Meade DS-2000 instruction manual Choosing an Eyepiece, The Barlow Lens, Definition

Fig. 15: 25mm and 9mm eyepieces.

DEFINITION:

A capital "X" is used to denote an eye- piece's (or a Barlow's) power or magnification. For example, "40X" is read as "40-power."

image) has been aligned to the main telescope. Fig. 13B shows these same images after the viewfinder and main telescope are aligned.

5.Check this alignment on a celestial object, such as the Moon or a bright star, and make any necessary refinements.

Choosing an Eyepiece

A telescope’s eyepiece magnifies the image formed by the telescope’s main optics. Each eye- piece has a focal length, expressed in millimeters, or “mm.” The smaller the focal length, the higher the magnification. For example, an eyepiece with a focal length of 9mm has a higher magnification than an eyepiece with a focal length of 25mm.

Your telescope comes supplied with a low-powered 25mm eyepiece which gives a wide, com- fortable field of view with high image resolution.

Low power eyepieces offer a wide field of view, bright, high-contrast images, and eye relief dur- ing long observing sessions. To find an object with a telescope, always start with a lower power eyepiece such as a 25mm. When the object is located and centered in the eyepiece, you may wish to switch to a higher power eyepiece to enlarge the image as much as practical for pre- vailing seeing conditions.

NOTE: Viewing conditions vary widely from night-to-night and site-to-site. Turbulence in the air, even on an apparently clear night, can distort images. If an image appears fuzzy and ill-defined, back off to a lower power eyepiece for a more well-resolved image.

The power, or magnification of a telescope is determined by the focal length of the telescope and the focal length of the eyepiece being used. To calculate eyepiece power, divide the tele- scope's focal length by the eyepiece's focal length. For example, you may wish to use a 25mm eyepiece with the DS-2000 model DS-2114S. Look up the focal length of the DS-2114S under "Specifications: DS-2114S," page 33. The focal length is listed as 1000mm.

Telescope focal length divided by Eyepiece focal length = Eyepiece power

1000 25 = 40

The eyepiece power, or magnification is therefore 40X (approximately).

The Barlow Lens

Some Meade telescopes include a power multiplier called a Barlow lens. Consisting of a lens mounted in a 4"-long (10cm) tube, the Barlow doubles or triples the power obtained when an eyepiece is used alone. In the example above, a 25mm eyepiece results in 40X magnification with the DS-2114S telescope; when this same eyepiece is used in conjunction with a 2x Barlow lens, power is doubled to 80X. To use the Barlow, insert it into the diagonal prism (refractor models only) or eyepiece holder, followed by the eyepiece.

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