Celestron C8-NGT, C10-N manual Focusing, Aligning the Finderscope, Calculating Magnification

Actual image orientation as seen

with the unaided eye

Upside-down image, as viewed though a Newtonian telescope

Figure 4-2

Focusing

To focus your telescope, simply turn the focus knob located directly below the eyepiece holder. Turning the knob clockwise allows you to focus on an object that is farther than the one you are currently observing. Turning the knob counterclockwise from you allows you to focus on an object closer than the one you are currently observing.

•If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an eyepiece attached to the telescope. However, when using a camera you should always wear corrective lenses to ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.

Aligning the Finderscope

Accurate alignment of the finder makes it easy to find objects with the telescope, especially celestial objects. To make aligning the finder as easy as possible, this procedure should be done in the daytime when it is easy to find and identify objects. The finderscope has a spring-loaded adjustment screw that puts pressure on the finderscope while the remaining screws are used to adjust the finder horizontally and vertically. To align the finder:

1Choose a target that is in excess of one mile away. This eliminates any possible parallax effect between the telescope and finder.

2Release the R.A. and DEC clamps and point the telescope at your target.

3Center your target in the main optics of the telescope. You may have to move the telescope slightly to center it.

4Adjust the screw on the finder bracket that is on the right (when looking through the finder) until the crosshairs are centered horizontally on the target seen through the telescope.

5Adjust the screw on the top of the finder bracket until the crosshairs are centered vertically on the target seen through the telescope.

Image orientation through the finder is inverted (i.e., upside down and backwards left-to-right). This is normal for any finder that is used straight-through. Because of this, it may take a few minutes to familiarize yourself with the directional change each screw makes on the finder.

Calculating Magnification

You can change the power of your telescope just by changing the eyepiece (ocular). To determine the magnification of your telescope, simply divide the focal length of the telescope by the focal length of the eyepiece used. In equation format, the formula looks like this:

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