Celestron OMNI XLT 102 manual Collimated telescope Should appear Symmetrical with

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Before you begin the collimation process, be sure that your telescope is in thermal equilibrium with the surroundings. Allow 45 minutes for the telescope to reach equilibrium if you move between large temperature extremes.

To verify collimation, view a star near the zenith. Use a medium to high power ocular — 12mm to 6mm focal length. It is important to center a star in the center of the field to judge collimation. Slowly cross in and out of focus and judge the symmetry of the star. If you see a systematic skewing of the star to one side, then re-collimation is needed.

Figure 7-4

Even though the star pattern appears the same on both sides of focus, they are asymmetric. The dark obstruction is skewed off to the left side of the diffraction pattern indicating poor collimation.

To accomplish this, you need to tighten the secondary collimation screw(s) that move the star across the field toward the direction of the skewed light. These screws are located in the secondary mirror holder (see figure 7-3). Make only small 1/6 to 1/8 adjustments to the collimation screws and re-center the star by moving the scope before making any improvements or before making further adjustments.

To make collimation a simple procedure, follow these easy steps:

1.While looking through a medium to high power eyepiece, de-focus a bright star until a ring pattern with a dark shadow appears (see figure 7-4). Center the de-focused star and notice in which direction the central shadow is skewed.

2.Place your finger along the edge of the front cell of the telescope (be careful not to touch the corrector plate), pointing towards the collimation screws. The shadow of your finger should be visible when looking into the eyepiece. Rotate your finger around the tube edge until its shadow is seen closest to the narrowest portion of the rings (i.e. the same direction in which the central shadow is skewed).

3.Locate the collimation screw closest to where your finger is positioned. This will be the collimation screw you will need to adjust first. (If your finger is positioned exactly between two of the collimation screws, then you will need to adjust the screw opposite where your finger is located).

4.Use the hand control buttons to move the de-focused star image to the edge of the field of view, in the same direction that the central obstruction of the star image is skewed.

Figure 7-5

A collimated telescope

should appear

symmetrical with the

central obstruction centered in the star's diffraction pattern.

5.While looking through the eyepiece, use an Allen wrench to turn the collimation screw you located in step 2 and 3. Usually a tenth of a turn is enough to notice a change in collimation. If the star image moves out of the field of view in the direction that the central shadow is skewed, than you are turning the collimation screw the wrong way. Turn the screw in the opposite direction, so that the star image is moving towards the center of the field of view.

6.If while turning you notice that the screws get very loose, then simply tighten the other two screws by the same amount. Conversely, if the collimation screw gets too tight, then loosen the other two screws by the same amount.

7.Once the star image is in the center of the field of view, check to see if the rings are concentric. If the central obstruction is still skewed in the same direction, then continue turning the screw(s) in the same direction. If you find that the ring pattern is skewed in a different direction, than simply repeat steps 2 through 6 as above for the new direction.

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Contents Omni XLT Series Telescopes Table of Contents Astrophotography Page Omni XLT 102 Refractor Omni XLT 150 Newtonian Omni XLT 127 Schmidt-Cassegrain Setting up the Tripod Attaching the Equatorial Mount Attaching the Center Leg Brace Installing the Counterweight BarAttaching the Slow Motion Control Knobs Cables Installing the CounterweightsAttaching the Telescope Tube to the Mount Installing the Visual Back Installing the FinderscopeInstalling the Eyepieces Installing the Star DiagonalBalancing the Mount in R.A Moving the Telescope ManuallyBalancing the Mount in DEC Adjusting the MountAdjusting the Mount in Azimuth Adjusting the Mount in AltitudePage Page Image Orientation FocusingCalculating Magnification Aligning the FinderscopeGeneral Observing Hints Determining Field of ViewCelestial Coordinate System Motion of the Stars Pointing at Polaris Latitude ScaleFinding the North Celestial Pole Polar Alignment with the Latitude Scale Polar Alignment in the Southern HemisphereFinding the South Celestial Pole SCP Pointing at Sigma OctantisDeclination Drift Method of Polar Alignment Aligning the R.A. Setting Circle 11 Vernier Scale Using the R.A. Vernier ScalePlanetary Observing Hints Observing the MoonLunar Observing Hints Observing the PlanetsSeeing Conditions Observing the SunSolar Observing Hints Observing Deep Sky ObjectsSeeing Using the Lens Cap Aperture Stop with Refractor TelescopesPiggyback Photography Using Digital Cameras Full Eyepiece Projection for a Schmidt-CassegrainLong Exposure Prime Focus Photography Planetary and Lunar Photography with Special Imagers Reducing Vibration CCD Imaging for Deep Sky ObjectsTerrestrial Photography MeteringCollimation of Refractors Care and Cleaning of the OpticsTwo 2 turns Collimation of a Schmidt-CassegrainCollimated telescope Should appear Symmetrical with Aligning the Secondary Mirror Collimation of a NewtonianBoth mirrors aligned with your eye looking into the focuser Night Time Star Collimating As a Series 1 # Page Page Appendix a Technical Specifications Appendix B Glossary of Terms Page Page Page Page Page Page Page Page Celestron Two Year Warranty
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