TECHNICAL INFORMATION
We hope the following information helps you make a decision on which Telescope is right for you. If you need additional information or perhaps a suggestion of which model would suit you best then please give us a call 01903 200456 open every day.
TYPES OF TELESCOPE
REFRACTORS - An optical system that utilizes a series of glass lenses to refract or bend the light from a distant object such that it can be focused to a point and magnified by an eyepiece. Popularized by Galileo in the 17th century, it is sometimes referred to as a Galilean refractor. Refractors are less affected by atmospheric instabilities, making them perfect for observing the moon and planets. Perfect for first time and novice astronomers, small refractors are lightweight, portable and require very little maintenance. And, if you're interested in viewing both land and celestial objects, refractors are equipped for both uses.
REFLECTORS - The optical system in a reflector uses a primary mirror to reflect the light from a distant object such that it can be focused to a point and magnified by an eyepiece. Popularized by Sir Isaac Newton in the 17th century, it is sometimes referred to as a Newtonian reflector. Reflectors feature larger apertures for a wide range of viewing at an affordable price. Designed with the eyepiece located at the top of the tube, reflectors are more comfortable to use for viewing night-sky objects such as nebulae, the moon, planets and galaxies. Reflectors tend to be heavier and larger than refractors.
MAKSUTOV-CASSEGRAIN - A design that utilizes a spherically curved front lens element in conjunction with a similarly curved primary mirror. This configuration provides incredibly sharp images in a compact folded-light path package. The total optical system provides a focal length much longer than the actual optical tube body length.
GETTING THE BALANCE RIGHT
The mark of a good telescope is not how much magnification it has, this is just one part of the equation. Since most objects in the sky are rather large, high magnification isn't necessary. Rather, a telescope that gathers lots of light is needed to make dim objects appear brighter and sharper. The power or magnification contributes to the overall size and bulk of the telescope. This is because as the power increases, so must the physical size of the objective lens to maintain a clear image.
OPTIMUM MAGNIFICATION (POWER) - The optimum magnification demonstrates how far you can go with your telescope without adding an enhancing lens such as a Barlow Lens. The magnification of a telescope is determined by dividing its focal length by the size of the eyepiece being used. For example, a 500mm telescope with a 5mm eyepiece would magnify objects 100x. Thus, a telescope can provide nearly any magnification required depending on the size of the eyepiece used. Since most objects in the sky are rather large, high magnification isn't necessary. Rather, a telescope that gathers lots of light is needed to make dim objects appear brighter and sharper. The power or magnification contributes to the overall size and bulk of the telescope. This is because as the power increases, so must the physical size of the objective lens to maintain a clear image.
OBJECTIVE LENS SIZE (OR APERTURE) - The aperture relates directly to how bright images will appear and how much detail is revealed. The larger the objective lens, the better. The size of the telescope's objective lens, or aperture, limits the amount of power that can be used effectively. As the magnification of an object increases, the brightness of the image decreases. This is because the light gathered by the telescope is being spread over a larger area. Aperture also limits the clarity of an image at increased magnification. When magnified beyond an aperture's recommended power, the image dims and becomes fuzzy.
EYEPIECES - Lower power eyepieces (i.e. bigger) provide a wider field-of-view and a brighter image making them ideal for viewing the full moon and planets, star clusters, nebulae and the constellations. To focus in on the finer details of the moon and planets such as mountains, ridges and craters, use an eyepiece with higher magnification (i.e. smaller).
BARLOW LENS - An auxiliary lens that increases the power by a factor. For example, a 3x Barlow triples the magnification of the telescope.
MOUNTS
There are three basic types of telescope mounts, the altitude-azimuth (or altaz), the equatorial and an automated Star Locating mount.
Altaz mounts are the easiest to operate and are generally ideal for land based viewing i.e. panoramic views and first-time astronomers. However tracking celestial objects is more difficult.
Equatorial mounts are preferred by more experienced astronomers. Equatorial mounts make finding and tracking celestial bodies across the sky easier once you have mastered the technique, which for most stargazers is part of the hobby and adds to their enjoyment. Some equatorial mounts have motor drives which keep your object in view throughout the night.
Star Locating mounts take the guess work out of star gazing. There are several on the market but essentially most work like this. Align the telescope to north, tell it where it is in the world and the time and date. The telescope can now navigate itself to thousands of stars, planets, galaxies and nebulae taking you on a tour of the night sky.
ERECTING LENS / STAR DIAGONAL
Lens used with a refractor telescope when viewing land-based objects to correct the normally upside-down image provided by an astronomical telescope.
FINDERSCOPE
On most astronomical telescopes a lower powered finderscope with a wider field-of-view lets the user quickly locate the object to be viewed by the high-magnification main telescope. There are two types of finderscopes, optical and red dot.
FOCAL LENGTH
The measured light path of the optical system (tube length), typically measured in millimetres. The larger the number the more magnification can be achieved.
FOCAL RATIO
Equation of Focal Length and Aperture the lower the number the brighter the image.
STELLAR MAGNITUDE
All night sky objects have been given a stellar magnitude, telescopes have a limit (based on size) above which they cannot see objects because they are too faint i.e. if your telescope has a Stellar Magnitude Limit of 10 you will not be able to see objects with a Stellar Magnitude of 10.1 or more. To give you a comparison a normal set of eyes have a Stellar Magnitude Limit of 2.5 so we cannot see objects above this without a telescope.
LIGHT GATHER
A measurement based on size which indicates how much light enters the telescope and ultimately the brightness and detail of the object.
SO REMEMBER
When selecting a telescope, consider which target objects you plan to explore as well as your level of experience. For viewing most night sky objects, you'll want a telescope with as much aperture as possible. If you intend to view land, wildlife or panoramic scenery then your best bet is a Refractor because it can display the image the right way up. Keep in mind that as the size of the objective lens or mirror increases, so does the size of the telescope. So be sure to select a telescope that isn't too heavy to manage or too complicated for you to set up especially if portability is a necessity.
Still confused or just need some help please call us on 01903 200456 we are happy to help.
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