofield, who was active at the BEP during the 1920s and 30s, engraved the vignette on the 2c George Rogers Clark USA issue, Scott No. 651. Here are images of more examples of Schofield's vignette engraving work, all issued
by the USA. These stamps were produced during Schofield's famous "blue" period...just kidding! I chose these four to show because I happen to really like 'em.

- nethryk
John Ericsson Memorial, Potomac Park, Washington, D.C., designed
by Clair Aubrey Huston after a c.1926 statue
by American sculptor James Earle Fraser (1876-1953) depicting Swedish-born American engineer and inventor John Ericsson, who helped to revolutionize military-maritime technology with his ironclad warship, the Monitor. The allegorical figure above Ericsson is "Vision." This stamp was issued on May 29, 1926, Scott No. 628. (Lettering: Frank Lamasure)

Globe and airplane, designed
by C.A. Huston and Alvin R. Meissner, and issued on December 12, 1928 to publicize the Civil Aeronautics Conference in Washington, D.C., Scott No. 650.

Myron's Discobolus, designed
by Victor S. McCloskey, Jr., and issued on June 15, 1932 to publicize the 10th Olympic Games, held in Los Angeles, California, Scott No. 719. (Lettering: Edward M. Hall)

Crater Lake, Oregon, designed
by V.S. McCloskey, Jr,. and issued on September 5, 1934 as one of ten stamps in the National Parks Year issue, Scott No. 745. (Lettering: Donald R. McLeod)
