Fig. 1. Schematic of experimental setup

Fig. 2. Light deflection diagram

Fig. 3. Image of the light source at the knife edge

Fig. 4. Experimental setup

Fig. 5. Images with hot air gun disturbance. (a) T=200 ℃; (b) T=300 ℃

Fig. 6. Undisturbed image after brightness processing

Fig. 7. Disturbed image after brightness processing

Fig. 8. Number of stripes with different schlieren lens focal lengths

Fig. 9. Simulated images. (a) n=0.6417, f3=200 mm; (b) n=1.000051, f3=200 mm