Mirror cleaning

[ollypenrice]

My own view is that we should concentrate on looking through optics and not at them.  They rarely, if ever, look perfect when we scrutinize them but it's surprising how dirty they have to be for a perceptible degradation to occur when we use them. Since this thread will be read by people in the future I think it's worth saying that the consensus in the community is to resist the temptation to clean mirrors which are not pretty dirty. In the case of refractors, however, there is a case for removing pollen which can attack anti-reflective coatings if left in place. 

My point here is a general one and not directed specifically at the OP.

Olly

[Moonshed]

1 hour ago, ollypenrice said:

My own view is that we should concentrate on looking through optics and not at them.  They rarely, if ever, look perfect when we scrutinize them but it's surprising how dirty they have to be for a perceptible degradation to occur when we use them. Since this thread will be read by people in the future I think it's worth saying that the consensus in the community is to resist the temptation to clean mirrors which are not pretty dirty. In the case of refractors, however, there is a case for removing pollen which can attack anti-reflective coatings if left in place. 

My point here is a general one and not directed specifically at the OP.

Olly

I think it has been made abundantly clear on this thread that some people don't agree with cleaning a mirror that looks dirty. Okay, got it! Honest! However, it just so happens that it is my personal view that my mirror was dirty enough to need cleaning so I cleaned it. I take the view, which I have already repeated, that if it didn’t need cleaning then so what, no harm done, just a little time spent on maintenance that perhaps wasn’t necessary. I, unfortunately, do not posses the skills necessary to be able to eyeball a mirror and tell if the grime needs removing or not, so take the view that if in doubt then clean it. Okay, others disagree and feel it best to leave it as it is. That to me though, to be honest, is just bizarre and illogical, because by cleaning a mirror it will either improve it or make no difference and as I lack the skills to tell which, then I will clean it as it’s everything to gain and nothing to lose. Maybe you could define what you mean by “pretty dirty” because that is just a subjective assessment and not a scientific reading of an instrument. Perhaps someone instead of saying it isn’t necessary to clean a dirty mirror will be good enough to explain to me how on earth you can tell, just by looking at a dirty mirror, if it needs a clean or not, because I have no idea on how to do that, which is why I cleaned it. Many thanks in advance.

ps I take it that when you referred to cleaning refractors you were referring to cleaning the lenses as of course they don’t have mirrors. Or perhaps it was a typo and you meant to say reflectors? Just saying for clarification as this thread will read by people in the future.

Edited June 25, 2019 by Moonshed
Typo

[Stu]

@Moonshed I'm sure Olly was referring to refractors, and I would agree that cleaning them every now and then to remove deposits which might damage the coatings is worthwhile. It can also reduce light scatter around planets and bright stars, helping the views look 'tighter'. I have done my Tak a couple of times, and am always meticulous about making sure there is no grit present which might scratch the coatings.

I think the points being made against cleaning a mirror relate to the possibility of causing damage if done incorrectly. You mention that the worst case is just some wasted time and a view that looks the same, actually the worst case is a scratched mirror or optics and poorer performance, so these things always need to be done with care. It is not unheard of for people to damage mirrors with their first surface coatings and wishing they had just left things untouched. I know you probably know this, I'm just pointing it out for complete clarity.

I'm sorry you have felt under attack. I really don't think that was the intention and hope you don't feel dissuaded from posting on similar subjects in future. I can only encourage people to use emoticons to convey tone where appropriate. I hate the things myself, but they are very useful for avoiding misunderstandings. It's harder to react badly if there is a smiley at the end of the sentence 😀😀👍👍

[Moonshed]

38 minutes ago, Stu said:

@Moonshed I'm sure Olly was referring to refractors, and I would agree that cleaning them every now and then to remove deposits which might damage the coatings is worthwhile. It can also reduce light scatter around planets and bright stars, helping the views look 'tighter'. I have done my Tak a couple of times, and am always meticulous about making sure there is no grit present which might scratch the coatings.

I think the points being made against cleaning a mirror relate to the possibility of causing damage if done incorrectly. You mention that the worst case is just some wasted time and a view that looks the same, actually the worst case is a scratched mirror or optics and poorer performance, so these things always need to be done with care. It is not unheard of for people to damage mirrors with their first surface coatings and wishing they had just left things untouched. I know you probably know this, I'm just pointing it out for complete clarity.

