During his tenure at the School of Fine Arts in Budapest Lahner visited an art exhibition in Lausanne, Switzerland. Seeing for the first time the works of Delacroix, Van Gogh and Monet had a profound impact on the young artist. He decided shortly thereafter to move to Paris where he could study the modern masters.

Lahner arrived in Paris in 1924 and took up residence in the Latin Quarter. After a year he moved to Avenue Junot in Montmartre, where he lived until returning to the Left Bank in 1927 to reside in the Villa Seurat.

Like many artists before him, Lahner was entranced by the brilliant light of the Mediterranean coast. Throughout the 1920's he traveled to Sanary-sur-Mer, Saint Tropez and Saint-Paul-de-Vence, where he spent the summers painting seaside landscapes and villages.