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200P Mirror - Am I stuck with the stuck bit?


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My dew cap, made from a camping bag foam base with its interior painted with black emulsion from a sample pot, works quite  well for me. However a very small piece of foam is now on the primary 200P mirror and bouts of  condensation appears to be keeping it there.

I have read that under no circumstances should a novice like myself touch the mirror to remove it.

So, am I 'stuck' with it?

Any advice gratefully received.

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I would not have thought it is stuck too firmly ? try a hair dryer blowing up the tube and see if it will dislodge. A very small piece will not affect the view. I think I would be more concerned about any paint on the foam affecting the mirror coatings.     

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No, Have you tried leaving the scope with the open end of the tube pointing down - after an observing session? At worst remove the primary and carefully pick it off, don't worry if it leaves a slight blemish on the mirror as this will not affect the views you get in the slightest.

Ian

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No, Have you tried leaving the scope with the open end of the tube pointing down - after an observing session? At worst remove the primary and carefully pick it off, don't worry if it leaves a slight blemish on the mirror as this will not affect the views you get in the slightest.

Ian

Yeah, I was going to suggest whipping the primary out and just taking the foam off.

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The piece of foam won't affect the view.

But if it's bothering you, maybe hold the tube pointing at the ground with the dustcap off, then slap the tube next to the primary mirror will shift it.....perhaps.

Regards, Ed.

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Hi Scopey, If your anything like me it would do my head in!!!  Another thing you could try is just get a little distilled water and with a pupette or dropper, try soaking the little piece of foam with the distilled water - this would make the foam a lot heavier, tilt the tube downwards and then give the tube a little tap near to the offending little blighter - it may then just drop off following the laws of gravity - and not an apple in sight!!!!  hope you get it sorted mate.    Paul.

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Crikey, there's some good advise stuff going down here! Thanks again all you persons (watch out for sexism accusations).

Removing the primary mirror seems easy enough but I understand that after replacing it I probably will need to collimate it in order to maintain its 'sweet spot.' Now this all sounds a bit painful to me so, at present, I must proceed at a pace suitable to my current  demeanour  - ie lazy to almost full stop. After that, if the mirror needs removing then so be it. The 'sweet spot' must be maintained at all costs.  :smiley:

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Removing the primary is easy enough - not sure how many screws hold the mirror cell in place, before dismantling just mark the outside of the tube by the mirror cell with a little tape, then mark the back of the mirror cell continuing the tape "line" back across the mirror cell, so you can just line the tape marks up when placing the mirror back in - you don't even have to loosen or remove the mirror from its cell, just place on the floor near the tube, remove the foam, then return the mirror cell back into its place checking the tape is lined up - remember though - if you take the mirror cell out of the tube, make sure the tube is well supported as removing the mirror cell will alter the balance of the tube - if not supported the tube will be a lot heavier the focusser end.   Paul

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Just this Week I used one of those cans of compressed air, the ones used for cleaning out PC's ( which is what I was actually doing) Well, I had one arm down the end of the tube with the air can, whilst holding the Dyson hose over the focuser. I was surprised to how much dust was removed during this operation!

I've done what Northern Soul man has suggested, remove the outer screws of the whole mirror cell from the base of the OTA. Lots of gentle handling is essential., lay the OTA on a table  and sit on a chair to disassemble. Even use some cushions if need be!. Once cleaned, replace, and you shouldn't have to collimate?

I did this just to see how easy it was, prior to some future Modifications? The scope was good to go for the next viewing session.

Edited by Charic
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The first time I took the cell out it was very tight in the tube and I had to resort to a copper drift and gentle taps with a hammer. When I reassembled I smeared some copper grease round the rim, and subsequent removals have been that much easier. Replacing it takes patience. It's a tight fit in a flexible tube and the screw holes have to line up exactly. It can be frustrating but definitely doable.

Good luck!

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Following on from the above suggestions my observations on You Tube show that after removing the primary mirror cell I need to submerse this in tepid fresh water in a clean bowl adding 2 or 3 drops of a quality washing up detergent and leave to soak for about 5 minutes. Wash off with cold tap water. Repeat with tepid water and detergent  wiping cotton wool strips gently across the mirror. Rinse off with cold water allowing to drain on a clean towel. Finally pour distilled water over mirror and allow to drain and dry. And that's it.

Sounds straight forward enough - all I need is the confidence to do it, probably the year after next!

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Following on from the above suggestions my observations on You Tube show that after removing the primary mirror cell I need to submerse this in tepid fresh water in a clean bowl adding 2 or 3 drops of a quality washing up detergent and leave to soak for about 5 minutes. Wash off with cold tap water. Repeat with tepid water and detergent  wiping cotton wool strips gently across the mirror. Rinse off with cold water allowing to drain on a clean towel. Finally pour distilled water over mirror and allow to drain and dry. And that's it.

Sounds straight forward enough - all I need is the confidence to do it, probably the year after next!