I'm sorry you have felt under attack. I really don't think that was the intention and hope you don't feel dissuaded from posting on similar subjects in future. I can only encourage people to use emoticons to convey tone where appropriate. I hate the things myself, but they are very useful for avoiding misunderstandings. It's harder to react badly if there is a smiley at the end of the sentence 😀😀👍👍

I think it is obvious that before tackling cleaning a mirror for the first time that a lot of research would be done first. As I pointed out there are no end of videos on YouTube showing exactly how the job should be done and I watched quite a few of them before cleaning the mirror. I did not go into it blind, I knew exactly what I was doing so there was no chance of me scratching the mirror or in any way causing damage. Looking at the comments posted by those that say I should leave a dirty mirror alone in case I scratch it or whatever, it does  give a very strong impression that they must think me daft because that is exactly how it comes across. You may think otherwise but I am not alone in thinking this, that’s all I am saying.

I have grown tired of this, it is endless, every time I say things could only get better not worse after cleaning the mirror, without exception along comes someone who says to leave it alone because it could get scratched. I give up, there was not the slightest risk of me scratching it, I have been observing since 1960 and have a pretty sound knowledge of looking after and cleaning lenses and a reflector mirror that was easy to remove. I have no wish to explain yet again why I cleaned the mirror so will not bother to respond to those that say I should have left it dirty, even though the outcome is very positive. I hope nobody takes offence, none meant 👍😀😍😆😇

[kirkster501]

Here is an article on my website about cleaning mirrors.

https://www.sjkastro.com/cleaning-12-dobsonian-mirror/

The website is very much under development.

[Stu]

@Moonshed I was simply explaining why you got the reaction you did. There are many new starters on this forum, so the general advice to be cautious and leave well alone unless absolutely necessary is valid. I was not making any assumptions about your knowledge or capabilities, simply explaining the context to you.

I was trying to help, but clearly even my smileys failed in this case 😥😥

[Moonshed]

3 hours ago, Stu said:

@Moonshed I was simply explaining why you got the reaction you did. There are many new starters on this forum, so the general advice to be cautious and leave well alone unless absolutely necessary is valid. I was not making any assumptions about your knowledge or capabilities, simply explaining the context to you.

I was trying to help, but clearly even my smileys failed in this case 😥😥

No Stu, you have not definitely not failed you have helped, I understand exactly where you are coming from and understand the points you are making, with or without smileys 👍. Perhaps in future posts, should the subject rear its ugly head again, (Oh No the Moderator cries!!!) those against mirror cleaning should simply clarify that if not done correctly damage could be done to the mirror (which to be honest I would have thought to be blindingly obvious) so before starting out just be sure they have thoroughly researched how it should be done properly to avoid any possibility of scratching, and that being done then go ahead and clean the mirror if it looks dirty. On the other hand it may not be necessary as some dirt apparently makes very little difference, so if you are  not confident in your ability to do no damage then leave it alone. I think that neatly sums up all the anti-cleaning brigade points so as not to mislead any beginners. Are we all happy with that?

Funny isn’t it? I started this thread solely for the benefit of virgin mirror cleaners, who, like me, are afraid to clean the mirror. My first “serious” ‘scope is the 8” SCT I currently own and I bought it second hand as I could not afford a new one back then and I felt that surely today there must be others in the same financial boat I was in. It can be very difficult to justify spending say £1500 on a brand new ‘scope and mount etc. when there is a mortgage and bills to pay and kids to raise, Oh, yes, I remember it well. Buying a used ‘scope makes a lot of sense when on a tight budget, as most of us are? But sometimes they may need a little TLC, and dare I say it, some mirror cleaning may be necessary. I eventually found that cleaning the mirror in situ to be such a simple thing to do that I just wanted to let others, principally beginners, appreciate that it was in fact very easy and straightforward to do and not to be afraid of doing it.

That was my intention in its entirety, to help others, nothing more, I meant well. I had no idea the hornet’s nest it would stir up with so many members being so critical of my every comment, I would never have thought it. Had I known in advance the reaction my “helpful” post would create I would never  have said a single word, it’s just not worth it. Next time I want to be helpful  I will resist the temptation and think back on what happened here and think again.

[Stu]

1 minute ago, Moonshed said:

Next time I want to be helpful  I will resist the temptation and think back on what happened here and think again.

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 lid on things although there is nothing wrong with a good natured exchange of views. We are all different and have different sensitivities. There was nothing wrong with what you did, and hopefully everything will calm down now

There are some that think keeping a mirror clean actually does have a noticeable impact on the views and I do tend to agree with that, so we shouldn't be scared to clean them, so long as it is done careful.

Please don't let this put you off!

[Moonshed]

4 hours ago, kirkster501 said:

Here is an article on my website about cleaning mirrors.

https://www.sjkastro.com/cleaning-12-dobsonian-mirror/

The website is very much under development.

I had a look at your website and have to say the advice you give is both good and clear, easy to follow. Well done on a good job, I am sure it will be a great help to many first timers on how to properly clean their primary mirror. Well done.

