Removing the Optics

Corrector Plate

The corrector plate is held on by the front corrector plate ring. Depending on the age of your telescope, the screws on this ring can be Allen head or Phillip head.

Remove the screws and the retaining ring. Before actually removing the corrector plate, check around the edge of the corrector for an engraved serial number. Use a pencil or other form of marking device to mark the location of this serial number on the backing ring against which the corrector plate rests. This will insure you put the corrector back in its proper orientation.

Also look to see if there are any shims between the corrector plate and the backing ring. Mark the location of these shims as you did the serial number and make sure you know which shim goes where should there be more than one shim. Most of the shims I have seen are small pieces of paper that can easily get lost, so be careful here.

The corrector plate can be removed by grasping the front of the secondary mirror housing and pulling straight out from the tube assembly. It is at the moment the plate pops out of the tube that shims will fly all over the place!

On some scopes it may be necessary to actually pry the corrector plate loose. My present C-8 is one of these. It appears the corrector is not perfectly round and after being pressed into place with the corrector retaining ring, will not come loose by pulling the secondary housing. I use a piece of wood - like a tongue depressor or ice cream stick - to fit into the gap between the tube wall and the plate and pry the corrector GENTLY. Once it has been moved the slightest bit, it comes out easily.

Reassemble in the reverse order. Set the shims in place and align the serial number with the marks you have made on the backing ring. Using the secondary housing as a handle, press the corrector plate gently into place. Set the retaining ring in place and replace the screws. My procedure is to start all screws and turn each until it just starts to tighten up on the retaining ring. Work opposite pairs of screws slowly tight so that the retaining ring is pressing down on the corrector plate with equal pressure around the diameter. Tighten the screws finger tight and do not torque them down! You do not want to exert any distorting pressure against the corrector plate, so be gentle tightening up the screws.

Main Mirror

After the corrector plate has been removed, it will be necessary to remove the focus assembly prior to pulling the main mirror. Refer to the focus assembly disassembly page for how to instructions on pulling the focuser.

Once the corrector and focuser are removed, tip the scope upwards so the main mirror rests at the bottom of the telescope tube. Examine the end of the central tube and you will see a large split ring clip. Remove this clip and the main mirror can be removed from the tube by grasping the mirror mount assembly by the central hub and pulling the whole mirror assembly out of the front of the tube. This hub assembly is secured to the mirror at the factory and it is not recommended you take it apart. Recollimating the scope will probably require returning the instrument to the factory if you remove the mirror itself from the mirror hub assembly.

 

Secondary Mirror

The secondary mirror is mounted in a plastic or aluminum shell at the center of the corrector plate. Older Celestrons used a center screw to hold the secondary mirror in place. The newer models use the collimation screws themselves to hold the mirror. Either unscrew the central screw or the collimation screws to disassemble the secondary.

When reassembling the secondary, you will find an index line on the back of the secondary. This index line must point to the center of the serial number on the corrector plate.

 

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