Direct light will destroy the image presented in the telescope. In order to enhance the visual image, the lens and prism need to be coated with a polarizing film. In general, the single-layer antireflection coating of the visual telescope has the best anti-reflection effect on a yellow and green light with a wavelength of 5500 angstroms, because the human eye is most sensitive to this wavelength. So it reflects more blue and red light. Multi-layer coated lenses are light green or dark purple, such as the coating of a camera lens. Single-layer films that are plated too thick will look green.
Some binoculars will have a lens coating mark to indicate the optical quality of the binoculars. The types of coating are as follows:
Coated Optics (coating): It is the lowest level of antireflection coating. It only means that at least one optical surface is coated with a single-layer anti-reflection coating, usually on the outer surfaces of the two objective lenses and eyepieces, while the inner lenses and prisms are not coated.
Fully Coated (full surface coating): All lenses and prisms are coated with a single layer, but if optical plastic lenses are used in the eyepieces, the plastic lenses may not be coated.
Multi-Coated (multi-layer coating): at least one optical surface is coated with a multi-layer antireflection coating, other optical surfaces may be coated with a single layer coating, or may not be coated at all; usually only on the outer surface of the two objective lenses and the eyepiece Plating multilayer film.
Fully Multi-Coated (multi-layer all-optical surface coating): All lenses and prisms are coated with anti-reflection coating. Some manufacturers have coated multi-layer coatings on all optical surfaces, while others only have multiple coatings on some optical surfaces. The other surface is still coated with a single-layer film”.
The more common ones in China are broadband green film, decorative green film, red film, and blue film, as well as purple film and yellow film, etc.:
Broadband green film: It is also called antireflection green film in some places. It is currently one of the best coatings in the country. Observing from different angles will show different color bands (this is the performance of multi-layer coating), and the image is clear High, the color reproduction is also good
Red film: Generally only used for red dots, this one is more versatile and has no characteristics.
Blue film: It is the most widely used coating method in China. Compared with the broadband green film, it is slightly yellow and dark. The blue film is also layered. Some are coated with three layers, some are coated with five layers, and the worse is only one layer.
Decorative green film: This is very unethical. The color is very similar to the antireflection green film, but the optical performance is not flattering. The easier way to identify is that the decorative green film is very reflective, while the broadband green film is very light.
All in all, good lenses and coatings are very light, and the overall light transmittance can be about 85%-90%. If the inner lens also uses coated lenses, the overall light transmittance can reach about 93%, in order to achieve For higher light transmittance, there is also an internal lens coating method to improve optical performance, making the overall light transmittance reach 93%-95%.