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Old 07-09-2018, 04:09 PM
Dogz (Peter)
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CPC 1100 Secondary mirror removal

I've just pulled my CPC 1100 out of storage after about six years. To my horror I found what I thought was water but later discovered oil on my secondary mirror. After some internet research, I found out that this oil is from grease that resides behind the secondary mirror. I've managed to remove the corrector plate and then the secondary mirror cell for cleaning. So far I've managed to remove the oil and about 90% of the blemishes on the mirror, using isopropyl alcohol water and soap mix.
Now to complete the job I wish to remove the secondary mirror from it's cell. To do this I presume I just remove the collimation screws. My question is what will I find when I do and how hard will it be to put back together again and what grease should I use as a replacement? While the mirror is out of it's plastic housing I will give acetone ago at removing the last of the blemishes from the mirror.
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Old 08-09-2018, 08:13 AM
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multiweb (Marc)
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It's possible to get a little oil on the inside of the corrector from the baffle tube if stored vertically. I sotore mine vertically pointing up for that reason. I did a little wood rig for it. No drama a at all. Easily cleaned.

You should see a black line at the back of your secondary. That should point towards the focuser knob side when looking at the front of the scope. The three collimation screws hold the primary on its central pivot point. Just make it as level as you can without tightening it too much and finish collimation when it's back in place.

There should be some rubber/cork gaskets between the glass and the secondary cell as well so you don't pinch the corrector glass too hard.

Put the corrector back in place the way you've found it, facing out and same orientation with same shim positions.
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Old 12-09-2018, 10:44 PM
Dogz (Peter)
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Thank you for the valuable information the disassembly went well and the mirror cleaned up like new. I've replaced the grease, with just the bare minimum. I used high temperature axle grease, that's all I had anyway and it's red just like the stuff that leaked out.

But I need clarification on the direction of the black line. If I hold the mirror so that it's facing into the telescope the black line can only face the focuser knob side (my left) at the 7 or 11 o'clock. It could however face away from the focuser at 3 o'clock. Or should I be placing the black line pointing at the focuser when I'm looking at both the mirror surfaces.

Thanx again Peter

Just a after thought on this. When the scope was new the secondary cell was loose and it was repaired under warranty and was tightened so that the Celestron label was horizontal. Was this correct ??

Last edited by Dogz; 13-09-2018 at 01:07 AM.
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Old 13-09-2018, 05:34 PM
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multiweb (Marc)
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The label being horizontal makes sense. Do you have any pictures of the rig?
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Old 13-09-2018, 08:18 PM
Dogz (Peter)
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I rang Bintel today for advice and the tech there told me that with my scope being around 10 yrs old it should have a serial number etched into the glass near the edge. The line should point to that. If not it's a Chinese model and I'm stuck with trial and error.

At first I couldn't see any serial number at all. But after searching with a magnifying glass I found it under a black mark I made marking the shim positions. The line now points to 3 o'clock with the label just off horizontal.

When the weather clears I'll give it a star test and let you know how it went.

Thanx again for your help
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