This path led him to Hamburg in 1768, where he restored paintings, and to Frankfurt am Main in 1769, where he found himself admitted into the workshop of Christian Georg Schütz the Elder.
His original plan of going to Utrecht was dashed when he gained entry into the studio of Johann Andreas Benjamin Nothnagel (1729-1804), where for several years he was active in the fields of landscape, horse, and genre painting.
Morgenstern remained active in his field until his old age; contemporary reports mention most of all, for a miniaturist, the extraordinary fact that he worked to the end without glasses.
His works often have, next to their artistic, immeasurable historic value as almost photographically exact representations of churches shortly before the turmoil of the French Revolution, which caused a secularization as well as a radical classical remodeling.
During his lifetime, Morgenstern's paintings, as Philipp Friedrich Gwinner noted in 1862, were "bought straight from the easel, as it were" for the best of prices, as often for local private collections as in foreign European countries.