Mirror Cleaning

Hello once again!

I've had my LXD75 6" for about four months now and I just noticed the other day how absolutely filthy the mirror is!

I was wondering if any of the more experienced astronomers out there would do me a massive favour and maybe outline a few steps to cleaning a mirror without totally fecking it up? I am no where near confident enough to try it without some advice, also collomating the mirror after taking it out and putting it back in seems like rocket science to me. Anyone help?

PS sorry for all the questions!

Jose - when you say its "filthy", how did you determine this? If you shone a torch onto the mirror and noticed all the dust specs or if you looked at it in broad daylight then I would recommend you don't touch it.

Looking at optics in bright light will show up loads of stuff that actually doesn't translate into poor performance when viewing the night sky. My mirrors have been shockingly grubby when shining a torch into the OTA but there has been no discernible degradation of my images.

Really, the only time you should clean a mirror (or any optics) is if there are significant deposits of crud on them or (in the case of eyepieces) huge grubby fingerprints. By crud, I mean deposits other than dust.

If you really must clean the mirror becasue of crud, you should have a swan around the internet (telescope cleaning in google etc should find some links) and find a comprehensive procedure. There are a few really good ones out there (Astro-Physics springs to mind).

If you've not disassembled an OTA before or done any cleaning, you'd be best doing in conjunction with a club colleague or another astronmer who has already carried out the task.

Do you know how old the mirror is by the way? If you bought it new and have only had it four months, I'd say leave it for a few years unless a bird has left a present on the mirror...

Dave

Hi Jose,
When you say your mirror is filthy ,how "filthy" is it ? is it light dust or something else?

Just saw Daves post ,TOTALLY concur,wouldn't touch it ,just make sure to keep dust cover on when storing.

Eugene

Hi Jose,
The most dangerous thing for a mirror is over cleaning !!
At most, under normal conditions, you should clean a mirror only once a year. If the tube in enclosed like a SCT, then it should very rarely or never need cleaning. I've never cleaned my 7 years old SCT mirror, but I have on occasion cleaned the clubs 13" mirror and my own 20" mirror without destroying them.
Shining a bright light on any mirror will show disturbing dirt and other gunk, so do not worry about that if you see it.

If you see really bad hazing/dulling of the mirror under normal illuminated sitting room conditions from directly in front of it from about 5-10 feet away, then you should consider cleaning it. What kills the image brightness is a smeared mirror or a very thick layer of dust!, so imagine that you stroked your finger along it (don't do this BTW) it would collect alot of dirt, like on some old wooden furniture.
Specs of dust here and there have absolutely no effect on the image.

If you are going to clean it, then this is what you should do (or atleast what I do)
Get 3 5litre cartons of pure (distilled preferably) water from your local chemist and a big roll of sterile surgical cotton (nothing added to it).

1, using the first container, wash down the mirror to get all the grid off it, you cannot wipe the mirror with this grit on it as you will certainly scratch it! Buy another carton if necessary depending on the state of the mirror. Placing the mirror at 45 degrees would be ideal.

2, Put one drop of washing up liquid into the second carton and shake vigorously, and I do stress literally only 1 drop!!!. Pour half of this all over the mirror giving it a good soaking.

3, Using the cotton, give the mirror a very soft rub using only the weight of the cotton, do not press hard!. Wipe from the centre to the outside.
Never use the same piece of cotton twice. You're going to use alot of cotton here. Pour the solution from step 2 while doing this. Don't use dry cotton.

4, The water will run cleanly down the mirror when it is clean, it should not collect as alot of water drops, if it does, then it is still dirty. Repeat steps 2 and 3 if needed but do not go overboard.

5, Pour the third container of water over the mirror to get off the washing up liquid solution. Then using the cotton stroke the mirror like above using new pieces to dry it off.

You will know if your mirror needs recoating if you see specs of brown rust like dots on it. What happens is that any dew that forms on the mirror is in fact a mild acid solution (collected from crap in the atmosphere) and literally corrodes the metal coating. Infact when a mirror is re-coated, the original coating is stripped off using acid, so you get the idea.

If you have a dulled mirror, it means it was not cleaned properly, not much you can do to fix it,as it might be now covered in micro scratches.

If you have a slight blue haze over the mirror it means that too much cleaning solution (washing up liquid) was used and only alot of water and careful wiping will remove it.

So I hope this makes sense to you, basically do not clean the mirror unless you absolutely have to.
BTW, nothing collects dust more then a clean mirror :lol:

Look's like ye were right! Only a light smatter of dust here and there... But there are four solid black spots about a millimeter wide on the lower left of the mirror- they actually look like the southern cross! I've tried tuning the tube upside down and giving the back a light tap but they won't budge. Anyway I don't think they are affecting my image...

thanks for the help lads and sorry for the false alarm :oops: