Meade ETX-125AT, ETX-90AT Focusing the Viewfinder, Aligning the Viewfinder, 1, 3, 7 6, 4 5

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-90AT

1.Remove the viewfinder by slightly unthreading the six alignment screws (4, Fig.

20a) and slipping it out of the bracket.

2.Loosen the knurled lock-ring (2, Fig. 20a) located near the viewfinder’s front lens

cell (1, Fig. 20). 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-105AT or ETX-125AT

Turn the focus ring (6,Fig. 20b) at the base of the viewfinder eyepiece (7, Fig. 20b)

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 (4, Fig. 20a) so that

the viewfinder tube is roughly centered within the viewfinder bracket.

Tip: 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. Point the main telescope at some tall, well-defined land object, such as the top of

a telephone pole. Center the object, as precisely as possible, in the SP 26mm

eyepiece's field of view. Tighten the vertical and horizontal locks (6 and 9,Fig. 1)

so that the tube cannot move and the object remains centered (1,Fig. 21).

3. While looking through the viewfinder, turn one or more of the three front

viewfinder alignment screws (4, Fig. 20a), until the crosshairs of the view-finder

point at precisely the

same position as the

view through the

eyepiece of the main

telescope (2,Fig. 21).

Check 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 or the viewfinder

jarred, the viewfinder

should remain aligned

indefinitely.

Fig.20a: ETX-90 Viewfinder:

(1) Front lens cell;

(2) Knurled lock-ring;

(3) Viewfinder eyepiece;

(4) Alignment screws;

(5) Viewfinder bracket;

Fig.20b: ETX-105/-125

Viewfinder:

(6) Focus ring;

(7) Viewfinder eyepiece

Fig.21: Aligning the Viewfinder.

(before

alignment)

(after

alignment)

View through the

telescope eyepiece

View through the

viewfinder

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