"Following early experiments on 8mm between 1953 and 1957, [Kren] made his first 16mm film VERSUCH MIT SYNTHETISCHEM TON (1957), including a drawn soundtrack beginning to develop the notions of formal relationships between simple images. But his next three films, made between then and 1961, showed the systematic direction of his work most clearly: 48 KOPFE AUS DEM SZONDI TEST (1960) and BAUME IM HERBST (1960) being shot according to system, and MAUERN-POSITIV-NEGATIV UND WEG (1961) being edited that way. It is also evident in these films and is confirmed in his next, FENSTERGUCKER, ABFALL, ETC. (1962), that even if Kren rejected poetic or narrative intention, the images of his work were in no way neutral, arbitrary or convenient fillers for a mathematical system." - Malcolm Le Grice, Abstract Film and Beyond, 1977

"[I]n this concentrationary universe, no one's his own self, everyone's everyone and nothing. Ruthlessly executed, the formal idea becomes a gruesome philosophical jest." - Raymond Durgnat, International Times, 1966