Mirror Spots Appearing???

[pat]

I cleaned my Orion mirror about a year ago, to remove the dust build up. It was gently cleaned with mild soap and distilled water.  The scope has been stored outside completely sealed and covered, when not in use. Looking down the tube the other day. There are irregular round gray spots across the surface. When using a flashligh it is horrifying. Could it be a fungus? Of all the many years, I've never seen anything like this. Should I clean it again next year?  Thanks, Pat

[Northern Soul man]

Hi Pat, if its anything like me it would do my head in!!, not sure where you live, but I know the scope is covered outside, but is there any Sun on it during the day, this would create a "greenhouse" affect - with the heat of the Sun, then cooling when in shade, it may form dew in the sealed environment where your scope is kept, you only have to look at a garden chair cover, in sunshine after a dewy morning the cover begins to dry out with "steam" coming off it.  I dont have a Newt anymore - so not sure if its moisture spots or fungal spots - if the latter, if I were you I would see about cleaning the mirror now - I keep my SCT to as close to the outside temp as possible, but stored in a dry place out of direct sunlight as to keep the temp as constant as possible - hope you get it sorted keep us informed.   Paul.

Edit - sorry Pat, the actual mirror is way in front of the focal point - so, when focused, the "spots" are well out of the "way" - there may be a little loss of light/reflectivity, but nothing to worry too much about.  The flashlight test is nothing to worry about it just makes it "look" bad, try cleaning the mirror again now and see if the spots disappear - if so - great, but if not the mirror may need a re - coat if its fungal as this will eat into the coating.

[ronin]

I suspect that the aluminium has been attacked by the atmosphere. How long a surface will last is dependant on how well done, the protective coating, environment and likely other minor factors.

The atmosphere tends to be acidic, moisture and CO2 make a weak carbonic acid. Also when a manufacturer says (for example) 10 year mirror life that is probably if kept in a sealed, temperature and environmentally controlled room. Met this once on something critical.

If it is a fungus then get it stripped and resilvered. Fungus can eat in to an amazing number of things. It will most likely be either damp marks on the surface or corrosion, but you do not want whatever to eat into the glass substrate.

The only real option I can see is get something to clean the mirror with and see if the marks go away. If they do then whatever it is/was was on the surface only, if they do not then it is deeper and will need a further decision from you concerning what to do next.

[pat]

I will attempt to clean the mirror today. If the spots are stubborn I will try steril cotton balls soaked in 99% isopropyl alcohol and roll them across the spots. Or use my finger tips to massage the mirror, as I've seen in a video. Guess it couldn't hurt at this point.  Thanks for your help, Pat

[swamp thing]

Put it this way if the marks don't come off. I shouldn't worry about fungus damaging the mirror itself. The coating maybe toast but the mirror will be fine.

My 10" mirror had a herb garden growing on it when I got it. It was teaming with fungus. I had it stripped and recoated. Job done. It performs flawlessly now. Re-coating is a pretty cheap procedure. Nothing to lose sleep over.

[Scott]

Put it this way if the marks don't come off. I shouldn't worry about fungus damaging the mirror itself. The coating maybe toast but the mirror will be fine.

My 10" mirror had a herb garden growing on it when I got it. It was teaming with fungus. I had it stripped and recoated. Job done. It performs flawlessly now. Re-coating is a pretty cheap procedure. Nothing to lose sleep over.

just curious Steve, How much is pretty cheap? I don't need it yet (maybe never) but as I say....Just curious

[swamp thing]

My 10" was about £30 if I remember correctly. That was about 5 years ago.

Recently had my 20" done that was only £140 thats about 4 times the 10" area.

[Peter Drew]

I'm currently building a binoscope using two elderly OOUK 8" F6 OTA's. Both primary mirrors were in need of cleaning and pretty spotty and being as they will be recoated in the near future there was little to lose by attempting to clean them in the meantime. I  gave them a wash with water and a drop of washing up liquid using just the weight of a cotton wool ball to stroke the surface. After a rinse with clean water and a final one with distilled water they were a lot brighter but the grey spots were still evident. Once thoroughly dry I rubbed the spots with dry cotton wool using considerable pressure and the spots were removed without any damage to the rest of the surface. 

[Alien 13]

As a long time photographer i know fungus is bad i dont know its effect on mirrors but it can spread and if it ever gets on a lens then it will eat it, that includes camera lenses eyepieces etc.

[pat]

Hi Paul,

After a good soak and power wash. Then looking directly down the smudes were hardly noticeable. And the mirror had a good reflectiviity. At a lower angle they became visable, but not as much. Then applied some alcohol to a cotton swab and rubbed one near the center of the mirror. This helped even more.

Rather than let an O.C.D. take over and prevent possible scratches on the mirror, I decided to leave well enough alone. I will keep the mirror inside and flock the back portion of the tube. Thanks, Pat

[Hartmann]

Good news

A good advice is have the mirror sealed in a box in low moisture,  relative humidity or dry conditions to prevent fungus