Focusing the Telescope, Attaching a Finder Scope

Collimation adjustment push‑pull screws

Knurled

silver

grip‑ring Focus lock

knob

Coarse focus

knobs

	Focus
		10:1 Fine
	tension knob
		focus knob

Figure 5: Details of the linear bearing Crayford focuser.

extension (1 x 1" and 1 x 2"). Larger 2" eyepieces may only require two inches of extension.

Focusing the Telescope

One of the exciting new features of the Orion Ritchey- Chrétien optical tubes is the inclusion of the new linear bear- ing Crayford focuser. Instead of the traditional Crayford-style focuser — which uses a roller tensioned against the drawtube

—the new linear bearing focuser has a track on the draw- tube with beveled edges and rollers within “grooves” along the edges. This allows you to more effectively lock down the fo- cuser with heavy payloads such as a large eyepiece, a DSLR, or a large CCD Imager. Image shift is reduced by stabilizing the drawtube within the focuser housing.

For astronomical viewing, out-of-focus star images are very diffuse, making them difficult to see. If you turn the focus knob too quickly, you can go right through focus without seeing the image. To avoid this problem, your first astronomical target should be a bright object (like the Moon or a planet) so that the image is visible even when out of focus. There is also a 10:1 fine focus adjustment. Every 10 turns of the small knob equals a single turn of the large knob to enable the micro- adjustment necessary for the sharpest images possible. Use the coarse focus knob to adjust the telescope until your object is as close to focus as possible, then make fine adjustments with the black outside knob

Attaching a Finder Scope

A finder scope is a small, wide-field instrument used to help locate and center objects in the main field of your telescope. A finder scope usually has a built-in crosshair reticle that shows the optical center of the finder’s field of view. On some models the center is indicated with an LED display.

A finder scope dovetail base has been pre-installed on your Ritchey-Chrétien optical tube assembly making it easy to use any Orion finder and many others using a similar bracket. Installing a finder scope is very simple:

Finder scope dovetail holder

Metal thumbscrew

Figure 6: Finder scope dovetail base.

1.Loosen the metal thumbscrew on the side of the dovetail base.

2.Insert the bracket into the dovetail from the back of the telescope, until it stops.

3.When the finder bracket is securely in place retighten the metal thumbscrew.

Inserting a Star Diagonal

A star diagonal is a prism that diverts the light at a right angle to the light path of the telescope. This allows you to observe in positions that are physically more comfortable than if you looked straight through the scope. Your telescope is equipped with a 2" focuser and includes a 1.25" adapter, allowing maximum versatility when choosing accessories. To insert an optional diagonal simply loosen the knurled thumbscrew on the side of the focuser drawtube and insert the chrome barrel of the diagonal, then re-tighten the thumbscrew. The built-in brass compression ring will provide uniform tension on the diagonal and prevent marring of the chrome surface.

Inserting an Eyepiece

An eyepiece magnifies the image focused by the telescope. The eyepiece fits into either the focuser directly or a star diag- onal. Eyepieces are commonly referred to by focal length and barrel diameter. The focal length of each eyepiece is printed on the eyepiece body. The longer the focal length (i.e., the larger the number) the lower the eyepiece magnification, the shorter the focal length (i.e., the smaller the number) the high- er the magnification. Generally, you will use low to moderate powers when viewing. Use the following formula to calculate magnification:

Magnification = Focal Length of Telescope (mm) Focal Length of Eyepiece (mm)

To install an optional eyepiece:

1.Loosen the setscrew on the star diagonal until the tip no longer extends into the inner diameter of the eyepiece end of the diagonal.