[John]

I tend to clean the primary mirror of my 12 inch dobsonian about once per 12-18 months. It's not a difficult task and there is some excellent guidance available on the correct way to do it without damaging the mirror coatings. I tend for follow this advice from R F Royce:

http://www.rfroyce.com/cleanfsm.htm

My primary was last coated by Orion Optics about 9 years ago and the coatings are still in good shape. The reflectivity will have decreased a little year by year of course but the scope still seems to perform really well when the clouds and seeing permit.

I believe that over-cleaning can ultimately cause deterioration in the mirror coatings through repeated immersion in water and there is also a risk of accidently allowing an abrasive particle to be on the mirror during the cleaning process which will create micro scratches which in turn will produce unwanted diffraction reducing sharpness. Neither of these issues mean that the mirror should not be cleaned but perhaps lead towards cleaning with care and when really required ie: when the build up of dust and debris is enough to have a noticeably detrimental impact on performance.

The other guidance with mirrors is that they look awful when you shine a torch or fire a camera flash at them - even when they are actually clean and in great condition

It's all just common sense, isnt it

 

[Moonshed]

1 hour ago, Stu said:

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 lid on things although there is nothing wrong with a good natured exchange of views. We are all different and have different sensitivities. There was nothing wrong with what you did, and hopefully everything will calm down now

There are some that think keeping a mirror clean actually does have a noticeable impact on the views and I do tend to agree with that, so we shouldn't be scared to clean them, so long as it is done careful.

Please don't let this put you off!

Stu, you are right! I should not be put off from posting my thoughts just because a very small minority are know-it-all highly critical people who love to put people down. You may find this hard to believe, but then maybe not, but one of that group, who has posted here, first responded to a post of mine about two years ago when I was starting out in digital astrophotography for the first time, previously having used a film camera. There was so much to learn, people talking about flats, darks, lights, bias, exposure times and number of frames, stacking, and not to mention the complexities of Photoshop. People were so helpful and gave me so much help and advice, except one or two that is. One in particular said that with my set-up I should forget all about imaging deep sky objects and instead content myself with the moon and solar system! When I eventually produced a nice image of the Orion Nebula many members said it was a good first start and to carry on and get more practice and gave me some good tips, his only comment was to say the image was awful, all nebula. Not once has he given me helpful and constructive criticism, just put downs. Can you believe that? Why do people do that? If they cannot find something good to say or offer helpful advice then they should not say anything! He hasn’t changed one iota. It seems to me it doesn’t matter where you go you will always find a small minority of people like that, I usually just ignore them because the vast majority of people, here and elsewhere, are nice, decent, helpful people who genuinely want to help you succeed in your new venture.

For that reason I will not be put off by the few nasty critics here but will continue to post in my usual way. Thanks for the good advice, much appreciated!

[Moonshed]

48 minutes ago, John said:

I tend to clean the primary mirror of my 12 inch dobsonian about once per 12-18 months. It's not a difficult task and there is some excellent guidance available on the correct way to do it without damaging the mirror coatings. I tend for follow this advice from R F Royce:

http://www.rfroyce.com/cleanfsm.htm

My primary was last coated by Orion Optics about 9 years ago and the coatings are still in good shape. The reflectivity will have decreased a little year by year of course but the scope still seems to perform really well when the clouds and seeing permit.

I believe that over-cleaning can ultimately cause deterioration in the mirror coatings through repeated immersion in water and there is also a risk of accidently allowing an abrasive particle to be on the mirror during the cleaning process which will create micro scratches which in turn will produce unwanted diffraction reducing sharpness. Neither of these issues mean that the mirror should not be cleaned but perhaps lead towards cleaning with care and when really required ie: when the build up of dust and debris is enough to have a noticeably detrimental impact on performance.

The other guidance with mirrors is that they look awful when you shine a torch or fire a camera flash at them - even when they are actually clean and in great condition

It's all just common sense, isnt it

 

Good advice, and the website on cleaning mirrors is also good. I think you have summed it up nicely with your remark that it’s all just common sense, because when you get down to it, it is!

[dyfiastro]

I think common sense is the main thing here along with a good dose of patience and research.
Both my Newts have been cleaned on a number of occasions but there was a reasoning behind it. the 130p got cleaned every spring before being put away for the summer and likewise the 200p got cleaning before being put away for the winter.

Living about 100 yards from the beach the amount of sand and salt that accumulates over a season for me is more than enough reason to clean on a regular basis.
For me it is very much a lesser of two evils, take the small chance of damaging the mirror whilst cleaning or the much larger chance of damaging the mirror over time due to salt and sand deposits.

Having just aquired an old SCT and stripping that down as well for reasons that again made sense.
The SCT in my case had a small amount of fungus growing on the inside of the corrector plate and had been stored for a few years. Treating the fungus was the main goal and cleaning was a part of that.

