 His nicest motive were birches, between the years 1905 until 1907 he made a cycle of landscape photographies with birches, which were made in gum bichromate procedure, this was his favourite procedure which allowed him the most experimenting and acquired him an award in Oslo in 1908.Berthold liked to photograph farmers when they were working.Farmer who was bent down to reach the earth in his specific gestures, showed the type of a person connected with the past and time, when people were still more connected with the nature, when they were fully dependent on it.