Celestron OMNI XLT 102 manual Image Orientation, Focusing

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Image Orientation

The image orientation changes depending on how the eyepiece is inserted into the telescope. When using the star diagonal with refractors and Schmidt-Cassegrains, the image is right-side-up, but reversed from left-to-right (i.e., mirror image). If inserting the eyepiece directly into the focuser of a refractor or the visual back of the Schmidt- Cassegrain (i.e., without the star diagonal), the image is upside-down and reversed from left-to-right (i.e., inverted).

Newtonian reflectors produce a right-side-up image but the image will appear rotated based on the location of the eyepiece holder in relation to the ground. Newtonian reflectors are best for astronomical use where right-side-up does not matter.

Actual image orientation as seen

with the unaided eye

Focusing

Reversed from left to right, as

viewed using a Star Diagonal on a refractor or Schmidt-Cassegrain

Figure 3-4

Inverted image, normal with Newtonians and as viewed with eyepiece directly in other scopes

To focus your refractor or Newtonian telescope, simply turn the focus knob located directly below the eyepiece holder. Turning the knob clockwise allows you to focus on an object that is farther than the one you are currently observing. Turning the knob counterclockwise from you allows you to focus on an object closer than the one you are currently observing.

The Schmidt-Cassegrain focusing mechanism controls the primary mirror which is mounted on a ring that slides back and forth on the primary baffle tube. The focusing knob, which moves the primary mirror, is on the rear cell of the telescope just below the star diagonal and eyepiece. Turn the focusing knob until the image is sharp. If the knob will not turn, it has reached the end of its travel on the focusing mechanism. Turn the knob in the opposite direction until the image is sharp. Once an image is in focus, turn the knob clockwise to focus on a closer object and counterclockwise for a more distant object. A single turn of the focusing knob moves the primary mirror only slightly. Therefore, it will take many turns (about 30) to go from close (near) focus to infinity.

For astronomical viewing, out of focus star images are very diffuse, making them difficult to see. If you turn the focus knob too quickly, you can go right through focus without seeing the image. To avoid this problem, your first astronomical target should be a bright object (like the Moon or a planet) so that the image is visible even when out of focus. Critical focusing is best accomplished when the focusing knob is turned in such a manner that the mirror moves against the pull of gravity. In doing so, any mirror shift is minimized. For astronomical observing, both visually and photographically, this is done by turning the focus knob counterclockwise.

Figure 3-5

The emblem on the end of the focus knob shows the correct rotational direction for

focusing your telescope.

Note: If you wear corrective lenses (specifically glasses), you may want to remove them when observing with an eyepiece attached to the telescope. However, when using a camera you should always wear corrective lenses to ensure the sharpest possible focus. If you have astigmatism, corrective lenses must be worn at all times.

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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 Installing the Counterweight Bar Attaching the Center Leg BraceInstalling the Counterweights Attaching the Slow Motion Control Knobs CablesAttaching the Telescope Tube to the Mount Installing the Finderscope Installing the Visual BackInstalling the Star Diagonal Installing the EyepiecesMoving the Telescope Manually Balancing the Mount in R.AAdjusting the Mount Balancing the Mount in DECAdjusting the Mount in Altitude Adjusting the Mount in AzimuthPage Page Focusing Image OrientationAligning the Finderscope Calculating MagnificationDetermining Field of View General Observing HintsCelestial Coordinate System Motion of the Stars Latitude Scale Pointing at PolarisFinding the North Celestial Pole Polar Alignment in the Southern Hemisphere Polar Alignment with the Latitude ScalePointing at Sigma Octantis Finding the South Celestial Pole SCPDeclination Drift Method of Polar Alignment Aligning the R.A. Setting Circle Using the R.A. Vernier Scale 11 Vernier ScaleObserving the Moon Lunar Observing HintsObserving the Planets Planetary Observing HintsObserving the Sun Solar Observing HintsObserving Deep Sky Objects Seeing ConditionsUsing the Lens Cap Aperture Stop with Refractor Telescopes SeeingPiggyback Photography Using Digital Cameras Eyepiece Projection for a Schmidt-Cassegrain FullLong Exposure Prime Focus Photography Planetary and Lunar Photography with Special Imagers CCD Imaging for Deep Sky Objects Terrestrial PhotographyMetering Reducing VibrationCare and Cleaning of the Optics Collimation of RefractorsCollimation of a Schmidt-Cassegrain Two 2 turnsCollimated telescope Should appear Symmetrical with Collimation of a Newtonian Aligning the Secondary MirrorBoth 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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