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I own an 8” Celestron that was manufactured circa 1985 and I have owned it for the last 30 years. During this time I  have never cleaned the mirror, being too scared to do so. It has been bothering me lately so I looked on YouTube and saw a guy demonstrating how to do it with a very similar looking 8” Celestron. It involved no more than unscrewing 6 small screws that held the retaining ring for the top corrector plate and lifting it out. This exposed the main mirror which I could easily reach down to and clean as shown on YouTube, as well as the secondary mirror and corrector plate of course. The mirror had not looked dirty, but the difference after  cleaning was remarkable, it sparkled! I can’t wait for the dark nights to return and revisit a couple of galaxies I photographed last year and take them again to see the difference, hopefully there will be an improvement. I will of course need to do some collimating first!

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Sounds like you got a good result with the cleaning process. Hope you get some good opportunities to revisit some earlier targets for comparison. It would be good to read about, or even see comparativ

Excellent stuff. Of course cleaning mirrors will go part way to restoring performance. Reading this thread and some on other forums recently having returned to the hobby after a 25+ year absence, I kn

That's exactly what we want to avoid, and I would encourage you to carry on posting your thoughts. I agree some things can be more emotive than they perhaps should be, and as mods we do try to keep a

I assume you put the corrector plate back in exactly the same position, for that is very critical for good performance. You say: 'the mirror did not look dirty' so why taking the risk of cleaning it?? Cleaning the mirror of an SCT while still in the tube is not a good idea either...

Waiting for dark nights is not needed, Jupiter is very prominent in the night sky and a great target for an SCT. 

I hope the sparkling is not caused by little scratches you made when cleaning...
Did you use the opportunity to flock the tube as well?

Good luck to you

Edited by Waldemar
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Yes, I did replace the corrector plate in the exact same position, the importance of this was stated in the video. The reason I cleaned the mirror was because although it didn’t look dirty as such I could see some spots on it and reasoned that after 35 years it probably needed it, I wasn’t wrong because there was a noticeable difference in the before and after look of it. No, the sparkle is not due to scratches, just a bright clean shine, my goodness, do you think I used emery paper?

The reason for looking forward to the dark nights was, as stated, to re-photograph a couple of galaxies to see if they look any better, I am of course well aware that there are currently objects in the night sky to observe.

I have to say I do not like the condescending tone of your post, you come across as a highly critical know-it-all, tone it down a tad. Good luck to you too.

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Sorry, if I sounded a bit harsh, did not mean to. I love those old SCT's and to me it sounded as if you took a huge risc.
The way you wrote about it made me think you did this just for doing it, not because it was really neccessary...
To me that is not a smart thing to do.
Normally mirrors don't sparkle, they just reflect. If they sparkle that means the reflecting light is scattered by scratches. I hope that is not the case with yours. You do not need emery paper to ruin a mirror. Those old SCT's did not have a protecting layer, yet and are ruined by just softly whiping them with a cotton ball. The only way to clean them the right way is to dismantle the mirror, so it can be flushed with distilled water. But you will know soon enough I guess...

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I don’t understand why you are taking my use of the word “sparkle” so very literally, it was just a throw away remark to describe how clean the mirror is. The mirror has not the slightest single scratch on it, that I can guarantee. I have owned a telescope of one sort or another for the last 58 years and I am therefore fully aware that even cotton wall can scratch a mirror. I first used a hand squeeze air puffer to gently blow away any objects on the surface that could cause scratches. Then using water with a weak mix of washing up liquid I gently dabbed the mirror with cotton wool. After that I dabbed it dry. Then I dabbed it with distilled water until all the soap was gone and then dabbed it dry. I repeated it with distilled water again to make sure all traces had gone and then again dabbed it dry. The finished article looks great, it doesn’t actually sparkle, caused by scattered reflected photons, it’s just that clean. I hope that’s finally put that to bed. I appreciate that removing the mirror and thus being able to give it a good flush with distilled water would be the ideal way of doing it. However, not everyone has the ability or skill to take on such a high risk endeavour and in my case at the age of 73 and with a damaged spine, courtesy of advanced prostate cancer, it is beyond my physical abilities which is why I made do with cleaning it in situ, it did the job. I appreciate that you are unaware of my physical disabilities but even fit and healthy people may baulk at removing the mirror and you seem to assume it’s something we could all do. Not so.

