Additionally, reflector telescopes are not susceptible to color fringing in the same way that doublet refractors are. If you're looking for more bang for your buck in terms of aperture, reflectors are a great way to go. This is especially true for Dobsonians , which come with their own easy-to-use rocker-box mount. Reflector telescopes can be a great value with many conveniences. They can also come in a variety of sizes and can get quite large. With this in mind, purchasing the largest reflector you can afford is a great low-cost way to get a high-aperture scope.
Just make sure you can store and transport it safely. There are some things you should consider about the reflector design. By default, the image you see through a reflector's eyepiece will be upside down. For this reason, you'll want to use your scope's finder to line it up with the objects you want to see before looking through the eyepiece.
Most modern reflecting telescopes come with a finderscope or a red dot finder , so you most likely won't have to make an additional purchase to acquire this. Additionally, reflector telescopes will sometimes require a process called collimation, which consists of adjusting the reflector's mirrors to ensure they stay in proper alignment with each other. When properly maintained, a large reflector is a great way to view smaller or far away objects with great clarity, and it is of excellent value for achieving high-aperture viewing.
If you are interested in astrophotography, purchasing a refractor is a better option because of it's specialized optic design that captures deep space objects like galaxies and nebulae. If you are interested in brighter celestial objects like the Moon or planets or a beginner, a reflector telescope is ideal.
Due to reflectors larger apertures at similar prices, they're usually going to be the best choice for almost all things visual. If the surface is smooth, like a mirror, the light will reflect in a predictable way. Curved mirrors can bend light and make parallel light rays converge to a focus. This focus is directly in the path of the incoming light, so there are several ways of making images from the mirror visible.
One is called a Newtonian reflector, where a flat mirror is used to point the light rays out to an eyepiece. There are several other types of reflectors that solve the issue of where to focus the light in different ways. Cassegrain reflectors have a convex secondary mirror and a hole in the middle of the primary mirror.
Disclaimer: Optical performance is a very complicated topic. Inexpensive refractor telescopes often use a simple refracting lens, made of a single piece of glass. The challenge with this is that it introduces a blurring of certain color wavelengths in the image, called chromatic aberration.
Different wavelengths of light require slightly different focal lengths after refraction. For smaller refractors, this is not really a big deal. However, it starts to become more important as you go beyond lower-powered refractors. Chromatic aberration can be mitigated or reduced using a high-quality achromatic objective lens sometimes in combination with a fringe filter or — even better — with an apochromatic lens a.
These higher-quality refractors provide ultra-sharp image quality — making them a great choice for detailed viewing of solar system objects. High-quality refracting telescopes also make for stunning astrophotography. However, reflectors can still suffer from a phenomenon known as spherical aberration , where distortion is caused by differences in the focus of light across the surface of the mirrors.
Note: Refractors can suffer from this too, but the higher quality lenses do a good job correcting for it. The cheapest kind of mirror to manufacture is spherical in shape. However, spherical mirrors result in higher spherical aberration. High-quality reflectors employ one or more parabolic mirrors. And note: There are many differences between the miscellaneous sub-types of reflectors. Not enough time to go into it here. For refractors, consider getting an achromatic or apochromatic lens.
For reflectors, look for true parabolic mirrors and high-quality engineering. For visual astronomy, we generally recommend you get the largest aperture you can afford. As long as the telescope is a good fit for your needs in other ways — especially in terms of size, weight, portability, and ease of use.
Remember: The amount of light a telescope can collect is related to the square of the aperture size. For refractors, as the diameter of the aperture increases, the cost and bulk of the lens increases exponentially faster. For this reason, most amateur astronomers prefer reflector telescopes for deep-sky visual astronomy. In fact, when it comes to large aperture sizes, reflectors are pretty much the only game in town for the average amateur. Make sure you know the telescope size that you can best handle.
Bottom line: For deep-sky visual astronomy, there is no substitute for a large-aperture reflector telescope. Most amateur astrophotographers prefer the simplicity of a high-quality apochromatic APO refractor telescope.
There are also some great reflector options for astrophotography, but refractors have some key advantages. For visual astronomy, you do need a large aperture, because you need to get as much light as possible into the telescope all at once so you can see the target with your eyes. However, with astrophotography, what you really care about is the amount of light per pixel — so the speed of the telescope becomes more important.
And remember, you get the focal ratio by dividing the focal distance by the aperture size. So, for astrophotography, a fast 80mm APO refractor can outperform a larger but slower telescope. The newton telescopes are the most widespread reflectors in the market because of their easy building process and their low cost. The light coming from a star goes inside the optical tube and is first reflected on the primary mirror, located at the extremity.
This primary mirror is the master piece of the reflector. It has to collect and make the light beams converging towards the eyepiece holder, the element where we put our eyes. Here, it is necessary to find a way to make the light beams going out of the tube. Therefore, a secondary mirror is installed next to the front aperture of the telescope, enabling beams to be deviated on the side of the telescope, and so, to observe an image.
The bigger the mirror is, the brighter the objects appear in the eyepiece. However, a big mirror could quickly emphasize the optical aberrations of the telescope.
Theoretically, getting a perfect round dot of a star requires having a newtonian reflector made with a hyperbolic primary mirror. In fact, such a mirror is relatively expensive and telescopes manufacturers choose rather a parabolic mirror instead, far simpler to build. However, a parabolic mirror is facing a defect: the coma aberration which deforms and elongates the star around the fields of view.
More often, the low-cost manufacturers do not use nor a hyperbolic neither a parabolic mirror but a spherical mirror. With such a geometry, you will never manage to focus perfectly the image of a star with your reflector, because of spherical aberration ; a delicate situation considering that astronomy requires to observe and photograph faint and diffuse celestial objects.
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