What Is an Optical Bench?

The optical bench is a versatile optical instrument. The optical bench used for testing is equipped with independent components such as collimators, self-collimating telescopes, measuring microscopes, and holders on the rail base. They can be arranged and adjusted as required to perform multiple test tasks. The optical bench used for physical experiments consists of a guide rail, a sliding seat (optical bench), a light source, an adjustable slit, an image screen, and various holders. According to the needs of the experiment, additional optical components, such as lenses, prisms, and polarization The sheet and the like constitute an optical system. The length of the commonly used guide rail is 1-2m. There is a ruler on the guide rail and a positioning line on the sliding seat, which is convenient for determining the position of the optical element.

In optical measurement, there are many items to be measured, such as geometric characteristic parameters and optical characteristic parameters of optical parts; optical characteristic parameters of optical systems; aberration measurement and image quality evaluation of the system. These measurements can be performed on the optical bench.

1. Measurement of geometrical characteristics and optical characteristics of optical parts and components. For example, measuring the parallelism and angular error of flat optical parts, the double aberration of the roof prism, the minimum focal length of the glass plate and prism, the focal length of the lens or lens group, the top focal length, etc.

2. Measurement of optical characteristic parameters of optical system. For example, measuring the magnification, exit pupil diameter and exit pupil distance, visual acuity, parallax of telescope system, human pupil of photographic objective lens, etc.

3. Image quality evaluation of optical system. For example, the image quality is evaluated by the star point method and the resolution method; the geometric aberration is measured by the Hartman method and the focal plane method.

Therefore, the optical bench is one of the basic instruments in the optical laboratory, and it is also a general instrument in the production of optical parts and the debugging of optical systems.

The main body of the optical bench is a straight track, which has two types: a simple double-rod type and a general straight track type. The length of the track is generally 1 ~ 2m, the millimeter scale is engraved on it, and there are multiple sliding brackets that can be moved on the rail surface. A good performance optical bench should have a longer guide rail, better straightness, better coaxiality and smoothness of the slider bracket.

Combining various optical elements (lenses, mirrors, etc.) into a specific optical system. When using these optical systems for imaging, to obtain a good image, the concentric structure of the beam must be maintained, that is, the optical system is required to meet or approach ideal optics. The conditions of the system. In this way, when any object point in object space is imaged by the system, there must be a unique conjugate image point in image space, and it conforms to various theoretical calculation formulas. For this reason, to adjust the optical system on the optical bench, the following points must be satisfied:

1.Optical bench level

Adjust the level adjustment screw (with the help of a spirit level) at the bottom corner of the optical bench to level the optical bench.

Co-axial

Adjust the optical axis of each optical element in the optical system to make it coaxial. And make the imaging beam emitted by the object meet the requirements of paraxial rays.

3.Contour

Because each distance in the imaging formula refers to the distance on the coaxial axis of the optical system, to obtain the actual distance from the reading on the optical bench track, the optical axis of the optical system and the optical bench track The baselines are parallel-for short. Adjusting the coaxial contour of each component of the optical system is a basic requirement in optical experiments. It must be well grasped. General adjustment can be divided into two steps: coarse adjustment and fine adjustment.

(1) Coarse adjustment: first place the object, lens, image screen and other components on the optical bench, check and adjust the center of the object, lens and screen in order, so that the center of each component is approximately on the same line parallel to the guide rail And make the object plane, image screen plane and lens plane parallel to each other and perpendicular to the optical bench guide.

(2) Fine adjustment: adjustment based on imaging rules. For example, in the lens focal length measurement experiment (as shown in Figure 1 on the right), if the object and the observation screen are far away, there will be two different positions and when the lens is moved, and two large and small real images will be displayed on the screen. . If the center of the object is above the optical axis of the lens and the optical axis is substantially parallel to the guide, then when the lens is moved, the centers of the two large and small images will coincide. If the center of the object deviates from the optical axis or the guide rail is not parallel to the optical axis, then when the lens is moved, the center of the image no longer coincides between the two imaging times. At this time, it can be adjusted to the state of coaxial height according to the offset of the image center. (As in Figure 2 on the right), the center of the object P deviates below the optical axis of the lens, then the centers of the two large and small images P and P deviate from the optical axis and are located at P and P above the optical axis, respectively. The center P is closer to the axis.

The general adjustment method is to adjust the position of the light screen so that P coincides with the center of the screen when forming a small image, and adjust the height or left and right of the lens so that P is located at the center of the light screen. It can be adjusted. ^[2]