To clean or not to clean?

[kerrylewis]

The wise words seem to say 'Don't' but my Dob's primary mirror has a fine film of dust on it (it's kept in a garage) which looks especially awful if there is also some dew about. With a flashlight it looks terrible - but then everyone says 'don't look at it with a flashlight'. At what point is this going to affect the scope's performance?

Plus - I am planning to take it to SGLX and I could not stand the shame and ignominy if everyone said I had a filthy mirror! 

I know there are a few threads on this but I would be interested in some specific advice as to what point it is necessary to clean a primary. 

[Peter Drew]

There is no shame in having a dusty mirror, at SGLX, those "in the know" will think " there's a man that uses his telescope a lot and has the good sense to not be worried about its appearance" 

[Qualia]

Kerry, use a bulb blower to blow off any obvious debris, dead instects, pollen etc. It's probably the most sensible idea to leave it at that.

I've had my 10" for almost two years. In that time, it has had many sessions, travelled over 10,000 km and has been all over southern Europe. It has been out in all kinds of landscapes and weather: deserts, beaches, countryside, snow, dust storms, wind and gales, rain and scorching sun. Sure, the mirror was dirty, but the word 'dirty' is a relative term. A few months ago, I was thinking that I'd give the scope another 150 to 200 sessions, probably wait another 10,000 km and then see what happens.

That was until recently.

Over the last few weeks, I was beginning to see split diffraction spikes which was compromising my pleasure of Jupiter. I set up a thread for help and from the advice given, decided to remove the secondary and tweak the spider vanes. By the time I had done that, I figured it was a good moment to give the scope a general clean and a bit of tender loving care. Needless to say, I took out the primary and gave it a rinse and figured I could do the same with the secondary.

I think it is always worth losing fear. You know, taking apart the scope to understand its mechanics, to start from scratch with collimation, etc. But within that process, I honestly don't think it is necessary to clean the mirrors. Not unless you just want to see what happens. Then, it might be a useful empirical experiment.

In my own case, I can see that after cleaning the mirror - which was already purchased secondhand - will need resurfacing some time in the future. Something I have always been aware of ever since the scope was made for me. I can also say that both mirrors are now significantly brighter. The layer of muck has been soaked away but I cannot say whether this has actually improved on the mirror's sharpness, contrast or quality of image. My gut feeling says that it hasn't but of course, I will need a few more sessions to really arrive at a solid conclusion.

To actually clean the primary, I followed the directions in

link.

Hope this helps a little.

[ronin]

Really it is your choice, anything on my scopes drives me mad, to me optics should be clean. So I clean them.

Cleaning will make no noticable difference (unless really bad) in normal use, but maybe the GRS might just have been a bit more pronounced.

Avoid dishwashers and Karchers. :grin:

[Qualia]

Cleaning will make no noticable difference (unless really bad) in normal use, but maybe the GRS might just have been a bit more pronounced.

Curious you say that Ronin. Last night I was out viewing Jupiter and had the best session this season. Putting seeing to one side - for last night was no better than many other nights - I cannot decide if the quality of image was due to sorting out the spider vanes or giving the mirror a clean.

[Moonshane]

you can clean a mirror without even touching the surface so there is zero risk of damage. just soak it in warm slightly soapy water (literally a couple of drops) and swish around with fingers a close as you dare without touching. rinse with a shower spray and then with RO water or distilled water and allow to air dry - maybe blow off larger drops with a hairdryer.

the odd stubborn bit may stay on the mirror but this is unlikely to affect the views at all.

I have not washed my 16" mirror ever in the five years I have had it so send any complainers to me!

[kerrylewis]

Thanks for your input chaps. The SGLX comment was, of course, tongue in cheek!

I think I will leave well alone at least for the time being - especially as I have the manual dexterity of the average goldfish! I had some good views of Jupiter and then a few galaxies after the moon had set last night, so it can't be too bad.

I always leave the main plastic cover on the lower part of the tube, of course, but this is quite a distance from the mirror itself. I wondered about gently laying a lint-free cloth on the mirror itself when it is in the garage. Not a good idea?

[Moonshane]

Thanks for your input chaps. The SGLX comment was, of course, tongue in cheek!

I think I will leave well alone at least for the time being - especially as I have the manual dexterity of the average goldfish! I had some good views of Jupiter and then a few galaxies after the moon had set last night, so it can't be too bad.

I always leave the main plastic cover on the lower part of the tube, of course, but this is quite a distance from the mirror itself. I wondered about gently laying a lint-free cloth on the mirror itself when it is in the garage. Not a good idea?

not a good idea as it may attract and hold moisture - never good with a stored mirror.

[kerrylewis]

not a good idea as it may attract and hold moisture - never good with a stored mirror.

That's a very good point. I knew there must be a reason why it was not a good idea - it would have been suggested somewhere if it was.

