10" GSO Primary mirror coating

[Grahame]

Hi Guys,

Tonight I have removed and washed the primary mirror from my 10" GSO dob. Upon Finishing I took a closer look and saw "speckles" on the surface (have a look at the attached image) the droplets you see are a mixture of 70% isopropyl alcohol and 30% ethanol for quick drying and displacing water.

Is it "normal" for a coated mirror to look like this - or should the coating be more like the standard household mirror in which you cannot see these specks?

Grahame.

[Rick Petrie]

It is definitely not normal for a freshly washed mirror to have so many speckles so close together like that.
It appears as though something has been sprayed on the surface.
Has the mirror looked like this for a while, even before removing to wash?
What did you wash the mirror with and did you rinse thoroughly with water and distilled water as a final rinse.
I hope the chemicals, isopropyl and ethanol haven't reacted with something that may have been on the surface. In this case the speckled areas may be permanently etched, but not knowing your method of cleaning I can't say that for sure.
Cheers hope this has helped.

[astro_nutt]

Hi Grahame,
Just a question...have you observed when your neighbours are have a BBQ and you can smell the snags and stuff cooking away?...or....a place where road traffic is frequent and jet aircraft fly overhead?...the reason I ask this is because of the oils, sticky smoke and burnt jet fuel that are present in the air when you observe and of course find their way to the mirror's surface..
When you try to wash it off it will sometimes smear and swirl over the mirror....(like I found out the first time I tried)...it's like a greasy window...cold water and detergent will find it hard to clean.
The method I use is to place the mirror in a sink or basin that has been throughly cleaned and sterilized with metho including the sink plug!! (use gloved hands A/C the oils from your skin) filled with warm water then gradually add hot water until the temperature is around the 40 c...next add a mixture of detergent (4 drops of detergent to a cup of water and mix) to the hot water over the mirror and allow to soak for 10 minutes. Drain the basin and rinse the mirror with warm tap water followed by distilled water....clean, sterilize the basin and repeat the process but after soaking for 5 minutes swirl the mirror around the basin for a few minutes before rinsing and remove any drops of distilled water with the corner of a rolled-up tissue...whatever gunk is left behind shouldn't affect your image!!
I know it sounds excessive and it may not remove all of the greasy deposits.
I hope this helps...cheers!

[Grahame]

Hi Guys,

I followed a procedure very close to the above one in washing the mirror - did a 10 min soak with tap water, 10 min soak with tap water and detergant, rinsed off with distilled water. The specks were visable before the washing too. I have had the scope for just over a year now, with this time being its first clean.
I am wondering if the coating is somehow being degraded by time (poor coating perhaps?)

Grahame.

[erick]

Garden Island? Are you perfectly positioned for salt water spray?

[Grahame]

*grin* yes I am in the perfect spot for sea spray during the winter storms however the scope has spent its life covered with a blanket up top and a thick plastic bag covering the bottom end. :-)

if there are any other GSO dob owners out there about to clean their mirrors I would love to see some pics of it just for comparison.

[MrB]

I can see my house from up here! ;)
(no seriously, I can!)

[PCH]

Hi Graham,

some time ago I decided to give the mirror in my 12" LB a wash, and was horrified to find all manner of speckles all over it. I hadn't realised just how bad it had become until I took it out and had a close look - much the same as yours as far as I can see.

I asked here on the forum, and we more or less came to the conclusion that it was the result of a year or so's lack of care after a night's viewing. Meaning that, after use, I have always just stored the scope in the shed with the ota pointing vertically. There has always been a net curtain type cover over it. But naturally, any condensation that has formed has just sat there drying overnight, and depositing muck on the mirror surface as it does so.

I did still clean the mirror as best I could, but it does still look really quite yuk. The good news is, it doesn't seem to degrade the image quality hardly at all. Now, after use, I rest the ota horizontally in it's mount.

Hope this helps :thumbsup: :)

Cheers,

[bmitchell82]

I remember you talking to me about your problem, did you just soak the mirror or did you actually try and remove the gunk with light strokes of cotton wool balls? I remember from being up north we used to go fishing and the salt would stick the the hull of the boat it was almost like sand paper it dried so hard. it sucks that you cant get the mirror nice and clean :(... how long till the new scope comes around.?:D

[multiweb]

I have something similar on my 5" newt. Not as pronounced but it doesn't seem to do anything optically. I haven't seen any difference anyway while imaging. I guess dew on and off over a period of time does build up some kind of deposit. You can try a bit of acetone on a very small area see if it makes things better.

