Astronomer G. P. Bond of Harvard College Observatory photographed a comet called Donati using a telescope in September 1858. The comet was discovered by Giovanni Battista Donati, professor of astronomy, in June 1858, and was the first astronomical object to be photographed by a telescope.
The mid to late twentieth century saw an evolution of astronomical color photography using telescopes. In the past few decades, telescopes have become fairly affordable and offer a great way to start astrophotography at home.
The simplest way to photograph celestial bodies with a telescope is by attaching a camera to the telescope. This can be done by removing the lens of the camera and the eye-piece of the telescope to put the camera on the place from where the eye-piece was removed. The objective lens of the telescope will act as the primary lens of the camera. Telescopes come with an array of specifications, which could make it difficult to choose, especially if you are a beginner.
Choosing the right telescope
There are three categories for telescopes to choose from: refractor, reflector, and compound. Refractors are the first kind of telescopes invented in the early seventeenth century. Its primary light-gathering component is a lens that is permanently aligned and mounted with a mirror in an optical tube, also known as optical tube assembly (OTA). For a reflector telescope, its primary light-gathering component is a mirror. As for a compound telescope, it uses a combination of mirrors and lenses to gather light.
The important factors to keep in mind before buying a telescope are its image quality, maintenance, aperture size, and affordability. To produce a high-quality image in astrophotography, the telescope should be able to reduce chromatic aberration, which is the inability of a lens to focus light of different colors on the focal plane. This also results in the production of haloes around bright objects.
The chromatic aberration is highly reduced in the reflector telescopes such as Newtonian, Cassegrain, and Ritchey-Chretien telescopes. The Doublet or Triplet refractor telescopes use two or three lenses made of glass to reduce chromatic aberration. Compound telescopes or hybrid telescopes such as Schmidt-Cassegrain, Maksutov-Cassegrain are also immune to chromatic aberration.
Doing maintenance on the telescope
Refractor telescopes are the easiest to maintain because the optical components do not require collimation, which is a process of aligning all the elements of an optical tube. Meanwhile, the reflector telescopes will require regular optical alignment.
The compound telescopes use both reflective and refractive processes on the collected light, which gives them a long focal length. The focal length of a telescope is the distance between the center of the lens or the mirror and the point at which the light is focused. The entire assembly is fitted in a compact tube and is lightweight, making it easy to maintain. However, it will still require timely collimation.
Considering aperture size
The aperture size, which is the diameter of the primary lens or mirror that gathers light, of a telescope, is one of the most important features to be considered before making a purchase. A telescope with an aperture size between 4 and 6 inches will be a good starting point for beginners.
For a more detailed view of astronomical objects outside the solar system such as galaxies, nebulae, star clusters, and so on, a telescope with an aperture size more than 8 inches will be required. This kind of telescope though can get very expensive.
Telescopes are available in a wide range of prices, and there are plenty to choose from. A refractor can offer great deep-sky views and images, but it gets very expensive as the aperture size increases. Reflectors and compound telescopes may not be as easy to maintain as the refractors but are more affordable and provide stunning views as well. Following is the list of some high-quality and affordable telescopes that you can purchase in 2020.
1. Orion StarBlast 102mm
The Orion StarBlast 102mm is a doublet refractor telescope with an aperture size of 4 inches (102mm) and a focal length of 600mm. Its travel refractor kit comes with an alt-azimuth mount, which is a stainless steel tripod that can be moved in altitude, up and down, and azimuth, side to side, positions, and two eye-pieces.
It also has a finder scope, a low power telescope attached to the optical tube to assist in locating the objects. Being a doublet refractor it will be easy to maintain, and it will not have chromatic aberration. The Orion StarBlast 102mm is priced at $329.99.
2. Celestron NexStar 130SLT
The Celestron NexStar 130SLT is a Newtonian reflector telescope that has an aperture size of 5.1 inches (130mm) and a focal length of 650mm. It offers detailed views of the solar system and comes with an alt-azimuth mount, two eye-pieces, and a finder-scope.
The mount is automated and controlled by a remote attached to it. This telescope is great for deep-sky viewing and costs $499.95.
3. Celestron NexStar 5SE
The Celestron NexStar 5SE is a Schmid-Cassegrain telescope which is known to be good for astrophotography. Schmid-Cassegrain offers a long focal length in a compact optical tube. They also do not have chromatic aberration.
The aperture size is 4.9 inches (125mm) and a focal length of 1250mm, making it able to view bright deep-sky objects. It comes with a computerized alt-azimuth mount, one eye-piece, and a finderscope. The Celestron NexStar 5SE is priced at $699.00.
4. Meade StarNavigator NG 125mm
The Meade StarNavigator NG 125mm is a Maksutov-Cassegrain telescope. Maksutov-Cassegrains, like Schmid-Cassegrains, have long focal lengths and are fitted in a short optical tube. The focal length of this telescope is 1900mm, which is more than enough to view deep sky objects.
It comes with a computerized GoTo mount, a telescopic mount that automatically points the telescope to the object selected by the user. The entire assembly of the Meade StarNavigator NG 125mm costs $499.00.
5. Orion SpaceProbe 130ST
The Orion SpaceProbe 130ST is a reflector telescope that has an aperture size of 5.1 inches (129.54mm) and a 650mm focal length. It comes with two eye-pieces, a finder scope, and an equatorial mount.
The equatorial mount moves across the sky in a curved axis, which is aligned with the axis of the earth. This movement mount helps in tracking objects in the sky easily. The Orion SpaceProbe 130ST costs $309.99.
6. Orion StarBlast 6i Intelliscope
The Orion StarBlast 6i Intelliscope is a reflector telescope with an aperture size of 5.9 inches (150mm) and a focal length of 750mm. It comes with two eye-pieces, a finder-scope, and an alt-azimuth mount. The entire assembly will weigh 23.5lbs and can be easily carried to less polluted areas for stargazing. The price of this telescope is $499.99.
As you can see, there’s a variety of telescopes to start from. However, it’s important to think about what you want to capture with the telescope, how you’ll maintain it, and if it’s within your budget. In any case, this initial list of telescopes can be a starting investment into astrophotography.
Photo credits: The feature photo has been taken by Taneli Lahtinen. The first photo in the body of the article has been taken by Patrick Hendry. The second photo has been taken by Zhijian Lyu.
Sources: arXiv / RTSRE Journals / Making Beautiful Deep-Sky Images: Astrophotography with Affordable Equipment and Software by Greg Parker / Astrophotography for the Amateur by Michael A. Covington
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