Astronomical equipment #2 : Refracting telescope

in #steemstem6 years ago (edited)

Galileo's telescope began the history of the telescope in 1609. In contrast to the Newton telescope, it gives a simple image (not inverted as in a mirror instrument), which is why it is great for terrestrial observations, and due to its rather small diameter, it also works well in observations of planets and the moon.


Apochromatic refractor - construction

By Tamasflex link [CC BY-SA 3.0 license]


In lunettes, the light focuses the lenses. Unfortunately, this type of telescope has an optical defect called chromatic aberration (absent from Newton's reflecting telescope). The disadvantage is the creation of colorful borders around bright objects. Depending on the type of correction of this optical defect, we distinguish types of refractors such as:


Achromat - the cheapest and popular lens telescope, its lens is made of 2 elements. A refractor of this type corrects chromatic aberration for the two most important parts of the spectrum of light (red and blue).

Semi apochromat - a term used by refractor manufacturers for those models whose aberration correction is slightly lower than in Apochromats, and better than in achromats. These are usually 2 and 3 lenticular constructions called ED. These are simply mid-range spotting scopes.

Apochromat - Lens with 2 to 4 lenses with good correction. Usually made of special types of glass. Such a telescope corrects chromatic aberration for three colors (red, blue and green). Such a construction, even on bright objects, doesn't show additional colors. It is expensive equipment for professionals, especially recommended for astrophotography.

Superachromat - The lens of this refractor corrects chromatic aberration for many colors, thus ensuring clear images without any distortions. Such constructions are rare and very expensive.


Diagram of construction of an ordinary achromat refractor

By Tamasflex link [CC BY-SA 3.0 license]


Below we see one of the Apochromats with good color correction. Qualitatively the image in such an instrument is better than in Newton's telescope, especially on bright objects like planets. Here a good refractor will show a picture much more contrasting than in a mirror telescope, where the secondary mirror overrides the center of the main mirror (this construction reduces the contrast of images). Unfortunately, such a telescope with a diameter of just 102 mm (4 inches) costs about $ 3000. For comparison, a two-times larger Newtonian telescope with a diameter of 200 mm (8 inches) costs $ 250.


Takahashi TSA-102S high-tech apochromatic refractor

By Marie-Lan Nguyen (Jastrow) link [CC BY 3.0 license]


Astronomy enthusiast in most cases will choose Newton's telescope, because it is the most profitable. Although mirror instruments aren't the kings of planetary observation, their size and light-gathering ability needed to observe nebular objects is significant. The Newton's 8-inch telescope will give you a lighter and twice as sharper image than the 4-inch Apochromat. On the Newton planets, a bright image will be shown without contrast, and the refractor will reveal the true color of the planets. However, it seems to me that the profitability of such a purchase is small, they are bought more for astrophotography. In contrast, I generally advise against the purchase of cheap Achromat type scopes. In this comparison, Newton wins in all respects (well, apart from terrestrial observations - inverted image). Thank you for reading.


Greetings to lovers of Astronomy!


References:

Apochromat
Refracting telescope
Achromatic telescope
List of telescope types
and my knowledge...

All rights reserved by @astromaniac 2018

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Niestety tak to już jest z tymi szkłami jak w fotografii. Chcesz mieć coś dobrego i niezawodnego trzeba słono zapłacić. Podam Ci taką małą różnice dwóch obiektywów marki c---n Pierwszy obiektyw stało ogniskowy 50mm światło 1,8 koszt 400zł drugi światło 1,2 i cena 5600zł. Tam gdzie trzeba wybierać w optyce nie ma kompromisów.
Kolejny twój artykuł który mnie wciągnął. Super.

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