13 April] 1892 in Tartu) was a Baltic German geologist and explorer, who travelled in and contributed to the scientific understanding of Kamchatka.

Ditmar began studying agricultural science but after some time changed to mineralogy and geology under Otto Wilhelm Hermann von Abich and Hermann Martin Asmuss.

After having graduated university with a master's degree, Ditmar in 1846–1848 travelled Europe and among other things attended lectures at the Freiberg Mining Academy in present-day Germany.

[1][3] In 1855–1856, Ditmar also made a geographical survey trip in the area of the river Amur.

He returned to Livonia in 1856 and settled in his estate at Käru, and in 1858 married Wilhelmina Stackelberg.