These knobs make it easy to collimate your Meade 8” f/10 Schmidt-Cassegrain for optimum image quality. You don’t need any tools, so you never have to worry about losing a tiny Allen wrench or screwdriver in the grass in the dark. While it is a long reach, you can probably still adjust the collimation yourself while looking through the eyepiece, so there’s instant feedback about how your optics are performing. Installation of the knobs is a snap with the included instructions, and you can undo the modification at any time. The Bob’s Knobs collimating screws themselves are made of black anodized aluminum alloy. Their knobs are black plastic, 13 mm (1/2”) in diameter. The telescope dust cover will fit on the optical tube with the knobs installed.
Important note: This knob set works only with current 8” f/10 Meade Schmidt-Cassegrain telescopes that have six screws in their secondary mirror housing as shown in the image above. Earlier Meade 8” telescopes have only three screws in the secondary housing. These earlier scopes require knob set #BKM810. The knobs for a six-screw secondary must not be used on older scopes with a three-screw secondary! The screws are too long and can contact the back of the secondary mirror. This knob set must be used only with six-screw Meade secondary versions to avoid possible damage to your optics.
In the six-screw system the three outer screws hold the secondary housing parts together. The three inner screws are for collimation. They hold the secondary mirror and its mounting plate to the secondary housing. The collimation screws, which are threaded into the plate, adjust the mirror tilt (or collimation). There is a coil spring wrapped around each collimation screw between the inside of the housing and the secondary mirror mounting plate.
Do not loosen the factory collimation screws to remove tension before exchanging them with the new collimating knobs. If the original collimation screws are loosened, the coil springs could shift out of place when the factory collimation screws are removed. If that happens, the corrector plate must be pulled and the secondary disassembled to return the springs to their proper location. Should this task become necessary, first note and mark the position of the corrector plate and secondary mirror so they can be re-assembled with the same rotational relationship to the primary mirror.
Bob’s Knobs recommends that you tighten all of the factory collimation screws until the coil springs around them are fully compressed before installing the new Bob’s Knobs. The factory collimation screws are sufficiently tight when they become slightly harder to turn. Do not force the screws beyond this point. Next, remove one collimation screw and replace it with a knob, and repeat this exchange for the remaining two screws, one at a time. By removing only one of the original collimation screws at a time when installing the Bob’s Knobs, the other two firmly-tightened collimating screws will keep pressure on the coil spring you’re working on to keep it from shifting out of place.
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