Old 16th century portrait

Very old portrait dating from 1838 in the image of a man with a frank gaze. We will appreciate the details of precision and expression of the work there is no signature but we can imagine a quality of execution quite striking. The features of the face are impressive. The light is located on the face and contrasts with the darkness of the rest. On the back we can read ''j.letscher mekanikus'' It would seem that ''mekanikus'' is a German word. (mechanic) of boat...or others... The canvas is certainly damaged but it is very old.