[marki]

Do not use alcohols on the mirrors, they will react with the Al and stuff them unless your coatings are good enough to prevent contact.

Mark

[Grahame]

hm.. lots of food for thought here - I have never kept the dob in any other position than vertical. That has now changed. Also I did the "every so softly" cotton wool thing going round the mirror from center to edge and although the mirror is looking so much better than before the spots remained.

Quick star test last night and have great diffraction spikes again visually, moon was very sharp also.

I believe the alcohol I used was not the cause - as i kept a close eye on the mirror at all times of the cleaning process.

I was also under the impression that isocol (used during the final stage to displace water left on the mirror) was 70% isopropyl alcohol dissolved in ethanol (no additives included apart from these)

Lessons learnt so far:

1. Never store a dob in the vertical position
2. Clean mirror more often than once a year!
3. Inspect all telescopes upon purchase and record condition of mirror/lenses for future reference :)

[Tandum]

Grahame,
All my newt mirrors looked like that after pointing up outside. I never worried about it :)

[Grahame]

Hi Robin,

Guess its going to happen - never expected to see a mirror go like that though :shrug:

Just biding my time until the 10" RC's from GSO arrive in Aus now :D

[Tandum]

Grahame,
Cripps mate, I've heard enough 8" horror stories to put me off. Pmrid is sending his back to tiawan on his own buck to get it fixed. Looks to me if you get one you're on your own. The locals can not support it.

You may as well get it off shore....

[Grahame]

Robin,

long story short - had an 8" and returned it (was F9 version) not f8. it was a nice scope and I believe the extra time GSO has put into the 10" should be worth it - hopefully they learnt a thing or two from the production of the 8" version...

time will tell - I believe the US will get the first shipment from GSO, just waiting for the reports to be posted in next month or so.

[Tandum]

Double post ... alex tells me that people in the US already have the scope and are imaging with it. Search CN forums.

I don't want or need one :D

[Grahame]

ooohhhh this is news - i have been unable to find any references to the 10" so far :(

for the type of photography i want to do the longer f/l in such a small package (compared to a 10" dob for instance) is perfect :thumbsup:

[Tandum]

Isn't it only like 1800mm? The dob would be like 1250mm?

I would have though something like around 3meters would rok your soks :)

It's most likely an orion 10" on CN. I can't search there.

[Grahame]

Thats about right for the focal lengths, however without a permanent home the traveling setup it what im stuck with for now :(

how i would love to have a sturdy pier based observatory setup!!

[Tandum]

Don't rush into anything. Let alex test it first :)

I have a pier here but I keep spending money on crap rather than concrete.

[CoombellKid]

I brought a 16" primary direct from GSO which is now showing similar to
what is happening with yours. I figure they just dont do quality coatings.
Especially when you consider that the mirror only cost a couple to a few
hundred dollars than a recoat would cost here.

So I'm not too worried about it. I dont think it has effect the views. And
when it does I'll get it recoated. Maybe even send it to someone and
have hand figured first.

Cheers,CS

[bmitchell82]

I guess they have to do something to change it up between the brands! most everything comes out of syntas factory. my SW mirror has been stored in the upright position since the day i brought it mind you always had the cylinder cap on and sat on foam to stop the spiders getting in (... lernt my lesson after a daddy long legs thought my 10" tube was the shiznit!). its nearly a year old now and my friends always comment on how clean it is and i have cleaned it once or was it twice? I feel sorry for your 10" greahame itll feel neglected once the new kid comes in :)

[erick]

A couple of shower caps are your friend - over the mirror end of a reflector! Keeps the creepies out.

[Grahame]

Cheers CS, I have not noticed any drop in quality of image so same as yourself there. Within a month I'm predicting the 10 will be put back in it's box for visual work only with the birth of the new RC shortly.

Shower caps all round Now too!

[bmitchell82]

hehehe i would have thought you would have the RC in a sealed aluminium case with dessicant pads and a stabilized temp environment :) hehehe that would have to be your pride N joy :)