(1) A condition that needs to be met when the convex lens becomes a real image

　　 (2) Conjugate imaging means that the object distance and the image distance can be interchanged. In the two cases, it is zoomed in and zoomed out. Inverted real image

　　 Looking through a convex lens at a timepiece outside of the double focal length, the image of the second hand still rotates clockwise, because it is an inverted real image, which is still the normal direction when viewed backwards. It is still turning clockwise.

(1) The lens is represented by the lens symbol (a line segment has two V-shaped signs at both ends), the main optical axis is drawn, and the optical center and focal point are marked according to the three special rays of the lens. At the intersection of two refracted rays (generally the rays passing through the optical center and the rays parallel to the main optical axis are better), the characteristics of the image formed by the lens (such as virtual reality, size, front and back, etc.) can be obtained.

(Optical lens 2). When the lens is imaging, all the rays of light emitted from each point on the object that hit the lens are imaged at the same position, blocking a part, and does not affect the other rays of the lens. Imaging, so you can still see the complete image, but because the light hitting the image is reduced, the brightness of the image on the screen will become darker.

　　The role of the lens in the optical system is: focusing, collimating, imaging, the lens usually needs to be coated with antireflection coating to reduce the reflection of the lens surface, which can reduce the loss of light energy , The imaging is clearer.

　　 lens is an optical element made of transparent materials (such as glass, crystal, etc.), which will affect the curvature of the wavefront of light. It is a device that can converge or disperse light, and the resulting images have real and virtual images. It is widely used in various fields such as security, car wearing, digital camera, laser, optical instrument and so on.

　　Check whether the printing point of the instrument is the true optical center of the optical lens at any time

　　 After verification, the general instrument will print The error between the center point printed by the device and the optical axis of the instrument is within the specified range. However, for some portable instruments, the printing device is quite rough, or the printing device is used frequently or improperly. What's more, some instruments have not been verified for a long time. These may cause the printing center point to be inconsistent with the optical axis of the instrument and exceed the specified requirements.

　　Here we recommend that the user can use trial case lenses to verify, the method is to put a ten 15D refraction lens on the instrument, turn the focusing handwheel to show a clear target score Scribe the image, move the refraction lens to zero the prism, and press the printing device.

　　 Turn the lens 180 degrees again, repeat the above operation, when the prism power is zero, press the printing device again, then use a ruler to measure the focus lens of the two printed dots If the distance is less than 0.4mm, it is qualified. Otherwise, you should go to the measurement department to make adjustments.

　　In actual work, it is recommended to adopt this method: place the inspected lens on the instrument, and according to the above method, after two alignments in the 0 and 180 degree directions , Print out two points, the center point of these two points is the actual optical center point of the lens.

　　 Place the tested lens or spectacles correctly, so that the vertex of the eye square surface of the lens is in contact with the lens support ring on the instrument. The measured lens power actually refers to the tested lens. The back vertex power value of the lens. The so-called back vertex power value refers to the reciprocal of the distance from the apex of the eye side surface of the lens to the eye side focal point (that is, the back vertex focal length). The unit is diopter, which is represented by the symbol 'D

　　The design of various focal meters is also based on this concept. For all aspheric lenses, when we measure lenses (or glasses), we must make the concave surface of the lens contact the lens support ring of the instrument, otherwise, if the lens is placed down, the measured value will not be the back vertex value. , Especially for height value lenses, the difference is even greater. This is not clearly stated in the general instrument manual. In addition, when measuring astigmatism glasses, the lens ring must be close to the positioning plate of the instrument.

　　We believe that the following points should be paid attention to when reading:

　　(1) First of all, the '0' of the instrument Whether the point is correct, it must be corrected if there is an error.

　　(2) When turning the focusing handwheel, it must be adjusted from a single direction to clear to eliminate the gap caused by the gap between the gear and the rack or the loose rotation of the reading drum. The error.

　　(3) When focusing, only check whether the image of the visual marking reticle is clear, and do not focus on the reading value in the reading window when focusing, so as to avoid 'preemptiveness' .