NOT SO QUICK!   Only the Mirror should be dipped into water, which means dismantling from the mirror cell, If your just just removing a bit of foam, and there's no residue, just put the whole cell assembly back in the scope. But the temptation to clean it will be high?

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Never use tap water alone, it dries and leave behind all the salts and other minerals on the primary.

I have removed and cleaned mine, it's not that difficult. (This applies to my 200P).

So first off, I stuck a bit of tape on the OTA and then on the mirror cell outer casing making sure both bits of tape were aligned so that when I came to put it back together, the cell and OTA go back in the exact same spot (important).

I then undid the 3 or 4 screws that bolt the mirror cell to the OTA and gently lifted the OTA off the mirror cell (mine came of easy).

I then left the primary soaking in tepid water with a little blob of washing up liquid for 5 minutes or so (the washing up liquid was none of that fragranced stuff, just pure washing up liquid) and then using surgical cotton wool (yes there are different types of cotton wool) moving gently from the inside out, very gently wipe the primary. I changed the cotton wool after every wipe, just in case I picked and dirt and grit up, didn't want to scratch the primary.

Once done I propped it on its side (all the above had the mirror still in the cell) and poured IPA (Isopropyl Alcohol) over the mirror ,this will stop any streaks forming.

I then left to dry, then aligned the 2 bits of tape on the cell and the OTA up and inserted the cell and screwed back together, quick collimation and job done.

Took about 35 minutes.

Good luck.

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Depending on just how small it is, it would be easier to remove the primary - then just pick it off, very carefully with a pair of tweezers (if you have a steady hand). If there is anything left behind it is unlikely to degrade the image - mirrors can get seriously mucky before they need a clean.

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Well, I've absorbed the advice on here and pressed on!

I marked with tube with tape, to aid realignment later  when reassembling, and removed the primary mirror. There were two tiny deposits of foam with black emulsion from the dew cap. The mirror was submerged in a clean bowl of tepid tap water and 3 drops of  detergent and allowed to soak for 10 minutes. The deposits were a tad stubborn so, still submerged, I very gently prodded them with a plastic toothpick and away they floated. Next I removed the mirror and rinsed in cold tap water. Fresh tepid water and detergent was again added and the mirror submerged for a few minutes. Whilst still submerged I opted to very gently wipe cotton swaps across the mirror, a clean swab for every wipe. Next the mirror was removed and rinsed thoroughly with distilled water and put on a clean tea towel on the drainer to dry.

It looks good, in fact very good and I'm feeling quite pleased with myself at the moment. But I'm sure it won't last. I wonder what my challenge will be next?

Time for a well deserved tea and biscuits me thinks!

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I have to confess my initial reactions when reading this were thus:

"3 drops of  detergent" - Eeek, wince!

"I very gently prodded them with a plastic toothpick" - Eeek, wince!

"I opted to very gently wipe cotton swaps across the mirror" - Eeek, wince!

So has Daz been lucky or are the mirror coatings not as delicate as people say?

Edited by mitchelln
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........Most mirrors are `silvered` with Aluminium or Silver, which is the more expensive option. Silver offers better reflectivity.

Skywatcher telescopes receive an additional coating of Silicon Dioxide to help protect the mirrored surface. As long as your extremely carefull, there should be no reason why a dirty mirror shouldnt be cleaned by the user. I mean really dirty. a coating of dust wont hurt, but a spillage of coffee/cola would leave a terrible mess?
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Just this Week I used one of those cans of compressed air, the ones used for cleaning out PC's ( which is what I was actually doing) Well, I had one arm down the end of the tube with the air can, whilst holding the Dyson hose over the focuser.

Be careful using those cans of compressed air they contain propellants that can easily leave residual marks on a mirrors surface.
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Tepid water with a few drops of washing up liquid is the prefered method for cleaning valuable antiques so its what i allways used in my "scope with mirrors" days a lot of deposits are airborn grease etc so a solvent has to be used.

Alan

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Be careful using those cans of compressed air they contain propellants that can easily leave residual marks on a mirrors surface.

They will also spit out liquid propellant if not held completely upright at all times. They also tend to drip if operated for more than a few seconds. Deserves another - Eeek, wince! ;)

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have you heard the story about................

-take mirror from scope (cell and all)

-place it on the lawn...

-take a hosepipe and spray....

maybe not the best of ideas...but..!!!!

mirrors are quite 'flexible'..meaning...even though you touch

the surface (not recommended) they will survive..

It's not like when you touch the mirror with your fingers it will fall apart like

dracula seeing daylight...

I took out my whole primary mirror cell...(SW 10" Flex)

cell and mirror..

and washed it under with warm water, cell and all...

some detergent and isopropyl alcohol...no problem..

in any case..

they can withstand quite a bit, presuming they are treated nicely..

Don't worry too much about cleaning your mirror...

just don't do it too often..

and yes..flush with demi-water afterwards...

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