8 | z |
GETTING STARTED |
CHAPTER |
|
| THE VIEWFINDER |
| |
1 | As with most astronomical telescopes, both ETX model | ||||
telescopes present 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 | ||||
| |||||
| easily center objects in the eyepiece of the main telescope’s | ||||
| field of view.A telescope’s viewfinder is a tremendous aid in the | ||||
| location of faint astronomical objects before observation is | ||||
| made through the telescope’s eyepiece. |
| |||
|
|
| |||
| Standard equipment with the | ||||
| Image Viewfinder has | ||||
| of 21mm. This viewfinder presents a correctly oriented image | ||||
| both |
|
| ||
|
| ||||
| Standard equipment with the | ||||
| Angle Viewfinder has | ||||
| 25mm. This viewfinder presents a correctly oriented image up- | ||||
|
| ||||
| 3 |
|
|
| |
| 2 |
|
|
| |
|
|
|
| 4 |
|
|
|
|
|
| |
|
|
|
|
| |
| 1 | 5 | 3 |
2 | 6 | |
|
|
|
Fig.7: The Viewfinder. (1) Front lens cell; (2) Knurled lock- ring
(6) Rear alignment screws.
Focusing the Viewfinder
Both ETX model viewfinders are factory
ETX-90EC
1.If the viewfinder is mounted in the viewfinder bracket (5,Fig. 7), remove it by slightly unthreading the six alignment screws (4 and 6, Fig. 7) until it can slip easily out of the bracket.
telescope. Gently tighten the six alignment screws. Proceed with Aligning the Viewfinder.
ETX-125EC
Turn the focus ring (2, Fig. 7) at the base of the viewfinder eyepiece (3, Fig. 7) in either direction until a sharp focus is reached.
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 location. To align the viewfinder follow this procedure:
1.The viewfinder bracket (5, Fig. 7) includes six alignment screws (4 and 6, Fig. 7). Turn the three rear alignment screws (6, Fig. 7) so that the viewfinder tube is roughly centered within the viewfinder bracket.
NOTE: Do not overtighten the alignment screws. When tightening one screw it may be necessary to loosen one or both of the two other alignment screws .
2.Using the SP26mm eyepiece, point the main telescope at some
| (before | |
| alignment) | |
| 1 |
|
|
|
|
View through the |
| View through the |
viewfinder |
| telescope eyepiece |
|
|
|
(after
alignment)
2
Fig.8: Aligning the Viewfinder.
3.While looking through the viewfinder, turn one or more of the three front viewfinder alignment screws (4, Fig. 7), until the crosshairs of the viewfinder point at precisely the same position as the view through the eyepiece of the main telescope (2, Fig. 8).
2.Loosen the knurled
3.Look through the viewfinder and focus on a distant object. Slowly rotate the front lens cell in one direction or the other, until the object appears sharp. One or two rotations of the lens may have a significant effect on image focus.
4.Lock the focus in place by threading the knurled
5.Place the viewfinder into the viewfinder bracket on the main
Using the Viewfinder
To locate any object, terrestrial or astronomical, first center the object in the crosshairs of the viewfinder; the object should also then be centered in the field of view of the main telescope.
Observing Tip: If higher observing magnifications are intended, first locate, center, and focus the object using a low- power eyepiece (e.g., SP 26mm eyepiece). Remove the low- power eyepiece and replace it with a