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Equipment Discussions >> Reflectors

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aatt
sage


Reged: 07/26/12

Loc: CT
Depressed-accident with my new mirror
      #5526419 - 11/18/12 04:26 PM

I was up till dawn the other night having a blast with my new week old 15" Discovery split tube and upon removing the upper tube assembly, one of the studs came loose unexpectedly and fell on the mirror....I am still cringing and totally upset by this stupid lack of foresight on my part.I could not believe the horrible sound of clinking metal followed by sound of the stud rolling back and forth across the formerly pristine smooth surface of the mirror. The mirror is damaged in four places. I took the cell out today and took a magnifying glass to the marks. The glass looks kinda crushed/cracked and the figure of the mirror seems to be distorted past the periphery of the worst divot by about 4 mm judging by the reflections. I can't see any spiderwebbing. Upon loosely measuring these areas my worst case scenario is 2% of the area of the mirror is compromised, but it is probably closer to 1%. Last night I took it out and it did not seem the same, but seeing was pretty bad or was it the damage? This accident is playing with my head and perceptions possibly. My collimation accuracy seemed about the same as before the accident-if not better. Does anyone have suggestions about how to evaluate this damage or what to do? I did a star test and if I tracked the defocused star across the FOV I could locate a couple of bullseyes that corresponded to the location of the strike points. Seeing was poor and the image was boiling-could not make out the rings with any consistency. This just sucks! I have had the scope a week. Hindsight is 20/20.

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Mirzam
Post Laureate
*****

Reged: 04/01/08

Loc: Lovettsville, VA
Re: Depressed-accident with my new mirror new [Re: aatt]
      #5526438 - 11/18/12 04:35 PM

Can you provide a picture? Most of the damage is probably superficial coating damage and will look a lot worse that it is. How heavy was the object that fell on the glass? If it was just a metal bolt, you may have a small crater somewhere, but I doubt that any important damage to the mirror figure would have occurred.

JimC


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aatt
sage


Reged: 07/26/12

Loc: CT
Re: Depressed-accident with my new mirror new [Re: Mirzam]
      #5526477 - 11/18/12 04:58 PM

Not at this time-my Digital camera is on the fritz and my phone is a dinosaur. I will look into it.The stud weighs less than half of a typical 10mm eyepiece-not heavy, but heavy and hard enough.

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dpwoos
Pooh-Bah
*****

Reged: 10/18/06

Loc: United States
Re: Depressed-accident with my new mirror new [Re: Mirzam]
      #5526495 - 11/18/12 05:12 PM

I don't think there is any reason to believe that the damage isn't localized to a very small area. Blacken out those spots and see how it performs. Too bad that it happened, but the actual impact will be very, very minor and in the dark only you will know.

Unless you are a "collector", I suggest that you view all of the dings and smudges and range marks that accumulate over time as signs that astronomy is going on - a sometimes messy endeavor!


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mayidunk
Don't Ask...
*****

Reged: 02/17/10

Loc: Betwixt & Between...
Re: Depressed-accident with my new mirror new [Re: aatt]
      #5526545 - 11/18/12 06:10 PM

Wow! That is horrible to hear, but I don't think it's as bad as you think it is... I believe that the major concern would be light scatter caused by the damaged areas, the mirror's figure itself is unlikely to have been affected. The MacDonald Observatory in Texas has a large reflector that has several repaired bullet holes in the primary! IIRC, I believe they painted the holes black in order to eliminate them scattering the light, resulting in the only negative affect being the overall brightness of the image having dimmed by an insignificant amount; as if the diameter of the mirror was decreased every slightly! As far as I know, they continue to use the repaired primary to this day.

That being said, you might first try calling Discovery and asking them what they would recommend you do. You could ask them about your dabbing non-reflective black paint on the damaged parts. Then, after the paint has dried, try doing a star test to see if the figure has been affected in any appreciable way. Chances are that you'll find that the star test looks just as good as it ever did. The paint dabs should no more affect the image than the secondary spot currently does. If, however, you find that the figure might have been affected, you could then determine if it appreciably affects your being able to see the objects you're looking at the most with that scope. If you do mostly deep sky, then it may not really affect it at all. If planets are your primary target, then only you can determine if the affect it has on the view is worth the cost of re-figuring or replacing the mirror. If you can afford it, perhaps it would be an opportunity to get a premium mirror, though from what I understand the mirror you already have is no slouch.