I wish I had never bothered with this post, I deliberately put it in the Getting Started section as an encouragement to beginners who may, like me, have started out with a second hand ‘scope. I did not expect my remarks to be criticised by an experienced observer who owns a number of ‘scopes and who must think I am dumb. 

Anyway, I will leave it there, I have no interest in pursuing this conversation.

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Sounds like you got a good result with the cleaning process. Hope you get some good opportunities to revisit some earlier targets for comparison. It would be good to read about, or even see comparative images.

Dark Skies.

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Yes, I am delighted with the results, the mirror looks so clean now, not really surprising after 35 years without a clean.  Last year was my first full year of astrophotography using a digital camera, previously I used film. I received a great deal of help here on how to do it, otherwise I would have really struggled, people have been so helpful. I am looking forward to seeing if a clean mirror will result in a visible improvement in my images, in particular I will compare with last January’s images of M51 Whirlpool Galaxy and M81 Bode’s Galaxy using the exact same exposure times and number. I will be happy to post up the results.

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Echo the comments of others here

A little bit of dust on primary mirror, will not distract from viewing or imaging

Would not have touched it

Had a club Dob a while ago, club member was caring for

When he returned it, as was no longer able to care for it, I finished up with it

When opened the box, the box was full of cockroaches and spiders

Apparently he had it stored in back garden shed

When inspected the tube, found was full of spider webs, and primary mirror covered in cockroach much

I removed the primary, and soaked in distilled water for about an hour

Then using mild detergent, rubbed my fingers over the primary

Rinsed with distilled water, and re-assembled

This was an exception to the rule, with respect to cleaning primary mirrors

Had my collapsible Dob now over 10 years, and out couple times per month doing presentations in primary schools/scout groups

Have never had need to clean primary

John

 

PS

Early next year, NASA is sending another Rover to Mars

The attached link, will enable you to register and have your name included on the Rover, and can also download a Boarding Pass

https://mars.nasa.gov/news/8440/nasa-invites-public-to-submit-names-to-fly-aboard-next-mars-rover/

  

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Glad to hear that after 10 years you have not needed to clean your Dob’s primary mirror. 

When it comes to mirror cleaning I personally don’t consider it necessary to wait until an astronomical telescope’s mirror is covered in cobwebs and cockroach muck before cleaning it, a little surface coating of grime and dust is enough to get me cleaning, call me fussy. Let me know how you feel about cleaning your Dob’s mirror after another 25 years, on second thoughts, don’t bother, I will long gone by then and beyond caring.

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I cannot speak with any previous experience that would prove that cleaning the primary mirror would result in any improvement, it’s just my belief. When I saw the exposed mirror for the first time, that had never been cleaned in 35 years, it appeared to have a rather dull finish to it, so I cleaned it. After cleaning it looked a lot better, cleaner, brighter, and because it looked brighter that would suggest to me at least that it was reflecting more light than previously, which has to be a good thing.

We are always told how “every photon counts” and we work really hard, especially in astrophotography, to collect every single photon we possibly can. The only piece of equipment that collects and focuses those photons, is the primary mirror,  the secondary mirror of course can only work with the photons it is given. It just makes perfect sense to me that the condition of the primary mirror must be crucial to the end result and must therefore be looked after. It makes little sense to me if the mirror is manufactured to a degree of accuracy of say 0.57 arc seconds resolution but is covered in grime, but then again maybe that’s just me being stupid.

It was never my intention to start an argument about the pros of cons of mirror cleaning, I was merely trying to be helpful but instead have been shouted down. So be it, but nothing will ever change my mind that it is beneficial to clean a dirty mirror, you wouldn’t use a dirty eyepiece, so why use a dirty mirror?

There are tons of videos on YouTube showing how to clean a primary mirror, but I guess all those guys that think it’s a good idea must be wrong. There is also a video showing the cleaning of the 200” mirror at Mt. Palomar, they must all be wrong as well.  I however remain convinced that a clean mirror is even more important than a clean eyepiece. I have said my piece, I will leave it for others to make up their own minds. Good luck.

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Just a brief update. Had a clear night so took the opportunity to collimate my ‘scope, as it happens it took very little adjustment, much to my surprise. The stars are pin sharp and bright, perfect images, and I am very pleased with the result. Now it’s done and turned out to be so easy to do I wish I had done it years ago, but at least it’s done now. 

