These knobs make it easy to collimate your Meade 8” f/6.3 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 are made of stainless steel. Their knobs are also stainless steel, 12 mm (1/2”) in diameter.
Important note: This knob set works with all 8” f/6.3 Meade Schmidt-Cassegrain telescopes, such as the LX5, LX6, Premier, LX100, LX200, etc. These scopes were also available in an f/10 focal ratio. These particular knobs work only with the f/6.3 versions of these scopes, and are not for the f/10 models. Meade has re-designed the secondary mirror assembly on their 8” SCT with six screws instead of three screws that appear on the older design. The three outer screws hold the secondary housing parts together, and the three inner screws are for collimation. Knobs for the 6-screw secondary must not be used on scopes with the 3-screw secondary! The screws are too long and they can contact the back of the secondary mirror.
Since the factory dust cover contacts the secondary housing when you put it on the scope for storage, additional clearance is needed to make room for the knobs. The knobs come with a set of spacers that attach to the inside of the dust cover to move it slightly away from the secondary assembly so the dust cover will clear the knobs. You can also press the center of the lightweight aluminum cover outward from the inside with your thumbs to contour it for additional clearance.
The three collimation screws hold the secondary mirror and its mounting plate to the secondary housing. The mirror mounting plate pivots on a tang or spring at its center, and the collimation screws, which are threaded into the plate, adjust the mirror tilt (or collimation). Do not remove more than one of the original collimation screws at a time when installing Bob's Knobs, as the secondary mirror might fall off (if all three screws are removed at the same time), or the secondary can pivot inside the tube, scratching the corrector plate (if two screws are removed simultaneously). By removing only one factory collimation screw at a time, replacing it with a knob, and repeating this process for the other two collimation screws, there's no danger of dropping the secondary mirror. The instructions also recommend pointing the optical tube assembly slightly downward during the installation of the knobs for an added safety measure.
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