One day, when I'm feeling brave, I will dismantle the scope and give a good valeting and MOT - but not today  

[Charic]

A covering of spilt Cola should affect your image, but a little dust is not a major problem. Mine always looks worse when viewed down the tube with a torch, but with this method of inspection, the mirror magnifies so it will always looks worse. By the time the Primary is removed, where has the dust gone?

But I'm with ronin here, I just remove and clean as often as I need too, as I have no collimation fears.

[niallk]

I keep thinking surely my 10" is dirty enough to warrant a cleaning - then I have a night out that shows better than ever detail... So to-date I've left it - shocking as it looks! I do think I'll do it for the learning experience though at some point maybe in the next year. Best of luck

[ghostdance]

I always leave the main plastic cover on the lower part of the tube, of course, but this is quite a distance from the mirror itself. I wondered about gently laying a lint-free cloth on the mirror itself when it is in the garage. Not a good idea?

Over winter I've been keeping my scope ( a comparatively small affair, takes up as much room as the average five year old, lol) indoors but with a shower cap over the primary end, with a little silica packet in the cap. I did start off keeping it in the garage but seemed to be too dusty and damp there, despite using the soft case.

I *think* the shower cap is insurance against major household whatnots, not sure about fine dust etc, but I try and avoid looking down the tube with a torch!

Saving mirror cleaning til I decide whether to flock, tbh

[swamp thing]

Best to look in the eyepiece mate rather than down at the mirror. 

Truss Dobs get filthy mate, don't worry about it. 

[Langworthy]

A fraught issue. Many of us seem to get paranoid about our kit, myself included!! I have a Sky-Watcher Explorer 200P. During these cold, cloud-free nights the primary mirror fogs up - and indeed the whole outside of the casing becomes wet - especially when I bring it indoors. Last night, back indoors, I noticed when I shone a light down the tube to see if the mirror was still fogged that it appeared speckled with what looked like dots/stains ... as if it had been splashed by something (I keep the cover on at all times when not in use). Naturally this morning the mirror is unfogged and in natural light seems spotless. But when I shine the torch on the surface once again the dots/stains appear. What are they? Need I worry? I'm reluctant to get the mirror out unless it really does need a clean.

Comments/advice gratefully received.

[scarp15]

A fraught issue. Many of us seem to get paranoid about our kit, myself included!! I have a Sky-Watcher Explorer 200P. During these cold, cloud-free nights the primary mirror fogs up - and indeed the whole outside of the casing becomes wet - especially when I bring it indoors. Last night, back indoors, I noticed when I shone a light down the tube to see if the mirror was still fogged that it appeared speckled with what looked like dots/stains ... as if it had been splashed by something (I keep the cover on at all times when not in use). Naturally this morning the mirror is unfogged and in natural light seems spotless. But when I shine the torch on the surface once again the dots/stains appear. What are they? Need I worry? I'm reluctant to get the mirror out unless it really does need a clean.

Comments/advice gratefully received.

Probably nothing to feel particularly concerned about, though I can understand how this can become a little distracting, even though logically the views are unaffected.

My mirror has a few spots plus dust build up and so eventually I decided to give it a clean. I followed a similar process as Moonshane has described and swishing the water so not really having direct contact on the mirror surface on this occasion at least (as with cotton wool etc). In part I wanted to do this to overcome any anxiety I may have in carrying out a primary mirror clean. As is often said, the main requirement is to be organised, not a job to just fit in.

Now that I have undertaken a mirror clean process, whether it has been advantageous or not (I doubt it) I do at least feel I have both the level of confidence and competence to undertake this task again. Some of the spots are still there but the views are still completely fine. Mirror cleaning, might be one of those maintenance jobs to carry out in the long Summer months.

[Langworthy]

Probably nothing to feel particularly concerned about, though I can understand how this can become a little distracting, even though logically the views are unaffected.

My mirror has a few spots plus dust build up and so eventually I decided to give it a clean. I followed a similar process as Moonshane has described and swishing the water so not really having direct contact on the mirror surface on this occasion at least (as with cotton wool etc). In part I wanted to do this to overcome any anxiety I may have in carrying out a primary mirror clean. As is often said, the main requirement is to be organised, not a job to just fit in.

Now that I have undertaken a mirror clean process, whether it has been advantageous or not (I doubt it) I do at least feel I have both the level of confidence and competence to undertake this task again. Some of the spots are still there but the views are still completely fine. Mirror cleaning, might be one of those maintenance jobs to carry out in the long Summer months.

Cheers - sounds like good advice.

[kerrylewis]

Well, after 9 months of dithering, I've finally been and done it. Beautifully clean now and back in the OTA. I feel better at least! 

Just need to re-collimate and then we will see......

[garryblueboy]

Well done Kerry I've recently aquired a Orion 12 inch Dob with a rather dirty mirror and now looks like new

Just takes a little time and patience but worth it in the end .