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Excellent stuff. Of course cleaning mirrors will go part way to restoring performance. Reading this thread and some on other forums recently having returned to the hobby after a 25+ year absence, I know I am right to keep quiet about how I maintain and use my astronomy eqipment, as there are always those all too ready to treat people as idiots, as they always know best. 

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2 minutes ago, RobC62 said:

Excellent stuff. Of course cleaning mirrors will go part way to restoring performance. Reading this thread and some on other forums recently having returned to the hobby after a 25+ year absence, I know I am right to keep quiet about how I maintain and use my astronomy eqipment, as there are always those all too ready to treat people as idiots, as they always know best. 

Hello and welcome to SGL

The point of this forum is to share experience I believe so that those new to the hobby can get up and running and enjoying themselves and also so that older hands can pick up new ways of doing things as well :smiley:

There is an immense amount of experience collectively within the forum membership and in my 10 years here I've noticed that people are certainly not treated as idiots.

 

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On 21/06/2019 at 13:10, Moonshed said:

It was never my intention to start an argument ...

Naw, I think that’s obvious to everyone. You were ambushed . 😑

Glad the exercise worked out well for you, Moonshed. And, anyhow, faffing with a scope is always satisfying ... 😊

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1 hour ago, Floater said:

Naw, I think that’s obvious to everyone. You were ambushed . 😑

Glad the exercise worked out well for you, Moonshed. And, anyhow, faffing with a scope is always satisfying ... 😊

Thanks for that. I agree that faffing about with the gear is part of the enjoyment. My brother-in-law for example  is a keen angler and spends way more time in his shed messing about with his gear than he does fishing, a bit like me and my telescope. 😊

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1 hour ago, RobC62 said:

Excellent stuff. Of course cleaning mirrors will go part way to restoring performance. Reading this thread and some on other forums recently having returned to the hobby after a 25+ year absence, I know I am right to keep quiet about how I maintain and use my astronomy eqipment, as there are always those all too ready to treat people as idiots, as they always know best. 

Yes, I am very glad I have cleaned it, I am sure it will go a long way to improving my images. Glad to see you have returned to the fold. Things have changed a lot since I started all those years ago, the mounts have become very accurate and the GOTO function saves a lot of time and trouble. The computer software for on screen viewing and controlling has come on in leaps and bounds, as has imaging editing programmes such as Photoshop. The one thing that has not changed much is the ‘scope itself, although the advertisers make impressive claims about mirror accuracy and resolution. 

It’s a great hobby, the only one that has stayed with me since I was a kid.  Sky At Night did a special offer, it must have been around 1960, in conjunction with Charles Frank of Glasgow for a very cheap 4” reflector with a table top mount. The mirror was held in place by what was in effect a bicycle clip. I will never forget my first look at the Milky Way, I was blown away! That amazement at the beauty of the universe has never left me, what better hobby is there?

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2 hours ago, Waldemar said:

I am very glad everything worked out well for you and my worries were unfounded. Congrats!

Thank you. It’s amazing I actually managed it!

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Glad the cleaning of optics worked out. I think the points being made above are simply because if a scopes optics look dirty to you, it may not need cleaning. A small amount of dirt on the optics wont give any less performance.

 

 

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1 hour ago, LukeSkywatcher said:

Glad the cleaning of optics worked out. I think the points being made above are simply because if a scopes optics look dirty to you, it may not need cleaning. A small amount of dirt on the optics wont give any less performance.

 

 

That all depends on what you would describe as “a small amount of dirt”. The mirror looked to me as though it needed cleaning so I cleaned it. What’s the problem? The worst that could happen is that cleaning it makes no discernible improvement, but on the other hand it could result in definite improvement. When I saw them cleaning the 200”at Mt. Palomar on YouTube I decided that if they think it’s a good idea then that’s good enough for me. I am delighted with the result. Those that don’t like the idea of cleaning their mirror don’t have to, their choice.

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On 21/06/2019 at 13:10, Moonshed said:

It was never my intention to start an argument about the pros of cons of mirror cleaning, I was merely trying to be helpful but instead have been shouted down.

