Whats the best way to clean a mirror?

gregbradley · #1 20-02-2011, 11:25 PM

I may need to give my CDK17 primary mirror a clean soon. Its got a bit of dust buildup on the mirror. One of the weak points of an open system.

Any suggestions about the best way to clean the mirror?

I was thinking of having the scope horizontal and lots of soapy warm water and daubbing it with a soft sponge cleaning the sponge often.

Then rinsing with distilled water and blow dry or let air dry.

I would allow the excess water to simply run down the OTA tube and lean it forward slightly so it drains onto the ground. The OTA tube is not that long being a truss scope, perhaps 350mm.

Greg.

Saturnine (Jeff) · #2 21-02-2011, 12:12 AM

Hi Greg

Just a thought, not actually having to resort to this method as my newt mirrors are removable and being reluctant to touch a mirror surface with a sponge especially something like your CDK17. Would be worth a try to buy a new spray bottle from a supermarket for about $3 and fill it with warm slightly soapy water and with the scope laying horizontal, mirror vertical, spray the mirror to wash the dust away, may have to do it a few times for stuborn stuff. then you can refill the spray bottle with destilled water and rinse away the soapy stuff.
After that , just let it air dry or blow dry if your wish, good luck.

Jeff

Gama · #3 21-02-2011, 12:19 AM

Hi Greg,
You have the little sister to my Planewave scope

.
I had the same issue about a year ago, but i came up with an answer.

What i did was to move the scope so the mirror was vertical, and the scope pointing slightly down.
I then used some thin flexible plastic sheet (Like the plastic used in the front door take away shops, and wedged it between the mirror and the cell wall. this way the plastic sheet will bend to an arc shape and its wide enough that it curves around more than half the mirror and long enough to stick out the front. This plastic sheet will allow the water to run down its length to outside the scope where it falls into a large plastic tray, so it doesnt make a mess on the floor.
I then use a plastic spray bottle with a mixture of detergent to spray on the mirror, and allow it to soak a little. I then used those cheap dusters that look like candy floss on a stick, and soaked that into some detergent as well, an i just let it sit on its own weight while gently moving it around, while spaying ample of detergent/water mix on and around it. I then just used distilled water in another larger "Pump up" spray bottle, this way, once the bottle is pressured (By Pumping it up) i just need to point and spray the water to clean that section without my hand getting tired sqeezing the trigger.
I do this one sction at a time, then i rotate the scope to do another section, and move the plastic sheet to the next section to continue. I also use foam between the Baffle and the centre of the main mirror so no water leaks down in there. You should be left with a clean mirror..

I would love to use the polymer spray, but because my mirror has a rubber edge on the mirror, i think it may destroy/deform it.
The polymer is by far the simplest and fastest, but due to the rubber ring, i cant use it.

Theo

beren · #4 21-02-2011, 12:21 AM

I use a combination of these two methods 1 2

astrospotter (Mark) · #5 21-02-2011, 08:30 AM

I agree that the sponge is not a good thing at all. Grit will stick in the sponge even if you rinse it. You must use something that can hold a lot of water and you can use fresh ones frequently to minimize any risk of grit in the 'wiper'.

Generally I do something similar to Gama's method but use the cotton balls found in a cosmetic department with a big bag fairly cheap. My mirror comes out so I don't have to do the plastic sheet thing but that was a smart way it seemed to catch the water/soap.

I use very small amount of very gentle dishwashing liquid (not much at all) in slightly warm distilled water. Important to use distilled water to avoid tap water grit from your spiggot/pipes.

Don't do this on a hot day or with ANY chance of sun hitting the mirror through a window (later as it is trying) or outside as the sun moves in the sky. Other reason for not a hot day is that soap stage to dry on the mirror and leave residue that you will then have to 'chase'. ALWAYs do in total shade. I have found that a big mirror can easily focus and burt very quickly anything at it's focal length. Fun for when you are a kid but NOT fun generally for eyes or safety. I share assorted stories with others and trust me, NEVER let the sun hit your mirror in transport to a site, in scope setup in the day, or in forgetting to cover it at night OR in cleaning. It's just 'bad' idea. I have a friend who cleaned scope mirror inside, set it to try and sun moved in to the window and he notices smoke cause the mirror focused on a bookcase nearby. No fire as he was there but it COULD have been real nasty situation to explain to the wife.

