Meade LXD 75-Series instruction manual

Note: A small paper ring is attached to the primary mir- ror. This ring was attached at the factory for purposes of laser collimation. The ring will not diminish your tele- scope's imaging capabilities and does not need to be removed.

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Fig. 32: Correct (1) and incorrect (2) collimation as viewed during a star test.

4.Perform an actual star test to confirm the accuracy of steps 1 through 3. Using the SP 26mm eyepiece, point the telescope at a moderately bright (second or third mag- nitude) star, and center the image in the main telescope's field of view.

5.Bring the star's image slowly in and out of focus until you see several disks sur- rounding the star's center. If steps 1 through 3 were done correctly, you will see con- centric (centered with respect to each other) circles (1, Fig. 32).

An improperly collimated instrument will reveal oblong or elongated circles (2, Fig. 32). Adjust the 3 collimating screws on the primary mirror housing until the circles are concentric on either side of the focus.

In summary, the 4 adjustment screws on the plastic diagonal mirror housing change the tilt of the secondary mirror so that it is correctly centered in the focuser draw- tube, and so that the primary mirror appears centered when looking into the focuser. The 3 collimating knobs on the primary mirror change the tilt of the primary mirror so that it reflects the light directly up the center of the drawtube.

Alignment (Collimation) of the Schmidt-Cassegrain Optical System

The optical collimation (alignment) of any astronomical telescope used for serious purposes is important, but in the case of the Schmidt-Cassegrain design of the model SC-8, such collimation is absolutely essential for good performance. Take special care to read and understand this section well so that your model SC-8will give you the best optical performance.

As part of final optical testing, every Meade Schmidt-Cassegrain is precisely colli- mated at the Meade factory before shipment. However, vibrations in shipping can cause the optical system to become misaligned. Re-aligning the optics is, however, a straightforward process.

To check the collimation of your SC-8, center a bright star that is overhead, or use a “hot spot” of reflected Sunlight from a chrome car bumper, with the supplied 26mm eyepiece. Allow the telescope to adjust to the temperature of your observation site before proceeding; temperature differences between the optics and the outside air can cause distortion in the images.

With the star or hot spot centered, de-focus the image. You will notice that the out of focus star image looks like a ring of light surrounding a dark central spot; the dark cen- tral spot is in fact the shadow of the secondary mirror. Turn the focus knob until the ring of light fills about 10% of the eyepiece field-diameter. If the dark central spot is offset in (i.e., not concentric with) the ring of light, your telescope’s optical system is misaligned and requires collimation.

Follow these steps for collimation of the optical system:

a.The only adjustments possible, or necessary, on the SC-8 models are from the three screws (Fig. 33b) located at the edge of the outer surface of the secondary mirror housing.

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