Yeah, it'll look ugly! But if you're lucky it'll still work fine. And now you have a war story that you can tell the kids, and the newbies here on CN! Plus you've had the worst thing you could ever imagine happening to your scope happen... and you lived to tell the tale! So has the scope.

I recall a story about a guy who, when he bought a new guitar, the first thing he would do would be to open the case, and drop his keys on it! When asked why he did such a thing, he replied that it was so he wouldn't have to continue worrying about when the first scratch would happen. He figured that by doing it himself, he got it out of the way, and was then able to just enjoy the guitar!

Good luck.


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aatt
sage


Reged: 07/26/12

Loc: CT
Re: Depressed-accident with my new mirror new [Re: mayidunk]
      #5526766 - 11/18/12 08:18 PM

Thanks-I will have to try the paint thing out. You are right-this mirror is no slouch my first star test was textbook. That makes this all the more upsetting.

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dan_h
Carpal Tunnel


Reged: 12/10/07

Re: Depressed-accident with my new mirror new [Re: aatt]
      #5526767 - 11/18/12 08:18 PM

Sorry to hear of your misfortune. I too have done some things that left me feeling totally depressed and I was not the first.

If you don't want to paint the damaged spot in the glass, you could cut a small circle of peel and stick flocking material and just cover it it up. Ugly in daylight but effective at preventing light scatter and easy enough to remove if ever needed.

good luck,

dan


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panhard
It's All Good
*****

Reged: 01/20/08

Loc: Markham Ontario Canada
Re: Depressed-accident with my new mirror new [Re: dan_h]
      #5526889 - 11/18/12 09:24 PM

I say use it on a good night before you do anything to the mirror.

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Mike B
Starstruck
*****

Reged: 04/06/05

Loc: shake, rattle, & roll, CA
Re: Depressed-accident with my new mirror new [Re: panhard]
      #5527095 - 11/18/12 11:50 PM

Yes, a bummer fersure! Had a few minor boofs myself, a few scratches on my primary (coatings only, not into glass) resulted. But have found the views are entirely unaffected. Likely yours will be, also.

Since then, i no longer feel the urge to offer gravity free-shots at my mirror! I've even heard of folks tying a thread around their tools & looping it over their wrist while adjusting collimation, etc., to prevent accidental drops.

Let us know how views turn out the next steady night! And always remember- if the good folks from MacDonald Observatory should come by for a look, make sure they keep their safeties on!


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mayidunk
Don't Ask...
*****

Reged: 02/17/10

Loc: Betwixt & Between...
Re: Depressed-accident with my new mirror new [Re: aatt]
      #5527122 - 11/19/12 12:07 AM

Practically speaking, unless the pin hit it in such a way as to cause a crack to form (a pretty remote chance), you'll soon be glued to the eyepiece once again.

Where do you go for a dark sky site?


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Binojunky
Carpal Tunnel
*****

Reged: 12/25/10

Re: Depressed-accident with my new mirror new [Re: mayidunk]
      #5527538 - 11/19/12 09:25 AM

Its like the new car and waiting for the first stone chip or shopping cart dent, I remember years back getting a 10" Meade dob and the first night out dripping coffee on to the sonotube and staining the white paint, recently I bought a high end expensive watch, within a week I,d managed to put a couple of scuffs on the bracelet, the mirror damage is what it is, its done and you can,t turn back the clock however don,t let it eat you up, go out and enjoy the scope, sorry to here about your accident,DA.

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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Depressed-accident with my new mirror new [Re: Binojunky]
      #5527624 - 11/19/12 10:21 AM

Don't feel bad. First Light with my 10XTi about a year ago: I was carring the OTA to the mount; I had picked it up by the two ends. The front cover came off and the Secondary end of the scope took a nose dive to the dirt (luckily there was some grass there). Also, luckily, my collimation wasn't off, a slight tweek to the primary, and off I went....still dreading my first mirror ding. I've already had to blow off a couple of mosquitos. Now when I store the scope in the shed, I put it horizontially.

