The design and testing of different optical heads were performed to evaluate the pitch deviation of a diffrac-tion scale grating with a small diffraction angle. Based on the proposed pitch deviation evaluation method employing optical angle sensors based on laser au-tocollimation, a modified optical head with position -sensitive detectors (PSDs) is first designed and con-structed by following the conventional optical config-uration. Owing to the small angle of diffraction of the first-order diffracted beams, the modified optical head has a large working distance, resulting in poor sensor stability. Therefore, a novel and compact optical head employing a pair of small prisms is designed and de-veloped to shorten the working distance of the opti-cal head. An additional modification was also made to the developed compact optical head in such a way that collimator objectives (COs) in the laser autocollima-tion units are removed to improve the sensor sensitiv-ity. Experimental comparisons were conducted using the three types of optical heads to verify the feasibility of the developed optical angle sensor with PSDs.