There are several ways to align the sight of the infrared thermal imager:

1. Internal focusing: Focusing is achieved by adjusting the distance between the objective lens and the eyepiece. The advantage of this method is that the structure is simple, and the disadvantage is that the accuracy is low.

2. External focusing: Focusing is achieved by adjusting the distance between the objective lens and the eyepiece and the inclination angle of the objective lens. The advantage of this method is high precision, but the disadvantage is that the structure is complex.

3. Autofocus: Focusing is achieved by means of laser or ultrasonic waves. The advantage of this method is high precision, but the disadvantage is that the structure is complex and the cost is high.

Hope the above information can help you solve the problem. Please feel free to let me know if there are any other questions.