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I have a Celestron CPC 1100 which lives outside in an obsy and I must admit I do store it with the corrector plate facing downwards and a scope cover over the set-up. For a while now I have been living with a smear on the inside of the corrector plate. It looks like a clear gel that has dripped onto the plate near the centre then run down to the edge and set.

This smear shows up clearly as a spike on the diffraction disc but last night when doing a star test there was another larger area where the diffraction rings were deformed. When I took the visual back off and looked down the tube I could see that the bottom quarter of the secondary mirror was also 'gunged up'.

The only possible cause I can think of is that lubricating grease from primary mirror slide tube has dripped onto the inside of the corrector plate and the secondary mirror.

I very occasionally put a fan heater on inside the obsy to help dry it out after a particulary dewy night. I also use a cool hair drier to remove dew. I don't have any dew control system. Sorry to ramble on but I would appreciate help with;

(a) is this likely to be lubricating grease from the slide tube?

(:) if so why has it started dripping onto the corrector plate (the scope is just over 2 years old)?

© I will now store the scope with the tube horizontal, are there any other precautions?

(d) Any suggestions what solvent I should use to remove it (I have the Baader Wonder fluid).

This might also be a cautionary tale for other SCT owners.

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The grease is two fold as far as I have been led to believe.A lubricant, obviously, but also as a buffer between the the Baffle tube, and the mirror sleeve which slides up and down the baffle when focusing.

It pays to take the mirror right up to the top, and back down again occasionally, to distribute the grease evenly up the tube. This can reduce mirror flop, which can occur in SCT's

Inverting the tube when it is not in use for long periods, can lead to the problem you describe. I invert mine too, but not entirely perpendicular, I leave it about 25 degrees.

If there is a lot of gunge on the mirror, I would advocate a complete strip down and clean. Of course you need to take advice from those who have already done this operation, and take great care, especally removing the corrector plate, and taking the mirror out too.

Ron.

Edited by barkis
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If there is a lot of gunge on the mirror, I would advocate a complete strip down and clean.

Probably no choice :) Good luck!

The best scheme seems to be to store the tube pointed down at about 45 degrees, so any drips hit the inside of the tube rather than the corrector or, even worse, the secondary. Horizontal is not good because the grease can run from the baffle tube straight down the primary mirror.

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Probably no choice ;) Good luck!

The best scheme seems to be to store the tube pointed down at about 45 degrees, so any drips hit the inside of the tube rather than the corrector or, even worse, the secondary. Horizontal is not good because the grease can run from the baffle tube straight down the primary mirror.

I would have thought that if there was any grease going to run down the mirror when horizontal it would also run down it at 45˚.

Probably best to leave it pointing up at 30˚ :)

Allan

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I would have thought that if there was any grease going to run down the mirror when horizontal it would also run down it at 45˚.

No, it will run "up" the baffle tube, drip off the end and fall onto the inside of the tube.

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Hmmm

I've been using SCT's on and off for the last 20 years and I've never experienced grease melting and dripping from the baffle tube. It's usually very thick and sticky.

I'm wondering if something has dripped in and through/ from the eyepiece aperture?

Check with a torch on the INSIDE of the baffle tube ( remove the rear cell eyepiece adaptors) see if there's any trace of the stuff in there.

Ken

ps How old is the scope? I'd also check with the supplier.... these telescopes should last a lifetime.

Edited by Merlin66
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Thanks all. The scope is only just over 2 years old. I've checked the inside of the eyepiece aperture and nothing has, or could have, dripped in from there. I'm absolutely sure trhat whatever has dripped onto the corrector plate and secondary has come from inside the tube. I have put in a query to Celestron technical help so will let you know if they come up with anything useful. Busy reading up on how to remove the corrector plate - plenty of good advice here and elsewhere on the web. Sounds like a good way of finding out how long you can hold your breath. I also like the idea of moving the mirror fully back and forth to re-distribute the grease on the slider.

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Is it coincidence that all the respondents seem to have Celestron SCT's

Possibly not, the problem seems to be isolated to newer tubes manufactured in China - the US made ones presumably used a better grease. If Meade's Mexican plant starts using Chinese grease, expect problems.

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Goodness me.

Horrible, just horrible. :)

I've seen a tub of grease that lived in my dads garage that had seperated so to speak. There was a liquidy pool on top of the rest. But I'm sure it was just a general usage grease. I must say I would have thought that a more specialist grease would have been use in scopes etc.

Looks like a strip down job will be necessary ;)

Andy

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Apparantly the lubricating grease used can separate and the lighter oil drip off the baffle. Got the following reply from Celestron;

"1- its lubricating grease used in the baffle tube.

Use a can of compressed air (like those used for cleaning computer keyboards or cameras) to get the loose dust off first. Mix a solution of 50/50 isopropyl alcohol (rubbing alcohol from a drug store) and distilled water. Apply the solution to a oil free tissue and wipe with little to no downward pressure in straight strokes across the surfaces while rotating the tissue to lift the dust off the lens.

For the primary main lens of mirror of the scope, use a white unscented Kleenex. Folded into a small square. Again, wipe in straight strokes and lift the Kleenex as you wipe to lift the dirt off. Discard Kleenex. Repeat. Do not attempt to disassemble the lenses of the scope or eyepieces in order to clean the inside. If the scope or eyepieces require internal cleaning, it is best to have this done professionally by sending it to the factory for service. "

They also recommended storing the scope with the tube horizontal. Definitely going to take the corrector plate off (very, very carefully) to clean the mess up inside. By the way I have read about Meades having the same problem - if left out in the Californian sun.

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My Meade's were "stored" in the Farm Shed back in Australia; it used to get up to 40+ in Summer and this is the first I've heard of melting/ dripping grease!

Must have been lucky, or something.....

( I'll run a check with the guys on IceinSpace, see if anyone has had similar problems)

Ken

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Just to round of this thread I now think that it's the cold that caused the lubricant to separate and some of it drip. After reading all the advice I could find I took the corrector plate off (surprisingly easily) Cleaned the inside surface and secondary mirror with Baader Wonder Optical fluid and optical quality tissues. It all went back perfectly and to my utter amazement the collimation was spot on. It looks like new now and last night had some stunning views of Mars, the Moon and Saturn.

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