Meade 50 AZ-T instruction manual Viewfinder, Magnification

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4. Primary Mirror Adjustments

If the secondary mirror and the reflection of the primary mirror (1), Fig. 8, appear centered within the drawtube (2), Fig. 8, but the reflection of your eye (3), Fig. 8, appears off-center, one or more of the three primary mirror hex screws of the primary mirror cell will need to be adjusted. These primary hex screws are located behind the primary mirror, at the lower end of the main tube. Adjust the primary mirror alignment by slightly turning one hex screw at a time, looking through the focuser after each adjustment to determine if the mirror is moving in the correct direction.

THE VIEWFINDER

The Starfinder telescope, as with almost all astronomical telescopes, presents a fairly narrow field of view to the observer. As a result, it is sometimes difficult to locate and center objects in the telescope’s field of view .

The viewfinder, by contrast, is a low-powered, wide-field sighting scope with crosshairs that enables the easy centering of objects in the main telescope’s field of view. Standard equipment with the Starfinder telescope is a viewfinder of 8-power and 50mm aperture, called an “8 x 50mm viewfinder.”

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1

3

4

Fig. 9: 8 x 50mm Viewfinder. (1) Rear-most Alignment Screws;

(2)Front-most Alignment Screws; (3) Viewfinder Focus Lock Ring;

(4)Mounting Bracket.

Focusing the Viewfinder

The viewfinder has been factory prefocused to objects located at infinity. Individual eye variations, however, may require that the viewfinder be refocused to your eye. Looking through the viewfinder, point the telescope at a distant object; if the viewfinder image is not sufficiently in focus for your eye, it may be refocused as follows:

1.Remove the viewfinder from its mounting bracket (4), Fig. 9, by slightly unthreading the six alignment screws until the viewfinder can slip out easily.

2.Loosen the viewfinder focus lock ring (3), Fig. 9, at the objective-lens-end of the viewfinder, enabling rotation of the objective lens cell clockwise or counterclockwise for precise focusing while looking at a distant object through the viewfinder.

3.After a precise focus has been achieved, tighten the viewfinder focus lock ring against the objective lens cell to lock the focus in place.

4.Replace the viewfinder into its bracket on the main telescope.

Note: No focusing is possible from the eyepiece end of the viewfinder.

Aligning the Viewfinder

In order for the viewfinder to be useful, it must first be aligned with the main telescope, so that both the viewfinder and the main telescope are pointing at precisely the same place. To align the viewfinder, follow this procedure:

1.The viewfinder bracket (4), Fig. 9, includes six alignment screws. Turn the three rear-most alignment screws (1), Fig. 9, so that the viewfinder tube is roughly centered within the viewfinder bracket, as viewed from the eyepiece-end of the telescope.

2.Using the standard equipment 25mm eyepiece, point the main telescope at some easy-to-find, well-defined land object, such as the top of a telephone pole. Center the object precisely in the main telescope's field.

3.While looking through the viewfinder, gently turn one or more of the three front-most viewfinder alignment screws (2), Fig. 9, until the crosshairs of the viewfinder point at precisely the same position as the main telescope. During this procedure, occasionally look through the main telescope to make sure the object is still centered.

When the object is centered in the viewfinder, confirm that the viewfinder's crosshairs and the main telescope are now pointing at precisely the same object. The viewfinder is now aligned to the main telescope. Unless the alignment screws are disturbed, the viewfinder will remain aligned indefinitely.

Using the Viewfinder

Now, to locate any object, terrestrial or astronomical, first center the object on the crosshairs of the viewfinder; the object will then be centered in the field of the main telescope.

Note: If higher observing magnifications are to be utilized, first locate, center, and focus the object using a low-power eyepiece (e.g., the 25mm eyepiece). Objects are easier to locate and center at low powers; higher power eyepieces may then be employed by changing eyepieces.

MAGNIFICATION

The magnification, or power, at which a telescope is operating is determined by two factors: the focal length of the eyepiece employed and the focal length of the telescope. The Meade Starfinder telescope is supplied with one eyepiece as standard equipment. The focal length of the eyepiece, 25mm, is printed on its side.

Telescope focal length is, roughly speaking, the distance that light travels inside the telescope before reaching a focus.

The focal length of the Starfinder 16” f/4.5 = 1830mm.

On a given telescope, such as the Starfinder, different eyepiece focal lengths are used to achieve different magnifications, from low to high. Optional eyepieces and the #140 2x Barlow Lens are available for powers from 36x to over 500x (see Optional Accessories, page 11).

To calculate the magnification obtained with a given eyepiece, use this formula:

Telescope Focal Length

Power = ___________________

Eyepiece Focal Length

Example: Using the 25mm eyepiece supplied with the 16" f/4.5, the power is:

1830mm

Power = _______ = 73x

025mm

The most common mistake of the beginning observer is to “overpower” the telescope and use high magnification which the telescope’s aperture and typical atmospheric conditions cannot reasonably support. Keep in mind that a smaller, but bright and well-resolved, image is far superior to a larger, but dim and poorly resolved, one. Powers above about 300x should be employed with the Starfinder telescope only under the steadiest atmospheric conditions.