Aligning the Finder Scope, Focusing the finder scope

Naked-eye view

View through finder scope and telescope

Figure 4. The view through a standard finder scope and reflector telescope is rotated 180°. This is true for the AstroView 6 and its finder scope as well.

Aligning the Finder Scope

The AstroView 6 EQ comes with a 6x30 achromatic finder scope (Figure 2a). The number 6 means six-times magnifica- tion and the 30 indicates a 30mm diameter front lens. The finder scope makes it easier to locate the subject you want to observe in the telescope, because the finder scope has a much wider field-of-view.

The AstroView 6 EQ’s finder scope uses a spring-loaded bracket that makes alignment of the finderscope very easy. As you turn either of the thumbscrews, the spring in the bracket’s tensioner moves in and out to keep the finder scope secure in the bracket.

The finder scope must be aligned accurately with the tele- scope for proper use. To align it, first aim the main telescope in the general direction of an object at least a 1/4 mile away-the top of a telephone pole, a chimney, etc. To aim the telescope, loosen the R.A. and Dec. lock levers and move it until it is pointing at the desired object. To help in aiming the telescope, put your eye next to the tube and sight along the length of the optical tube. This will give you a general idea of where the telescope is pointing. Then retighten the R.A. and Dec. lock levers. Turn the focus knob until the object is properly focused. Make sure to position the object in the center of the telescope’s eyepiece by turning the R.A. and declination slow- motion controls.

Now look in the finder scope. Is the object visible? Ideally it will be somewhere in the field of view. If not, some coarse adjust- ment to the finder scope bracket’s thumbscrews will be needed until the object comes into the finder scope’s field of view.

With the image in the finder scope’s field of view, you will now need to fine-adjust the alignment thumbscrews to center the object on the intersection of the crosshairs. Adjust the aim of the finder scope by turning the thumbscrews, one at a time, until the object is centered.

The finder scope alignment needs to be checked before every observing session. This can easily be done at night, before viewing through the telescope. Choose any bright star or planet, center the object in telescope eyepiece, and then

adjust the finder scope bracket’s alignment thumbscrews until the star or planet is centered on the finder’s crosshairs.

Focusing the finder scope

If, when you look through the finder scope, the images appear somewhat out of focus, you will need to refocus the finder scope for your eyes. Loosen the lock ring located behind the objective lens cell on the body of the finder scope (see Figure 2a). Back the lock ring off by a few turns, for now. Refocus the finder scope on a distant object by threading the objec- tive lens cell in or out of the finderscope body. Precise focus- ing will be achieved by focusing the finder scope on a bright star. Once the image appears sharp, retighten the locking ring behind the objective lens cell. The finder scope’s focus should not need to be adjusted again.

Magnification & Eyepieces

Magnification, or power, is determined by the focal length of the telescope and the focal length of the eyepiece. Therefore, by using eyepieces of different focal lengths, the resultant magnification can be varied.

Magnification is calculated as follows:

Telescope Focal Length (mm) Magnification = ———————————————

Eyepiece Focal Length (mm)

The AstroView 6 EQ has a focal length of 750mm, which when used with the supplied 25mm eyepiece yields:

750mm÷25mm=30x

The magnification provided by the 10mm eyepiece is:

750mm÷10mm=75x

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 figure of 50x per inch of aperture is the maximum attainable for most telescopes. Your AstroView 6 EQ has an aperture of 6 inches, so the maximum magnification is about 300x. 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 mag- nification is doubled, an image appears four times dimmer. 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 eye- piece. Then, you may want to increase the magnification to get a closer view. Before changing eyepieces, make sure the object being viewed is centered in the eyepiece field of 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 eye- piece. To change eyepieces, first loosen the thumbscrews on