The red film is plated on the telescope objective lens, which breaks through the concept limitation of the UV-coated film on the telescope over more than 100 years. In the past, most of the antireflection film is coated with Shan 4 MgF2 film, so that the surface of the coated lens is reduced, and the dim light appears to be "rustic". Now the red-coated lens is a band-pass high reflective film system, in the red part of the reflectivity is very high, so that the color of the lens coated with red, so that the entire objective lens is dazzling, with the purple-blue augmented lens to form a sharp contrast, to achieve a good appearance decorative effect, open up the new market of the telescope. However, the red-film telescope is not actually as magical as the merchant calls it, and this article compares the pros and cons of the
First, this appearance of "breakthrough" with the telescope users do not have a subjective function of the relationship. Some people think it's "cool", others think it's like a red-headed fly. If most of the telescope is red film, it looks really "rustic", especially in the eyes of foreigners. Because the red film objective lens is a band-pass membrane system, the objective lens band range is 400. This makes the entire telescope color reduction slightly blue. What the Observer saw was a refreshing scene that changed the traditional view of the violet-blue film telescope to make the field of sight yellow (which caused the observer to be disturbed after prolonged observation). In short, the red-film objective telescope makes the observer's chroma mentality optimal. In fact, 400nm has exceeded the human eye observation limit (only 555nm sensitivity of 0.04%), so in visible light, the red film is only a high pass, a large part of the red light reflected out, so that the loss of light, making the scene blue. As to whether the blue is suitable for observation, this is a color psychological problem, very complex. I personally feel that blue makes people nervous, because this represents the night (indeed, the dark vision of the human eye moves to the blue), while the red and yellow can give people a warm feeling.
Second, red film reflection red light is too strong, through the telescope to see white objects can be clearly felt blue, just like the people brought a pay tinted glasses. In addition, the blue film is a glass surface reflective rate of the lowest single layer coating, not intentionally blue, reflected blue light is limited, therefore, through the telescope to observe the "yellow" phenomenon is also very limited.
In fact, the reason why the Red Film telescope is popular is because of good selling, because most buyers don't know the reason. The reason is sales this can be said: "You see, the lens is red, so it is infrared telescope," so as to deceive most of the unknown truth. I myself have a 8x 21 red-film telescope, not because I was deceived, but at the time I couldn't buy a telescope that was not a red film. An inappropriate example: the fashionable suit in the past few years, but all are double row buckle. What do not know in the West Burbur Han Square, the suit is the formal occasion of the clothing, single row buckle only formal, but to get China, to "serve", single row buckle on the outdated, the earth! I have observed that the typical clothes that migrant workers work on are suits! That's why the red-film telescope is popular in China. In a few more decades, it will be a history and a joke.