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The field of view and the viewing angle of the medical rigid endoscope

The field of view and the viewing angle of the medical rigid endoscope are two very important optical performance parameters, which will directly affect the position and range of the observation object when the medical rigid endoscope is used. The measurement methods of these two optical parameters are introduced below.

First, explain the definition of the angle of view and the angle of view.

The field angle refers to the maximum range that the endoscope can observe at the same time, that is, the cone angle value with the vertex at the end of the endoscope lens, and the unit is degree. Usually the field of view of the 2.7mm～3.0mm endoscope is between 60～80 degrees. The field angle of 4.0mm endoscope is between 70 and 100 degrees, and the field angle of other endoscopes is between 50 and 70 degrees. The field of view of some ultra-wide-angle endoscopes can reach between 100 and 120 degrees, but the distortion is relatively large, and the observed objects will appear basketball-like shapes.

The viewing angle refers to the angle between the geometric axis of the tip end of the insertion part of the endoscope and the optical axis of the objective lens at the front end of the endoscope. Endoscopes are divided into direct view, squint and side view according to the observation direction. The common viewing angles are 0°, 6°12°25°30°45°70°90° and 110°.

Second: Rigid endoscope (Medical telescope) field of view and direction of view angle measurement accuracy requirements and tools needed.

Measurement accuracy requirements:
 
The minimum allowable accuracy of measuring the angle of view: ±5% of the reading of the rigid tube endoscope;
 
The minimum allowable accuracy of measuring the viewing angle: the rigid tube endoscope reads as ±3°
 
The optical bench, or similar equipment, can support the optical endoscope for testing, and can adjust the center axis of the field of view to coincide with the center of the measurement target. The end face of the endoscope lens is perpendicular to the angled concentric circle measurement center point. Measure the angle of view at 50±0.2mm (this method is the test method described in the national standard), and the test gauge is shown in the figure below.
 
Field of view and direction of view angle measurement map: is a set of concentric circles in degrees. The diameter of the concentric circle is calculated when the object distance is 50mm. The calculation formula is as follows: D=100tan(β/2)
 
Among them: D refers to the outer diameter of the concentric circles corresponding to a certain field of view angle; β refers to the field of view angle.
 
Finally, after the measurement tool is ready, we can start our measurement. The measurement steps are as follows


1) Mount the hard tube endoscope to be measured on the measuring device (fixture), and ensure that the center of the front end of the endoscope is 50±0.2mm from the center of the measurement icon;
 
2) Use the endoscope to connect the camera system to observe, and adjust the scale dial and height adjustment mechanism to make the center of the endoscope and the center of the measurement icon coaxial, even if the outer circle of the endoscope's field of view is coaxial with the measurement icon;
 
3) Read the nominal reading of the largest visible circle, which is the angle of the endoscope's field of view. The scale of the position where the scale disc rotates is the angle of the viewing angle of the endoscope. If it is not circular, take the reading of the largest circle in the visible part.
 
Although this is an ordinary test, a certain amount of professional technology and equipment is required, and the test is generally commissioned.