This article discusses about schlieren methods which can draw hidden details in high-speed flow visualization. Mainly, two schlieren techniques are used, namely, inclined schlieren and focusing schlieren. These two techniques have been applied to visualize normal-shock–boundary-layer interaction in ducts. The paper explained the possibility to measure normal shock oscillation in spanwise/transverse direction. Identification of shock location across the duct span is also illustrated, using focusing schlieren. Further, the possibilities and limitations of focusing schlieren in high-speed flow visualization have been discussed.