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The refractor telescope has a straightforward design of an objective lens on one end of a tube and an eyepiece at the other. These are some of the pluses of owning a refracting telescope:
1. You'll get a low maintenance, straightforward telescope with a refractor.
2. The refractor telescope gives you high contract, sharp images.
3. The tight air seal of a refractor telescope keeps air currents from affecting your view.
4. Whether you're interested in long distance terrestrial viewing or looking at the planets and stars, the refractor telescope is ideal.
A refractor telescope, also known as a dioptric, was the first type of telescope invented. The telescope is a long tube with an objective lens at the front, which draws in the light and sends it to the eyepiece on the opposite side. The eyepiece magnifies the image of the viewed object, allowing a stargazer a better view of the night sky. The refractor telescope is the preferred piece of equipment by astronomers to view the planets and double stars due to its ability to give the viewer a clear contrast between light and dark areas.
Larger sized refractors include telescopes with apertures above 80mm to 200mm and even higher. In this class, you can start comparing the pros and cons of a refractor telescope versus a reflector or catadioptric with a similar aperture size. You can purchase one of the other types of telescopes with a comparable performance and a smaller cost. For the larger sized refractors with a 200mm aperture, you can pay upwards of $10,000 for some models. Astronomy enthusiasts with a die-hard allegiance to the refractor telescope cite the low maintenance, ease of use, and bright, clear contrasting images as a reason to stick this type of telescope, even with the high price tags.
Moving up in aperture range to the mid sized refractor telescopes puts you on another category of stargazing. With 76mm and 80mm refractor telescopes, the price of the equipment jumps up substantially. This is because you are no longer dealing with a beginner's market and the demand for these mid sized refractor telescopes is not as great. With quality mid sized refractor telescopes, you can expect to see details on planets you cannot see with a 60mm refractor telescope. One good measure of comparison would be a view of the Cassini Division, a dark band between the two brightest rings around Saturn. With a 60mm refractor, the Cassini Division would not be visible. However, with a 76mm refractor telescope, the band would become apparent. A 76mm refractor would also increase the light gathering power by 60 percent from a 60mm refractor. Deep sky objects not visible with a 60mm refractor would come into view with a 76mm refractor.
Though simple in design, the refractor telescope has its own set of drawbacks. For the refractor telescope, caution should be exercised when selecting a less expensive model. According to “Stargazing With A Telescope” by Robin Scagell, you should start with a good quality 60mm lens when considering a refractor telescope. The disadvantages of a refractor telescope include:
1. This type of telescope costs more than its Newtonian and catadioptric counterpart when you compare models of the same aperture size.
2. The refractor telescope can be ill suited for viewing faint astronomical bodies due to the design of the telescope and aperture.
3. Though the images come across clearly, you may get unwanted color fringes around the objects in view.
4. The lower end models of the refractor telescope tend to lack enough quality for decent astronomy viewing.
Aperture is one consideration when selecting your refractor telescope, but the details are in the focal length. For instance, if you are selecting a 60mm refractor telescope, you might find one has a focal length of 900mm and another with a focal length of 1000mm. If you want to see the details of a planet in the night sky, you should choose a refractor telescope with the longer focal length. A longer focal length will give you a larger, but dimmer image while a shorter focal length will give you a brighter, smaller image.
A refractor telescope has many variables which make up the final view you'll see in the night sky. Aperture size is one key component to determining your view of the stars and planets. If you're in the market for a refractor telescope, you might have considered whether or not it is worth it for you to purchase a 70mm refractor telescope versus a 60mm one. With a 60mm refractor telescope, you will be able to see deep sky objects in good weather conditions. But keep in mind what you see will look small and blurry to your eye. With a 70mm refractor telescope, you will gain one-third more light, making your view of deep sky objects much clearer through your telescope.
If you are looking for a beginning or entry-level telescope, you might have considered one of the smaller refractors out on the market and wondered whether they have sufficient power to provide you with a decent view of the night sky. If you are contemplating 50mm or 60mm refractors, you will find an inexpensive, starter model for stargazing. With these smaller refractors, bright planets will come into view. You can also navigate your way through double stars, nebulae and galaxies. The important thing to keep in mind is to look for quality over aperture size. A well-built 50mm refractor telescope will be a better purchase than a 60mm refractor telescope.
When you have three models of refractor telescopes to choose from, you can make a decision tailor-made to suit your needs. Sky & Telescope magazine reviewed three ultraportable telescopes in their May 2006 issue, all made by ZenithStar. If having mobility in a well-designed refractor telescope with a high level of craftsmanship sounds appealing to you, check out these models:
ZenithStar 66 Petzval – This model retails for $350 and is the most affordable of the line. It represents good value for your dollars and includes a 63 mm aperture, 388 mm focal length, and a 1.25” and 2” eyepiece. This portable telescope weighs only 3.5 pounds. The downside to this particular model is the requirement of the additional purchase of an extension tube or star diagonal to reach focus.
ZenithStar 66 APO – This portable telescope has a 66 mm aperture, 397 mm focal length, and a 1.25” and 2” eyepiece as well. At $400 retail, it is still a good purchase for the money and has top-notch optical quality. Like the Petval, this model also needs additional accessories to reach focus.
ZenithStar 66 SD - This high-end model among the three refractor telescopes rates well with its excellent mechanical craftsmanship and near perfect apochromatic optical performance. It comes with a 66 mm aperture, 461 mm focal length, and a 1.25” and 2” eyepiece. The downside to this model, like the other two, is the requirement of an accessory purchase to reach focus. The ZenithStar 66 SD retails for $500.
|Jennifer Mathes, Ph.D.|