cleaning a primary mirror

matt · #1 29-11-2005, 02:48 PM

Anyone know of any threads on IIS on how best to clean a primary mirror?

rmcpb (Rob) · #2 29-11-2005, 02:57 PM

Matt,

Have a cruize thorugh this thread in CN.

http://www.cloudynights.com/ubbthrea.../o/all/fpart/1

Cheers

matt · #3 29-11-2005, 03:12 PM

Cheers Rob

How's the weather over where you are? I'd imagine the same as here. Lousy

I wouldn't like to try and remember the last time we had two good clears nights back-to-back here in Canberra

There's talk it snowed yesterday at Thredbo.

I know. It's great to see the rain. Great for the farmers. Great for the gardens. Great for ducks.

But could we have just one clear ... 9/10 seeing night sometime very, very ... very soon?

iceman (Mike) · #4 29-11-2005, 03:29 PM

There are many threads on IIS discussing it already, just do a search!

matt · #5 29-11-2005, 04:30 PM

OK. Thanks Mike. I just thought I'd ask. If that's OK?

matt · #6 29-11-2005, 04:31 PM

just spotted the "Search" facility at the top of the page

davidpretorius · #7 29-11-2005, 04:41 PM

this is just a joke following: "remember, use steel wool to remove those stubborn ground in dirt marks:

the above is a joke and do not do it or try it or even think about doing it!!!!

it is to inject some humour into this dry old forum. I remember a time back in the late 1920's when this forum was fun and had no useful info in it at all!!!!!

now, i am constantly tied up talking steppers and cooling issues.

geee, where's ken when you need him...... oh yes, he is doing something astrinomical on eq mount

where's asimov......... oh yes, he is playing with his toucam

where's ving and houghy and that larrikan bird who used to post those naughty pictures............oh well time stands still for no-one!!!!!

matt · #8 29-11-2005, 04:48 PM

Naughty pictures? Hello?

Robert_T · #9 29-11-2005, 04:55 PM

my advice from bitter experience is "don't do it".... unless it's really really dirty you're probably not gaining much and you can do a lot of damage...

cheers

Robert_T · #10 29-11-2005, 04:56 PM

oh and by "dirty" I'm talking about the mirror not the pictures OK

davidpretorius · #11 29-11-2005, 04:59 PM

mine is real cruddy, but would not know it from viewing thru it!

davidpretorius · #12 29-11-2005, 05:03 PM

ken cleaned his at star camp, it looked as easy as pie!

so get ken or striker to advise you, but it you sould be fine.

it is just - do you really need it to be cleaned????? has bird left a dropping on it or some other practical joke that we know bird can do from time to time???

bird (Anthony Wesley) · #13 29-11-2005, 05:29 PM

Hmm, DP have you skipped your meds again??

Matt, lots of people have different ideas for mirror cleaning, here's what I do:

- Go to a service station and buy a couple of "Diggers" brand demineralised water bottles, that stuff leaves no deposits when it dries. It's sold at petrol stations for people to use in their radiators but it's also good stuff for cleaning optics.

- FIll your sink with normal tap water, mix of hot and cold until it's warm but not hot, stir in a small amount of dishwashing liquid and then sit the mirror in there for about 20 minutes or so to let any grease loosen up.

- Hold the mirror underneath and rock it around so that water sloshes across the face, keep it under the water while you're doing this. Do this for a few minutes.

- Let the warm water out and before the mirror dries (i.e. straight away!) rinse with the demineralised water. You might use all of a 2L bottle, but make sure you've displaced all the tap water off the glass.

- Stand the mirror on it's edge and let it dry. The mirror should be warm all the way through from the long soak, so the water will evaporate after just a couple of minutes, and leave no residue.

If you go through this and then see that the mirror still has crud on it then you have to repeat, with slightly more vigorous sloshing at the appropriate stage.

If it seems to have crud firmly attached that won't come off on its own then you could try a *careful* clean while it's under the warm water, but you have to be very careful not to scratch the coating. In practice a little bit of stuff left on the mirror will make zero difference to it's performance so I personally wouldn't worry if you can't get it completely clean.

regards, Bird

iceman (Mike) · #14 29-11-2005, 05:54 PM

Matt, of course I meant the "search" facility, just type in "mirror clean" and there's a thread I remember where people discussed their varied and different methods.

