APO: Apochromatic, one of the types of telescopes with the best image quality.
ED: It is a low dispersion lens. It usually refers to a two-piece refractor with one piece being ED. It is also the intermediate type between apo and general consumer.
Some astronomical telescopes are only equipped with APO lenses, and some are only equipped with ED lenses. Astronomical telescopes can meet both APO and ED lenses, so they are different.
Among them, APO (apochromatic) has a broader concept. APO lenses must be ED lenses. But conversely, ED lenses must be APO lenses. Obviously, the prices of the two are not at the same level, and APO lenses are much more expensive.
Extended information
The reasons why APO lenses are expensive:
1. The apochromatic materials used in APO lenses are expensive and costly.
2. It is difficult to process apochromatic materials used in APO lenses, and labor costs and machine shift costs are relatively high.
The above reasons make APO lenses expensive, so they are usually used on high-end lenses. In astronomical telescopes, the performance of APO lenses is also better.
APO lenses have become synonymous with high-end lenses. APO is the abbreviation of English Apochromatic, which means "apochromatic". The so-called fluorite lenses, AD glass, UD glass, and ED glass are, in the final analysis, special optical materials used to realize APO technology. ?
The reasons why ED lenses are cheap:
1. The production process of low-dispersion glass used for ED lenses is relatively simple, the raw materials are cheaper, and it can be processed to a greater extent for mass production.
2. The low-dispersion glass used for ED lenses cannot achieve apochromatic aberration and cannot eliminate the secondary spectrum, so its performance is equivalent to weaker.
The above reasons make APO lenses expensive, so they cannot be compared with APO technology. In astronomical telescopes, the performance of ED lenses is also excellent. The lenses are of high quality, with small spherical aberration and high color reproduction.
The purpose of producing ED lenses:
General optical lenses will be accompanied by greater light scattering, which is chromatic aberration, mainly due to different colors of visible light (red, blue, Green, etc.) have different wavelengths and have different refractive indexes through optical lenses, so they cannot converge on the same plane. Red light with a longer wavelength and blue light with a shorter wavelength can easily cause dispersion, which greatly affects the sharpness and color vividness of the image.
Through continuous experiments and tests, engineers have roughly decomposed the image color dispersion phenomenon produced by optical glass into "longitudinal chromatic aberration" - concentric circles of color bleeding and blurring will appear in the center of the focus. "Magnification chromatic aberration" - heterochromatic light spots are formed around the focused image, starting from the center and gradually expanding toward the edges. The longer the focal length of the lens (telephoto), the more obvious the chromatic aberration will be.
Early research found that natural fluorite has a unique ability to eliminate chromatic aberration, but natural fluorite crystals are too small and expensive to be used in the production of lenses.
Until the end of 1968, the Japanese company CANON pioneered the technology of artificially synthesizing large sheets of artificial fluorite (CaF2 calcium fluoride), and in 1969 launched the first lenses using fluorite lenses, the Canon FL-F300 F5.6 and FL-F500 F5.6, and in 1973, CANON launched the famous FL300 F2.8 fluorite lens.
Because the cost of synthetic fluorite lenses was too high, CANON later developed another alternative made of optical glass mixed with patented oxides, named low-dispersion lenses "UD-Ultra Dispersion" ” and the more advanced “Super UD” lens, a lens that mixed UD and fluorite lenses, creating the famous “L” lens legend for Canon in the next thirty years.
Baidu Encyclopedia—ED Lens
Baidu Encyclopedia—APO Telescope