Meade Telescope, LXD 75 instruction manual Aligning the Viewfinder, Choosing an Eyepiece

Collimation Screws

Viewfinder

Eyepiece

Viewfinder

Bracket

Fig. 14a: Viewfinder assembly, refractor and Schmidt-Newtonian mod-

Collimation Screws	Viewfinder
	Eyepiece

Viewfinder

Bracket

Fig. 14b: Viewfinder assembly, Newtonian models.

Important Note: Objects appear upside-down and reversed left-for-right when observed in the viewfinder. With refracting telescope models, objects viewed through the main telescope with the diagonal mirror in place are seen right-side-up, but reversed left-for-right.

This image inversion is of no consequence when observ- ing astronomical objects, and in fact all astronomical telescopes yield inverted images.

During terrestrial observing, where a fully-correctly-orient- ed image (right-side up and correct left-for-right) is desir- able, an optional Meade #928 45° Erect-Image Diagonal Prism is available. See OPTIONAL ACCES- SORIES, page 38.

Note that for Schmidt- Newtonian models, no means of image inversion is available; while these tele- scopes may be used for ter- restrial observing, the image will not be correctly oriented in either right-side-up or left- for-right orientations.

3.Achromatic refractor, Schmidt-Newtonian models and Newtonian models: Again, hold the optical tube so that it cannot accidentally swing freely. Lock the R.A. lock (33, Fig. 1d), and unlock the Dec. lock (17, Fig. 1d). The telescope now is able to move freely about the Dec. axis. Loosen the cradle ring lock knobs (13, Fig. 1a) so that the main tube slides easily back and forth in the cradle rings. Move the main tube in the cradle rings until the telescope remains in one posi- tion without tending to drift down in either direction. Re-lock the Dec. lock (17, Fig. 1d).

The telescope is now properly balanced on both axes. Next, the viewfinder must be aligned.

Aligning the Viewfinder

The wide field of view of the telescope's viewfinder (4, Fig. 1a) provides an easier way to initially sight objects than the main telescope's eyepiece (3, Fig. 1a), which has a much narrower field of view. If you have not already attached the viewfinder to the tel- escope tube assembly, follow the procedure described in step 9, page 12.

In order for the viewfinder to be useful, it must be aligned to the main telescope, so that both the viewfinder and telescope's optical tube (10, Fig. 1a) point at the same position in the sky. This alignment makes it easier to find objects: First locate an object in the wide-field viewfinder, then look into the eyepiece of the main telescope for a detailed view.

To align the viewfinder, perform steps 1 through 4 during the daytime; perform step 5 at night. Both the 6 x 30mm and the 8 x 50mm viewfinders align in an identical man- ner. Refer to Figs. 14a and 14b.

1.Remove the dust covers from the optical tube (9, Fig. 1a) and the viewfinder.

2.If you have not already done so, insert the low-power SP 26mm eyepiece (3, Fig. 1b) into the eyepiece holder of the main telescope. See step 10, page 12.

3.Look through the viewfinder eyepiece at an object at least one-half mile away (Tip: Remove the viewfinder tube from the bracket to simplify this operation). If the distant object is not in focus, turn the focus lock ring counterclockwise to loosen the viewfinder front cell (6, Fig. 1b). Twist the front cell until focus is achieved and retighten the focus lock ring.

4.Unlock the R.A. lock (33, Fig. 1d) and the Dec lock (17, Fig. 1d) so that the tel- escope turns freely on both axes. Then point the main telescope at a tall, well- defined and stationary land object (e.g., the top of a telephone pole) at least 200 yards distant and center the object in the telescope's eyepiece. Focus the image by turning the focus knobs (8, Fig. 1b). Retighten the R.A. and Dec. locks.

5.Look through the viewfinder and loosen or tighten, as appropriate, one or more of the viewfinder collimation thumbscrews (5, Fig. 1b) until the viewfinder’s crosshairs are precisely centered on the object you previously centered in the main telescope's eyepiece. You are now ready to make your first observations with your telescope.

NEVER point the telescope directly at or near the Sun at any time! Observing the Sun, even for the smallest fraction of a second, will result in instant and irreversible eye damage, as well as physical damage to the telescope itself.

5.Check this alignment on a celestial object, such as a bright star or the Moon, and make any necessary refinements, using the method outlined above in steps 3 and 4.

With this alignment performed, objects first located in the wide-field viewfinder will also appear in the telescope's eyepiece.

Choosing an Eyepiece

A telescope’s eyepiece magnifies the image formed by the telescope’s main optics. Each eyepiece has a focal length, expressed in millimeters, or “mm.” The smaller the focal length, the higher the magnification. For example, an eyepiece with a focal length of 9mm has a higher magnification than an eyepiece with a focal length of 26mm.

Your telescope comes supplied with a Super Plössl (SP) 26mm eyepiece which gives a wide, comfortable field of view with high image resolution.

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