If I lived further in land and my gear was not subjected to such issues I would not be cleaning anywhere near as often, however I do feel that its something that I would still do once every few years and something that is just part of owning a scope (and no different really to cleaning a camera lens and sensor).

[Moonshed]

7 hours ago, dyfiastro said:

I think common sense is the main thing here along with a good dose of patience and research.
Both my Newts have been cleaned on a number of occasions but there was a reasoning behind it. the 130p got cleaned every spring before being put away for the summer and likewise the 200p got cleaning before being put away for the winter.

Living about 100 yards from the beach the amount of sand and salt that accumulates over a season for me is more than enough reason to clean on a regular basis.
For me it is very much a lesser of two evils, take the small chance of damaging the mirror whilst cleaning or the much larger chance of damaging the mirror over time due to salt and sand deposits.

Having just aquired an old SCT and stripping that down as well for reasons that again made sense.
The SCT in my case had a small amount of fungus growing on the inside of the corrector plate and had been stored for a few years. Treating the fungus was the main goal and cleaning was a part of that.

If I lived further in land and my gear was not subjected to such issues I would not be cleaning anywhere near as often, however I do feel that its something that I would still do once every few years and something that is just part of owning a scope (and no different really to cleaning a camera lens and sensor).

I agree with your thoughts on mirror cleaning and that common sense should prevail. I doubt if I will need to clean mine again, by the time it needs cleaning I will have probably be pushing up the daisies. Obviously the interval between cleans depends very much on individual circumstances and the situation you are in demands regular cleaning, whereas in my case, living about 5 miles from the coast, not so often. Having said that, leaving it for 35 years was clearly way too long and I really should have cleaned it years ago but was too cowardly, however, I am now a super hero and fear no mirror!🎖 It does make sense to me to keep it clean in the same way that we keep our lenses, eyepieces and cameras clean. Sometimes the condensation here around November time can be horrendous and after a night’s observing everything will be wet so in that situation my case of optical bits and bobs comes indoors instead of staying in the “Moonshed” ( so named by my granddaughter and been called that ever since, hence my sign-in name) and everything gets a good clean. Makes sense to me to keep everything clean.

[kirkster501]

12 hours ago, Moonshed said:

I had a look at your website and have to say the advice you give is both good and clear, easy to follow. Well done on a good job, I am sure it will be a great help to many first timers on how to properly clean their primary mirror. Well done.

Thankyou, kind of you to say.  It is very much in development and there are a few bugs but I am getting there.   A bit sparse on content still but I have a backlog of stuff to write up and post.

[Moonshed]

9 hours ago, kirkster501 said:

Thankyou, kind of you to say.  It is very much in development and there are a few bugs but I am getting there.   A bit sparse on content still but I have a backlog of stuff to write up and post.

Well, so far so good. Your photographs are amazing, I especially like your M31 image, great detail and colour.

[Geoff Barnes]

No point starting a new thread, I've just taken my 12 inch mirror off and given it a wash, after 14 months it had developed a slight opaque greyish film over it.

No problems at all with the cleaning, the mirror looks like new again.

My reason for posting is that when I got the mirror cell off I noticed that the 3 black mirror clips were all slightly loose and wobbly. They are all attached with 2 screws so I decided to tighten them just enough to stop the wobble without putting pressure on the mirror edge.

I'm wondering if this could be the reason why my mirror goes out of collimation every time I move the scope around?

Surely the clips are meant to grip the mirror so that it can't move?

Anyone else found their clips to be loose and did you tighten them?

[John]

Mirror clips are supposed to hold the primary in place without gripping it as I understand it. I read somewhere that there should be a gap the thickness of a playing / business card between the top surface of the mirror and the bottom surface of the clip.

Sometimes the springs fitted to the collimation screws are a little weak which can cause the scope to go out of collimation when moved around. I didn't think this was an issue with Skywatcher dobs though ?

 

[Geoff Barnes]

6 minutes ago, John said:

Sometimes the springs fitted to the collimation screws are a little weak which can cause the scope to go out of collimation when moved around. I didn't think this was an issue with Skywatcher dobs though ?

Funny you should mention that John, because the scope was going out of collimation so much I recently changed the original SW springs for much stronger ones to see if that solved the problem. I haven't had much chance to use the scope for a few weeks with the rotten winter weather here, but it will be interesting to see if my efforts prove fruitful when the skies clear.

[dyfiastro]

Its also worth checking how well the mirror fits into the primary holder. One of mine had a fair amount of movement which seemed to allow the mirror to move side to side etc...
I added a thee extra bits of sticky back foam around the inside of the holder to take up some of the slack, this has solved the issue with the mirror slopping around in its holder.