A refractor is a telescope with a lens in the front that captures the incoming light and converges it to a focal point by refraction. There are roughly two types of refractor telescopes; achromatic and apochromatic refractors.
Achromatic refractors have a dual lens element design. Achromats can suffer from so-called chromatic aberration which looks like small rainbows around bright objects like the moon and bright stars. This is because this system is unable to bring all colors of the spectrum at the exact same point in focus. Note: this is neither good nor bad; it is a natural feature of this design. Achromatic refractors are generally fine for visual observations with limited magnifications. They are less suitable for photography.
Apochromatic refractors have an lens design that consists of three or more elements. This makes it possible for all the light to be in focus at exactly the same point. This makes it a color-corrected system. Apochromats are well suited for visual observations and astrophotography.
All refractor telescopes have a curved focal plane. Visually this is no problem but photographically this needs to be corrected by an optical corrector called a field flattener.
All different flavors of refractor telescopes can be found in this section!
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