|STEP 1: Square the Focuser|
Begin by squaring the focuser to the light path. Lay the optical tube on the floor and prop with pillows until a carpenter's level indicates the tube is level. Then, place the level alongside the focuser perpendicular to the length of the optical tube to check alignment. The focuser should be at a 90 degree angle to the tube. If the focuser is seriously out of square, you may see the secondary mirror offset to one side of the optical tube when looking through the focus tube as illustrated at left. Another visual indication of a misaligned focuser is a reflected image of the focus tube in the secondary mirror showing the outside of the tube. The reflected image of the focus tube should only show the circular bottom edge of the tube.
|STEP 2: Center the Secondary Mirror|
The secondary mirror should appear centered within the focus tube as illustrated at left. Looking through the focus tube at the secondary mirror's outline, rack the focuser in-and-out until the primary mirror appears to fill the secondary. The secondary mirror should appear centered within the focus tube. If the secondary appears offset, either toward or away from the primary mirror, move the secondary until it appears centered. Does the secondary look circular in shape. If it has an oval outline, the secondary needs to be rotated until its shape is perfectly circular.
|STEP 3: Center the Primary Mirror|
The primary mirror should appear centered within the secondary mirror. The illustration at left shows this. There should be three or four screws on the backside of the secondary mirror mount. Adjust these screws to change the primary mirror's appearance within the secondary. It's a trial-and-error process. Make small adjustments to one screw and check the effect before moving on to the next screw. Use the retaining clips holding your primary mirror in its cell to define the outside edge of the mirror. There edge of the reflected image of the primary should meet the outside edge of the secondary mirror.
|STEP 4: Center the Image of the Collimation Tool|
The final step is to center the reflected image of the collimation tool. This is done by adjusting collimation screws on the primary mirror cell. As with the screws you adjusted to fine tune the secondary mirror, this is a trial-and-error process. Make a small adjustment to one screw and check the effect. The illustration at left shows the view you get when looking through the focus tube at the secondary mirror of properly collimated Newtonian.
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Revised: February 11, 2002 [WDF]