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killdabuddha
Pooh-Bah
*****

Reged: 08/26/11

Re: Depressed-accident with my new mirror new [Re: Binojunky]
      #5527633 - 11/19/12 10:27 AM

I can't find the link, but there was a guy who posted his ordeal at his blog...He was usin large magnets as counterweights when, a little too close to horizon, one came unstuck and bounced off his new Zambuto mirror. He sent it to Carl for examination and about a quarter-sized spot had stress-fractured beneath the coating, makin that bit unusable. Carl's advice to him was to just cover that spot, as others here have suggested. The amount of light loss was negligible.

As for cars, I always put an extra ding in the fender before someone else does. First got the idea from Sheldon Vanauken's "A Severe Mercy."

A cruce salus. Absit invidia.


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Depressed-accident with my new mirror new [Re: killdabuddha]
      #5528150 - 11/19/12 03:07 PM

I dropped a 2.5 lb counterweight on the mirror of my Discovery many years ago. It fell from the height of the top of the UTA!
It landed flat (fortune smiles on the idiot) and didn't bounce, and it hit hard enough to slightly flatten the edges of the counterweight.
It left two scuff marks in the coating, with no obviously fractures leading away from the scuff marks (lucky, I know), about 12mm x 1-2mm wide. I was going to paint them black, then decided to test the mirror to see if those marks were visible either in the out-of-focus star image or in-focus as scattered light.
Nope. No effect on anything except my ego for having been so stupid, stupid, stupid
We worry a lot about such things, but the truth is that such minor scratches and scuff marks are really not very important.
If your marks are larger and you CAN see them in the out-of-focus star image, just paint them in with flat black paint and ignore them. [I know, it's hard.....]


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frito
Pooh-Bah


Reged: 10/05/12

Loc: Fremont, CA
Re: Depressed-accident with my new mirror new [Re: Starman1]
      #5528197 - 11/19/12 03:29 PM

I feel your pain. Last Friday I was installing a bracket for my new finder scope and dropped the steel reinforcement plate on my XT8 mirror. My heart sank but the only damage was a small maybe 1/8th inch diameter surface chip and so far it looks like I won't even need to black the spot out

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Mike B
Starstruck
*****

Reged: 04/06/05

Loc: shake, rattle, & roll, CA
Re: Depressed-accident with my new mirror new [Re: frito]
      #5528238 - 11/19/12 03:43 PM

Gravity is a harsh & unforgiving master! It neither takes account of kings, nor suffers fools with tools (like me).
Our Dob's may be optical configurations first, but are secondarily anti-gravity devices.


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csrlice12
Postmaster
*****

Reged: 05/22/12

Loc: Denver, CO
Re: Depressed-accident with my new mirror new [Re: Mike B]
      #5528263 - 11/19/12 03:53 PM

"Gravity is a harsh & unforgiving master!"



Edited by David Pavlich (11/19/12 10:05 PM)


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dvb
different Syndrome.
*****

Reged: 06/18/05

Loc: Vancouver, Canada
Re: Depressed-accident with my new mirror new [Re: csrlice12]
      #5528388 - 11/19/12 04:53 PM

I try to never do any maintenance on my scope - including collimation - unless the tube is horizontal

But that isn't always possible, and I've had a few "D'Oh"! moments myself.


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frito
Pooh-Bah


Reged: 10/05/12

Loc: Fremont, CA
Re: Depressed-accident with my new mirror new [Re: dvb]
      #5528419 - 11/19/12 05:15 PM

Quote:

I try to never do any maintenance on my scope - including collimation - unless the tube is horizontal

But that isn't always possible, and I've had a few "D'Oh"! moments myself.




Yeah i do the same thing normally and when i was removing the old finder mounting bracket i did so horizontally. the problem was putting the new one back in with the reinforcement bracket was proving to be hard in that position and i didn't want to drop it onto the secondary it was right above so i thought hmm ill do it with the scope vertical and gravity will hold it in place till i get the first nut on and it did the first time i put it on. then i realized i put it on backwards and it all went downhill from there


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Mike B
Starstruck
*****

Reged: 04/06/05

Loc: shake, rattle, & roll, CA
Re: Depressed-accident with my new mirror new [Re: frito]
      #5528430 - 11/19/12 05:22 PM

Quote:

...and it all went downhill from there




Ayup, gravity will do that.


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