Rinse first and let soak for a minute then with mirror at a 30 degree grade angle start at top with GENEROUSly soaked cotten balls and do small area with only the weight of the cotten ball (don't push down on those) and rotate the cotten slightly as you push it so if it does pick up any grit it is lifted and not pushed back on the mirror to grind in a scratch.

Disguard the cotten balls you use rather fast so you don't re-apply with small grit from last pass and always use a LOT of the warm water. Work your way down from the higher part of the mirror to the bottom (let gravity help you drain off the grit).

After this use distilled water and rinse the mirror with trickles of the pure water to remove all soap film. Do this rinse at least twice.

Lastly there are MANY people who claim to not clean a mirror till it gets fairly bad because it is greater risk than reward. This is sort of true but if you have a real nice quartz coating on your mirror it is less of an issue than if you are going to be contacting the Al directly. A non-quartz coated mirror I would say to avoid cleaning too often.

This is obvious but be real careful to not have anything at all that might accidentally drop on the mirror (empty pockets if you have shirt pockets) and have short sleeve shirt to avoid cuff rub and so on. For the ladies, keep your hair tied back.

astro_nutt · #6 22-02-2011, 11:47 AM

Before I cleaned my mirror. All jewellery is removed. I made sure that the laundry tub was scrubbed clean including the plug and tap. The curtain was removed also. The mirror is given a dust off with canned air then placed in the tub and gradually filled it from the hot tap until the water temperature reached about 40 C. A 50/50 mixture of baby shampoo and isopropyl alcohol is mixed in and let the mirror soak for about 5 mins to allow the oils/grease to lift from the surface. (If you live in the suburbs you can bet that exhaust pollution, jet fumes and smoke from a neighbours BBQ will find it's way to the mirrors!) The mirror is then swished around for a few minutes. Rinse the mirror with warm tap water then drain the tub. Another mixture of baby shampoo and warm distilled water is made up in a bowl with a dozen or so cotton balls. Hold the mirror at an angle in the tub then clean the surface by drawing and turning the cotton ball under it's own weight in one direction only then
discard after one application across. Rinse in warm tap water then with distilled water and allow to dry with the mirror near verticle. Any remaining water droplets can be touched off using a corner of a tissue. Allow to cool completly before reinstalling.
Cheers!

g__day (Matthew) · #7 22-02-2011, 03:05 PM

I was think about that plastic sheet and an idea hit me - could you use static discharge + compressed air to shift dust from your mirror to the sheet?

I pondered if the mirror was vertical and the sheet was too and was say 20 mm away - could you staticly charge the plastic sheet so dust would transfer from the mirror to the sheet? Secondly if you blew compressed air it should help remove most dust.

Anyone ever try this approach?

I seem to recall reading that professional labs use carbon dixode to clean large mirrors.

gregbradley · #8 22-02-2011, 04:28 PM

Some great tips there. Thanks very much.

I cleaned my RCOS mirrors once but that involved removing it from the
tube (a closed tube). That meant recollimation etc (not really that hard though).

I'll clean it soon. I like the cotton ball approach (I have used that successfully on APOs) and rinsing with distilled water. Its really just a bit dusty and not affecting the images or at least I don't think it is. So no real urgency but good to know.

Thanks.

Greg.

dannat (Daniel) · #9 22-02-2011, 04:49 PM

The can of compressed air will work well ( use it for bino objectives)
NB do not getvthe can too close to the optical surface...the propellant can be discharged, I'm talking within 10-15 cm, hold the can back farther than this it gets rid of a fair bit of new dust

floyd_2 (Dean) · #10 22-02-2011, 08:33 PM

I use the distilled water approach as well. When I had an obsession, I cleaned the primary while it was still in the mirror box and just lined the mirror box with black plastic so that the water could fall away.