I've done just that, and found the thread I was talking about.

My thoughts (in that thread) contradict with Robert_T's above, but it doesn't mean i'm right and he's wrong.. Everyone is free to make their own choice.

Have a read and see what you think, to me it's not scary to clean a mirror (I did mine again 2 weeks ago) but for others it can be.

Louie and I had a discussion about it the other night, his opinion is similar to Robert's, so it just goes to show that in the end you'll need to make up your own mind

davidpretorius · #15 29-11-2005, 06:09 PM

medicine fixed now,

i like that bird, very straight forward! i am going to get myself some demineralised water!!!

asimov (John) · #16 29-11-2005, 06:11 PM

As has been mentioned before.....Unless it has a LOT of dust & crud on it, it really is not necessary. Prevention is really better than cure. I keep my OTA horizontal at all times unless I'm using it of course.

2 years & counting my mirror is clean as a whistle....discounting a small dust coating which is nothing to worry about really..Looking at a primary mirror using a torch is a no no...

matt · #17 29-11-2005, 06:31 PM

Thanks guys

Mike. I found the threads you were talking about using the "Search".

All very handy. I'm not really that desperate to clean the primary. I was more just asking the question in case I decided it was necessary.

One of the recent mods I've done to my scope was a very good suggestion by Bird, to trim back the clips to leave no area overhanging the primary.

Instead you use a little bathroom silicon in between what remain of the clips and the primary to hold the mirror in place.

This has had a dual benefit: I don't get large black areas (the clips) in my field of view when the eyepiece is racked inside focus, nor is there any possible tension on my mirror from overtightened clips.

I must say there has been an improvement in my inside focus star tests which you may remember I'd had a few issues with?

But the problem was I somehow got some very tiny "flakes" of white silicon on my primary which when I tried to ever-so-lightly brush (using a soft camera lens brush/blower) away actually smeared

The flakes hadn't fully dried and created little white streaks on my primary.

Fearing possible corrosive effects, and more obviously the fact that streaks on the mirror are not a good idea, I VERY gently wiped them off with a ultra soft camera lens cloth.

All trace of the silicon streaks are gone, but I'm left with a very small amount of lint as a result. The camera cloth had been recently put in the general wash, as per instructions for periodic cleaning of the cloth.

Boys .... what a series of events!

I'm almost certain the mirror's OK ... but you never know? I've had it out to have a close look for scratches and other signs of wear and tear but it appears to have come through unscathed. Although there's no knowing what effect the whole episode has had on the coating????? Time will tell.

I've not seen any visual evidence of any problem so far

asimov (John) · #18 29-11-2005, 06:43 PM

You know, I'd LOVE to know exactly how much dust could be on a primary before it becomes 'noticable' at the eyepiece. And what about astrophotography?? I wonder if this is less tolerant of dust on a primary mirror.

Sorry to hear about your bathroom silicon prob Matt, HOPEFULLY your mirror will be none the worse for it.

slice of heaven · #19 29-11-2005, 08:21 PM

Quote:

Originally Posted by asimov

You know, I'd LOVE to know exactly how much dust could be on a primary before it becomes 'noticable' at the eyepiece. And what about astrophotography?? I wonder if this is less tolerant of dust on a primary mirror.
.

That's a good question John.....we need a dirt-o-meter to check it.

I'm fairly regular at cleaning my mirrors...1998-9,chasing Pluto...2000-1 crazy Comet chasing bug....2003..Mars......2005..Deep Impact.
Yep, every couple of years whether it needs it or not

.
There IS a difference to be seen afterwards and this is a scope that is well sealed when not in use.

Doing Imaging I'd expect it would pay to be more fastidious and wash it more often.

asimov (John) · #20 29-11-2005, 08:37 PM

Hmmm..That's very interesting Slice! Naturally Once I read this thread I went & checked out my mirror......just like I usually do when I read something about cleaning mirrors.

Gets me all concerned.....AGAIN....STILL....wha tever.

Had a good look at the mirror with no light shining on it....doesn't need cleaning. Shine a light on it & OUCH!! Take it out & clean straight away!!

I've now made a pact with the said mirror to take her out in 1 years time to clean it!