11/10/2023 0 Comments Refractor telescope lensesAn apo can be made with as few as two or three elements if one of them is an extra low or super low dispersion glass.Įrnst Abbe established what an apochromatic lens must do. Telescopes that are truly color free are called Apochromatic telescopes or apos. Remember, in a telescope color dispersion is bad so low dispersion glass is good! Since the colors are closer together, fewer elements are needed to make a color-free telescope. This glass disperses color less than standard glasses as depicted in this diagram. It required ten elements but it was truly color free.Īs time went by glass technology improved, allowing for the invention of new (and expensive) types of glass, including low-dispersion glass. It was a microscope lens that used the standard optical glasses available at that time. It was Ernst Abbe the head of the Zeiss company who developed a truly color-free lens in 1868. While two conventional glasses can reduce color it does not get rid of it entirely as shown at the right. This new type of objective lens was called an "achromat" meaning no color. His objective eliminated some but not all of the false color. He combined a crown glass lens with a flint glass lens, making a two element objective lens. In the early 1700s, Chester Moore Hall believed it was possible to combine different glasses to reduce false color. However, what Newton did not realize is that when combining glasses that disperse colors differently, false color can be cancelled out. Newton said refractors will always have false color. In 1668 Isaac Newton invented the reflecting telescope, which used mirrors instead of lenses. A simple lens like this acts like a prism, dispersing the colors that make up white light, and shows much false color. In 1609 Galileo first used a telescope with a simple, one-element objective to view the heavens. Telescope objectives that are poorly figured due to hurried production give poor performances even if they use the best glass. The reason I am writing this is to clear up some common misconceptions regarding glass type and what makes a premier telescope. Moreover, glass type alone cannot determine the quality of a telescope. While the answer is currently yes, there are three other glass types that provide the same level of performance based on our experience and testing. Some people ask if Stellarvue apo triplets are made with FPL53.
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