In this thesis diraction by a rectangular aperture is inspected. Measured data is collected, using digital camera CMOS sensor, and compared with theoretically obtained results calculated using symbolic computation program Mathematica 11.0. Theoretical analysis done by Kirchho is based on usage of Green's function and Green's second identity in combination with scalar wave equation. With proper boundary conditions three diraction formulas were obtained - one of the goals was to inspect which of mentioned formulas provide best foresight. To provide suitable and complete theoretical results, incident wave -in this case laser beam- is modeled using Gaussian beam. Controlling incident eld four cases were inspected regarding geometry of object light is diracted by. We start with diraction by a straight edge where only variable parameter is edge-sensor distance. Controlling this parameter normal incidence diraction by a slit is inspected. In this way slit width was recalibrated. Knowing both, mentioned distance, and slit width inclined incidence diraction was examined. To justify obtained results geometric corrections had to be imported. In such way observing diraction patterns we can inspect geometry of slit edges. At last, one of the slit wings was on-axis displaced and diraction by a shifted slit was observed. Comparing experimental and theoretical results we can conclude that scalar theory provides satisfactory results compared to experimental results. However, to provide more accurate measurements more symmetric slit with smoother surface of the blades, to lower distortion of diraction patterns, is needed. Distortion is especially striking for small widths. Also, it is shown that for large inclinations at angle incidence is more accurately presented using theoretical implications for diraction by a shifted slit.