![]() 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. Refractive optics in achromatic telescopes focus the wavelengths to which the eye is most sensitive, in the green portion of the spectrum. ![]() These out-of-focus red and blue images combine to form a purple color that appears as a halo around bright stars. 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.īecause 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. Purple halos around stars can be a problem when shooting with inexpensive camera lenses and telescopes. ![]()
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