親子觀星會

https://www.cloudynights.com/topic/476781-m45-halo-trouble/

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Removing Purple Star Halos
https://www.skyandtelescope.com/astronomy-blogs/astrophotography-jerry-lodriguss/purple-star-halos-astrophotography/

Purple halos around stars can be a problem when shooting with inexpensive camera lenses and telescopes. They come about when refractive optics — optics that contain lenses — don’t focus blue and red wavelengths of light at the same place as the rest of the visual spectrum.

Because these wavelengths focus at different distances based on the refractive index of the glass, star images at red and blue wavelengths will be out of focus and appear larger than the in-focus star images in green light. These out-of-focus red and blue images combine to form a purple color that appears as a halo around bright stars.

Refractive optics in achromatic telescopes focus the wavelengths to which the eye is most sensitive, in the green portion of the spectrum. Because the eye is not as sensitive to the long red and short blue wavelengths, their lack of color correction is not as noticeable visually. But digital cameras will record these wavelengths, particularly in the long exposures common to deep-sky astrophotography.

https://kknews.cc/zh-tw/news/l9je9mz.html
消色差折射式望遠鏡

這種折射望遠鏡的物鏡，是由兩塊不同折光率的玻璃鏡片組成，之間有一個空氣薄層，以減少色差，使紅藍兩色的 影像聚在同一焦點上，在口徑小於100毫米時，這種設計非常有效。嚴格來說，這類鏡頭影像外圍仍有一個很淡紫色的光暈，尤其是在觀測明亮的天體和月球的邊緣的時候這種情況會比較明顯


原文網址：https://kknews.cc/news/l9je9mz.html

都是二次反射造成的  => HALO

那個東西只存在B通道

Flares on bright stars

https://www.cloudynights.com/topic/613747-flares-on-bright-stars/

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