1. I used a puffer brush to get rid of any grit on the mirror first.
2. Next I'd fill a spritzer bottle with distilled water and a single drop of washing detergent.
3. Tilt the mirror at close enough to vertical and spray it with the distilled water repeatedly, and let the water run off. That got rid of any contaminants that could cause damage in the next step
4. I put the mirror box back to the horizontal position, and filled the mirror with distilled water / drop of detergent solution and let it stand a while
5. Tilt the mirror and let that water run off, and spritz it again
6. Fill the mirror in the horizontal position once again, and then use strips of cotton wool (the sort that you buy in rolls) and gently drag them across the surface of the mirror under water...only under their own weight.
7. After one pass, discard the cotton wool and get a fresh piece. Continue on until the mirror has been gently wiped clean
8. Tilt the mirror and spritz it again
9. Keep the mirror tilted and let it dry, using the corner of a kitchen towel to wick up any droplets that remain

It sounds like a laborious task, but it's easy. If you can remove the mirror it's a little easier, but you have to be a little more careful handling the mirror out of its cell.

I have noticed that the mirror in my XX14i is getting filthy as well so will be cleaning it soon. I think its been getting condensation in the mornings and am still coming to terms with what I should do to combat this.

Dean

leinad (Dan) · #11 22-02-2011, 08:51 PM

Has anyone tried Photonic cleanings First Contact products; im keen to try their product in the next few weeks.

http://yhst-44888210506633.stores.ya...yproducts.html
http://www.photoniccleaning.com/appl...ns/telescopes/

TrevorW · #12 22-02-2011, 09:22 PM

Get out the hose, spray on some Windex then give it a good old squirt down then dry with some lint free cloth very gently then finish with a hair dryer, geez its not brain surgery

leinad (Dan) · #13 22-02-2011, 09:42 PM

Quote:

Originally Posted by TrevorW

Get out the hose, spray on some Windex then give it a good old squirt down dry with some lint free cloth gently then finish with a hair dryer, geez its not brain surgery

I'll give this a go when I get my $10,000 scope.

TrevorW · #14 22-02-2011, 10:06 PM

Oh I forgot remove scope from mount first, water and elctronics don't go to well.

leinad (Dan) · #15 22-02-2011, 10:18 PM

I suspected a bit of pun Trev.

Seriously; it's a mixed bag of procedures out there for cleaning telescope mirror optics.

Windex has been recommended for cleaning lens; and in some cases using a diluted solution for cleaning and maintaining reflectivity of the mirror.
Though Windex is reported to have some heavy impurities; that over time are reported to eat away(be corrosive) at the mirror coatings and in some cases cause fogging and more streaking then intended during the cleaning process.

A real pain in the a$$ that one might want to avoid.
There's so many recommendations and caution out there it's not funny.

TrevorW · #16 22-02-2011, 10:27 PM

I recently cleaned the mirror on my RC although a lot smaller with camera lens cleaning fluid and lint free lens tissues, it worked a treat, figured good enough for my camera lens should be good enough for my mirror

gregbradley · #17 23-02-2011, 07:12 AM

Bintel sell a lens cleaner that is really good and I have used that for several years.

Washing the mirror horizontally would not be a good idea here as the CDK has a hole in the mirror like an RC where the primary tube goes through it. Water would go inside and perhaps on the focuser/sensors for temperature etc.

Greg.

Logieberra (Logan) · #18 23-02-2011, 10:35 AM

Personally, this is my favourite method:

http://www.iceinspace.com.au/63-345-0-0-1-0.html

astronut (John) · #19 25-02-2011, 04:12 PM

I have just had my 12" mirror recoated by Isaac from Chi Qin.
I asked his advice on the best method of cleaning a mirror.
His reply was to .........place the mirror under the tap (in a clean sink, away from chemicals etc) run the water over the mirror to remove most of the dust and dirt. If there are any stubborn "bits" very gently run "medical grade tissues" (no scent or other chemicals impregnated into the material) gently along the area affected.
Rinse with tap water, final rinse of 70% Ethanol (Bunnings) and leave to dry..this takes approx 1 minute.

Depending on how dirty your mirror gets...he recommends cleaning it this way, approx twice a year.