Primary mirror repair needed

bojan · #1 10-11-2006, 10:25 AM

Hi guys,
I do not have my 10"dobson any more..

Yesterday morning, while moving the tube from one point of my front yard to another, to get the best place for taking some pictures of Mercury transit, I dropped it on the concrete floor (the tube was slippery due to some dew, and I never decided to fit the handles.... I think after this mishap it will be the first thing I will do),
Anyway, the primary mirror was damaged when the secondary hit its surface... I think it only needs re-coating (it was overdue anyway, I purchased it 25 years ago and only cleaned it 3 times).
Could anyone recommend someone who will do this job (and not charge arm and leg)? The mirror has SiO coating (I am aware this may be a problem, and that the mrror may have to be re-polished).
Thanks in advance.....

Dennis · #2 10-11-2006, 10:34 AM

Ouch - so sorry to hear of your misfortune.

If only there was a rewind button for events like this, to allow us a second chance. Good luck with fixing the damage.

Cheers

Dennis

bojan · #3 10-11-2006, 10:48 AM

Yes... rewind and especially edit button would be good... this "movie" was playing in my mind dozen of times last night... at least I know what stupid things I have done and I suppose I will never do it again (there are many other stupid things I can do....:-( )

acropolite (Phil) · #4 10-11-2006, 01:20 PM

Scott (tornado33) recently had his mirror recoated. Info in this thread

bojan · #5 10-11-2006, 01:35 PM

Thanks for this info :-)
I will give them a call straight away :-)

Gama · #6 10-11-2006, 02:19 PM

From memory Astro Optical Supplies used to do things like this (Repair), and they do recoat as well. Give them a call.

Garyh · #7 10-11-2006, 02:53 PM

Hi there,
Sorry to hear what happened...thats always on my mind if the secondary would come loose and Murthys law would dictate that it would land in the middle of the primary even if you were holding it mirror up...
Try Chi Qin Co ? he advertises in the AS&T up the back. He is in Sydney and he does a excellent job. Great price and he gives you the silicone overcoat as well. Done a nice job on both my mirrors..
Cheers and hope thats all it needs...as you will pay a bit for a polish as this will mean refiguring.
Gary

ausastronomer (John Bambury) · #8 10-11-2006, 03:20 PM

I would either go with Chi Quin Optical (Isaac) or Laserdyne in Queensland http://www.laserdyne.com.au/First.htm

CS-John B

bojan · #9 10-11-2006, 03:34 PM

Thank you very much for all this info, I feel better now :-)
Maybe I will end up with even better mirror (if they need to re-polish it).
Is there anybody in Melbourne that is doing this kind of service, simply because it may be more convenient for me to hand-carry instead of posting it to and fro?
Thanks again to all,
Bojan

nightsky · #10 10-11-2006, 03:52 PM

G'Day Bojan,
Give these people a ring they should be able to help you out, there a great mob
https://www.bintelshop.com.au/welcome.htm
and good luck to you

ausastronomer (John Bambury) · #11 10-11-2006, 04:01 PM

Quote:

Originally Posted by nightsky

G'Day Bojan,
Give these people a ring they should be able to help you out, there a great mob
https://www.bintelshop.com.au/welcome.htm
and good luck to you

They are a great bunch of blokes, I talk to them regularly. They can do many things, mirror recoating isn't one of those things, so not much point in giving them a call in this case. They would only pass you onto Chi Quin Optical(Isaac) if you did call them. Save the 10 cents in this case unless you just want to have a chat

CS-John B

bojan · #12 10-11-2006, 04:06 PM

I already talked to Bintel guys and you are right John, they could not help much with primary, but it seems they will have the secondary which I also need (part of it was chipped off when it landed on primary) .
Thanks again for best wishes :-)

Gama · #13 11-11-2006, 12:01 AM

May just be cheaper to buy new optics. As by the time you ship it both ways (Cost) then getting the mirror repolished, then recoated, well, just check out the price on some second hand or even new mirrors. Pretty cheap !.

bojan · #14 12-11-2006, 05:35 PM

Yes, I was thinking along these lines.. The only question is, how good those cheap mirrors are.. I have seen couple of pretty horrible things recently.
And of course, all will depend on what needs to be done. Chi Quin Optical (Isaac) seems to be OK and they are willing to take this job. I talked with him and I am only waiting for quotation for repolishing. Re-coating for 10" mirror is AU$ 229.00 (GST included?). The new 10" kit from Coulter optical is US$399 F5, 1/10 wavefront)
All others are either booked or not providing necessary service. For instance, Astro Optical Supplies said they will do it, but they do not guarantie that the whole old coating will go off from glass (SiO protective coating is the problem for the process they are using to remove aluminium, and they told me to order the new mirror just in case... But, those mirrors are coming from some cheap supplier from China and they only guarantie 1/4 wavefront accuracy, which is not enough for me, so I decided not to go with them).

Gama · #15 12-11-2006, 06:48 PM

You should get a mirror cheaper than that. Just go to Astromart, or just put up a wanted post here on this site.
Call up Astro Optical supplies, as they used to deal with mirrors and the sort..

Gama · #16 12-11-2006, 06:50 PM

Then again at the end of the day, if the damage is really only minor scratching and some chips here and there, then you may get away with just dabbing some black flat paint on the spots, and keep using it.

bojan · #17 12-11-2006, 07:37 PM

Yes, that is also the option... I washed the mirror today and it does not look so bad.... the impact is visible as a scratch but that is about all :-) First I have to get the diagonal, then test the whole thing... Maybe I was lucky more than than I thought possible... :-)

tornado33 · #18 16-11-2006, 10:10 AM

I would definately see Chi Quin Optical (Isaac) first, he will be able to advise what needs to be done, and he knows how to safely remove old overcoating if it does need recoating. If not done properly, removing a SIo2 overcoat can ruin the figure of the mirror as the underlying glass itself is damaged.

If the scratch on the mirror is in the middle, it wont affect optical performance at all, as it will be under the shadow of the secondary, and even if not, a scratch wont affect it much anyway.

Some decades ago in the US I think, a Uni student had a breakdown and opened fire with a gun at an observatory telescope mirror. The bullets chipped the glass, but all they did was paint the chipped areas with black paint to stop unwanted reflections, and kept using the scope as normal, the light loss neglible.
Scott

Gargoyle_Steve (Steve) · #19 17-11-2006, 04:17 AM

re your calculations on pricing repair vs new above: Andrew's list 10" primaries on their site for $499

http://www.andrewscom.com.au/site-section-10.htm
(scroll down a fair way)

Since they sell the GSO dobs I am making a bit of a leap by assuming that these mirrors are also GSO, but if so they are quoted as being 1/12th wave accurate (see the dobs description further up the same page), however I'm fairly certain they are bare aluminium and not Silicon Oxide overcoated.

Worth the price of a phone call perhaps, if it gets to that stage?

skies2clear · #20 17-11-2006, 05:08 PM

Sorry if I missed the info from this thread, but did you mention what your primary mirror was made of? You may be worrying needlessly about damage to the figure of your mirror when the SiO coating is removed, because it depends what the mirror is made of. Plate glass is a problem, but boro-silicates like Pyrex should be OK. This info I received from a reputable optical expert,

Good luck,
Nick