Glad to hear your C8 is performing nicely.  I'm of the opinion that a film of fine dust on the mirror surface accumulated over years wouldn't affect the sharpness or contrast of the views, but may well reduce the light throughput of the mirror, resulting in a sightly dimmer image. The before and after difference you describe certainly indicates to me that the cleaning was worth doing.

One point I'd make is the international nature of the forum, and that it can be easy to miss-read the tone of the posts from members who's first language isn't English, as indeed it can be for any body of text written by someone not well known to us.

 

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20 minutes ago, CraigT82 said:

Glad to hear your C8 is performing nicely.  I'm of the opinion that a film of fine dust on the mirror surface accumulated over years wouldn't affect the sharpness or contrast of the views, but may well reduce the light throughput of the mirror, resulting in a sightly dimmer image. The before and after difference you describe certainly indicates to me that the cleaning was worth doing.

One point I'd make is the international nature of the forum, and that it can be easy to miss-read the tone of the posts from members who's first language isn't English, as indeed it can be for any body of text written by someone not well known to us.

 

Yes, you make a good point about it being easy to miss-read the tone of the posts when English isn’t the first language. I just felt that by cleaning the mirror I had nothing to lose apart from wasting a little time.

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21 hours ago, Moonshed said:

Yes, I am very glad I have cleaned it, I am sure it will go a long way to improving my images. Glad to see you have returned to the fold. Things have changed a lot since I started all those years ago, the mounts have become very accurate and the GOTO function saves a lot of time and trouble. The computer software for on screen viewing and controlling has come on in leaps and bounds, as has imaging editing programmes such as Photoshop. The one thing that has not changed much is the ‘scope itself, although the advertisers make impressive claims about mirror accuracy and resolution. 

It’s a great hobby, the only one that has stayed with me since I was a kid.  Sky At Night did a special offer, it must have been around 1960, in conjunction with Charles Frank of Glasgow for a very cheap 4” reflector with a table top mount. The mirror was held in place by what was in effect a bicycle clip. I will never forget my first look at the Milky Way, I was blown away! That amazement at the beauty of the universe has never left me, what better hobby is there?

Astronomy for me comes a VERY close second to my rc helicopters. Skill levels in both have to be learnt and honed, but astronomy does not tend to result in equipment ending up in twisted heaps in a field when gravity wins! Haha!

I have to agree with you on how the hobby - well science to be fair - has come on in leaps and bounds since my previous foray when all I started with was a book by J Texeraux, a 14" pyrex blank and a whole plethora of grinding materials as a first attempt at making a mirror. 8 months or so down the road of abject monotony of hogging, grinding, polishing ad infinitum and it was done. And, according to the test reports, remarkably so!

The rest was easy to fabricate with access to a machine shop and soon I had myself a quite good driven equatorial newtonian.

This time round is a wholly different episode, with pretty much everything bought in (could not help motorising the focusser and filter wheel with steppers and home brewed circuitry though! Old habits!) and I have myself a low-end 8" nice Skywatcher EQ5 GOTO second hand, but nowhere near as powerful scope for not a lot of money (not saying how much, but it was VERY cheap, but the tube had been left open during a house renovation and the mirrors were needing a c... l...e...a...n. lol!!!)

I am sure it can be improved, but as it is, it is remarkable how it can all done for the prices, plus it is a useful tool for use doing my late-in-life physics/astronomy degree. And my batch two children positively jump for joy when the get to see the moon and jupiter etc.

Great fun and very educational.

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You made your own 14”? Wow, that’s impressive! I am pretty sure I could grind a blank, maybe, sort of, perhaps, but that’s as far as I would get, no mechanical construction  skills I’m afraid and my electrics run to changing a plug. When I was young my brother and I would think nothing of lifting out a car engine in the street and putting in new big ends, or replacing a broken synchromesh gear in the gearbox, but fixing things is very different to making things. Flying rc helicopters sounds difficult but fun, I used to watch the local club fly their planes near where I used to live in Scotland, but it wasn’t for me, I took up gliding instead and absolutely loved it. Flying gliders was the one hobby I loved as much as astronomy until ill health unfortunately put a stop to it. Enough reminiscing, waiting for another clear night to use my super clean mirror! Of course since I cleaned and collimated it there has been constant cloud cover, such is life.

Well done on taking on a physics/astronomy degree, bet it’s fascinating stuff you are learning. Good luck with that.

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