Meade ETX-125EC, ETX-105EC Using The Viewfinder, Focusing the Viewfinder, Aligning the Viewfinder

Using The Viewfinder

As with most astronomical telescopes, the 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 low-power, wide-field sighting scope with crosshairs that let you easily center objects in the eyepiece of the main telescope’s field of view. The telescope viewfinder is a great help in locating faint astronomical objects before you begin observing through the telescope eyepiece.

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ETX-90EC Viewfinder

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ETX-105EC/-125EC Right-Angle Viewfinder

Fig. 5: Viewfinder Installation.

ETX-90EC 8 x 21mm Erect-Image Viewfinder:

Standard equipment with the ETX-90EC, the 8 x 21mm Erect-Image Viewfinder has 8-power magnification

and an aperture of 21mm. This viewfinder presents a correctly oriented image both up-and-down and left-to-right.

ETX-105EC or ETX-125EC 8 x 25mm Right-Angle Viewfinder:

Standard equipment with the ETX-105EC and ETX-125EC, the 8 x 25mm Right-Angle Viewfinder has 8-

power magnification and an aperture of 25mm. This viewfinder presents a correctly oriented image up- and-down, but is reversed left-for-right.

Focusing the Viewfinder

The ETX model viewfinders are pre-focused at the factory. Individual eye variations may require that the viewfinder be re-focused. To check the focus, point the viewfinder at a distant terrestrial (land) object such as a telephone pole or light pole and look through the viewfinder. If the viewfinder image is not in sharp focus, follow the procedure below that applies to your telescope model.

ETX-90EC

1.Remove the viewfinder by slightly unthreading the six alignment screws (4 and 6, Fig. 6) and slipping it out of the bracket.

2.Loosen the knurled lock-ring (2, Fig. 6) located near the viewfinder’s front lens cell (1, Fig. 6). Unthread this ring (counterclockwise, as seen from the eyepiece-end of the viewfinder) by several turns.

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 lock-ring clockwise up against the viewfinder’s lens cell.

5.Replace the viewfinder into the viewfinder bracket. Gently tighten the six alignment screws. Proceed with Aligning the Viewfinder.

ETX-105EC or ETX-125EC

Turn the focus ring (2, Fig. 6) at the base of the viewfinder eyepiece (3, Fig. 6) 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:

1.Turn the three rear alignment screws of the viewfinder bracket (6, Fig. 6) so that the viewfinder tube is roughly centered within the viewfinder bracket.

Tip: Do not overtighten the align- ment screws. When tightening one screw it may be necessary to loosen one or both of the two other alignment screws.

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2
		4
ETX-125EC
	1	5	3
ETX-90EC	2		6

Fig. 6: The Viewfinder. (1) Front lens cell; (2) Knurled lock- ring (ETX-90EC) or focus ring (ETX-105EC and ETX- 125EC); (3) Viewfinder eyepiece; (4) Front alignment screws (one not visible in photo); (5) Viewfinder bracket; (6) Rear alignment screws (one not visible).

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