Aligning the Finder Scope, Focusing the Finder Scope

Aligning the Finder Scope

The SkyView Pro 80mm ED EQ comes with a 8x40 achromat- ic finder scope (Figure 3a). The number 8 means eight-times magnification and the 40 indicates a 40mm diameter front lens. The finder scope makes it easier to locate the object you want to observe in the telescope, because the finder scope has a much wider field-of-view.

The finder scope uses a spring-loaded bracket that makes alignment of the finderscope very easy. As you turn either of the thumb screws, 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 at an object at least a 1/4 mile away - the top of a telephone pole, a chimney, etc. First loosen the R.A. and Dec. lock levers and move the telescope until it is pointing towards the desired object.Then sight along the tube to precisely aim the telescope. Turn the focus knob until the object is properly focused. Make sure to position the object in the center of the telescope’s eye- piece by turning the R.A. and declination slow-motion control knobs (the R.A. and Dec. lock levers must be tightened to use the slow-motion control knobs).

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 alignment thumb screws 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 now need to fine-adjust the alignment thumb screws to center the object on the intersection of the crosshairs. Adjust the aim of the finder scope by turning the thumb screws, one at a time, until the object is centered. Make sure the object is still cen- tered in the telescope’s eyepiece as well. If it isn’t, you will need to repeat the entire process.

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 plan- et, center the object in telescope eyepiece, and then adjust the finder scope bracket’s alignment thumb screws 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 3a). Back the lock ring off by a few turns, for now. Refocus the finder scope on a distant object by threading the objective lens cell in or out of the finder scope body. Precise focusing will be achieved by focusing the finder scope on a bright star. Once the image appears sharp, retighten the lock 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:

Magnification= Telescope Focal Length (mm)

Eyepiece Focal Length (mm)

The SkyView Pro 80mm ED EQ has a focal length of 600mm, which when used with the supplied 25mm eyepiece yields:

600 mm = 24x

25 mm

The magnification provided by the 10mm eyepiece is:

	600 mm	= 60x
	10 mm	= 60x
	10 mm

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 2x per millimeter of aperture is the maximum attain- able for most telescopes. Your SkyView Pro 80mm ED EQ has an aperture of 80 millimeters, so the maximum magnification would be about 160x. 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 fac- tor 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 increase the magnification to get a closer view, if you wish. 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 thumb screw on the 1.25" adapter on the star diagonal. 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 target. Replace the eyepiece with the new one by sliding it gently into the holder. Re-tighten the thumb screw, and refocus for your new magnification.

Use of 2" Eyepieces

A feature of the SkyView Pro 80mm ED EQ is its ability to use either 1.25" or 2" barrel-diameter eyepieces. At low magnifica- tions, 2" eyepieces can give a wider field of view than standard 1.25" eyepieces. This is especially desirable for observing deep-sky objects, as many of them appear quite large, but