Orion 9874 Setting Up and Using the Equatorial Mount, 1200mm = 48x 25mm, 1200mm = 120x 10mm

Dec. lock lever

Dec. setting circle

Front opening

Azimuth adjustment knobs (2)

			(R	Right
			Ascension
			.	.
				)
		) axis		axis
	(Dec	.
Declination

Figure 7. The Atlas EQ Mount.

R.A.

setting‑circle

R.A. lock lever

Polar axis finder‑scope

Latitude scale

Latitude adjustment L‑bolts

The Atlas 10 EQ has a focal length of 1200mm, which when used with the supplied 25mm eyepiece yields a magnification of:

1200mm = 48x 25mm

The magnification provided by the 10mm eyepiece is:

1200mm = 120x 10mm

The maximum attainable magnification for a telescope is directly related to how much light it can gather. The larger the aperture, the more magnification is possible. In general a fig‑ ure of 60x per inch of aperture is the maximum attainable for most telescopes. Your Atlas 10 EQ has an aperture of 10 inches, so the maximum magnification would be about 600x. This level of magnification assumes you have ideal conditions for viewing.

Keep in mind that as you increase magnification, the bright‑ ness of the object viewed will decrease; this is an inherent principle of the laws of physics and cannot be avoided. If magnification is doubled, an image appears four times dim‑ mer. If magnification is tripled, image brightness is reduced by a factor of nine!

Always start with your lowest power eyepiece and work your way up. Start by centering the object being viewed in the 25mm eyepiece. Then you may want to increase the magnification to get a closer view. If the object is off-center (i.e., it is near the edge of the field of view) you will lose it when you increase magnification since the field of view will be narrower with the higher-powered eyepiece. To change eyepieces, first loosen the securing thumbscrew on the focuser’s 1.25" adapter. Then carefully lift the eyepiece out of the holder. Do not tug or pull the eyepiece to the sides, as this will knock the telescope off its tar‑ get. Replace the eyepiece with the new one by sliding it gently

into the holder. Re-tighten the thumbscrew, and refocus for your new magnification.

Using 2" eyepieces

The Atlas 10 EQ’s focuser is capable of accepting optional 2" eyepieces. To use 2" eyepieces you must remove the 1.25" adapter from the focuser by loosening the two thumbscrews that hold it in place (Figure 4). Once this adapter is removed, insert a 2" eyepiece into the focuser and use the same thumb­ screws to secure the larger eyepiece. 2" eyepieces typically provide a wider field of view than 1.25" eyepieces.

6.Setting Up and Using the Equatorial Mount

When you look at the night sky, you no doubt have noticed that the stars appear to move slowly from east to west over time. That apparent motion is caused by the Earth’s rotation (from west to east). An equatorial mount (Figure 7) is designed to compensate for that motion, allowing you to easily “track” the movement of astronomical objects, thereby keeping them from drifting out of your telescope’s field of view while you’re observing.

This is accomplished by slowly rotating the telescope on its right ascension (R.A.) axis, using the built in motor drive. But first the R.A. axis of the mount must be aligned with the Earth’s rotational (polar) axis—a process called polar alignment.

Polar Alignment

For Northern Hemisphere observers, approximate polar align‑ ment is achieved by pointing the mount’s right ascension axis at the North Star, or Polaris. It lies within 1° of the north celes‑ tial pole (NCP), which is an extension of the Earth’s rotational

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