Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Nicked Primary — Disaster — Edge 9.25

  • Please log in to reply
24 replies to this topic

#1 The Cat

The Cat

    Mariner 2

  • -----
  • topic starter
  • Posts: 264
  • Joined: 02 Jun 2007

Posted 13 August 2022 - 02:50 PM

All —

 

Disaster.  I bought a new set of Bob’s Knobs to replace a defective set that had allowed for terrible Collimation. In an effort to check whether the secondary mirror was level, I unscrewed the Faststar plate on the outside of the corrector plate.  Thus far, great.  I studied the mirror from the side and it was bulging out way too much on one side.  It took me a while, messing with the knobs, to get the mirror level.  But I got it level.

 

when I tried to screw the outer Fastar component to the inside component (female component, I guess) the inside component detached from the corrector plate. In an effort to see what had happened  I rotated the telescope on the mount.  I lost control and the interior part of the faststar unit rolled down the tube and hit the mirror. 
 

i think it nicked the primary  mirror.  Could you please look at the middle photo below and let me know what I should do next.  Ask Celestron to install a new primary? But a new Edge?

 

In order to fix the Fastar components, I had to remove the corrector plate to screw the Fastar components together.  I think I did that job correctly. But there are blemishes on the corrector plate now. 
 

I’m using the term Fastar because that is what is written on the unit.  I’m talking about the housing for the secondary mirror, half of which is on the outside of the corrector plate, facing the sky. The other part of the housing is on the inside of the corrector plate.

 

Sigh — all just an effort to collimate.  I really had to remove the secondary though.  The mirror was so out of whack that I would not have been able to see an airy disc. 
 

thanks!

 

felix 

 

Attached Thumbnails

  • 97ABA13F-21B4-4612-AAED-967F71B3FE05.jpeg
  • 7A422F5C-1C59-408B-B288-F8AEBA87DEFB.jpeg


#2 John Miele

John Miele

    Fly Me to the Moon

  • *****
  • Posts: 5,501
  • Joined: 29 May 2005
  • Loc: North Alabama

Posted 13 August 2022 - 03:08 PM

Kind of hard to tell with that but probably have no affect at all. I would just try to enjoy the scope and let the painful memory fade with time!


  • Jon Isaacs, RedLionNJ, Raginar and 3 others like this

#3 jlinsobe

jlinsobe

    Ranger 4

  • *****
  • Posts: 321
  • Joined: 20 Dec 2021
  • Loc: South Florida

Posted 13 August 2022 - 03:15 PM

Personally, I would send it to Celestron, and see what they can do.
Just to ensure that everything is within their own specs and tolerances.

They may be able to fix that nick, they may have to replace it.  

Unfortunately, new units have a significant delivery backlog.  



#4 photomagica

photomagica

    Viking 1

  • *****
  • Posts: 643
  • Joined: 23 Jun 2013
  • Loc: Calgary and Tucson

Posted 13 August 2022 - 03:17 PM

Do nothing. This will have zero effect on performance. Just collimate and forget it happened.

Bill


  • Jon Isaacs, Jeff B, Traveler and 17 others like this

#5 astrochoker1

astrochoker1

    Lift Off

  • -----
  • Posts: 24
  • Joined: 14 Oct 2010
  • Loc: Tucson, Arizona

Posted 13 August 2022 - 03:24 PM

I agree with Viking  1. This will have little impact on your image.

Heck, there's telescopes with primary mirrors that have bullet holes in them that work just fine.



#6 Jon Isaacs

Jon Isaacs

    ISS

  • *****
  • Posts: 102,273
  • Joined: 16 Jun 2004
  • Loc: San Diego and Boulevard, CA

Posted 13 August 2022 - 03:38 PM

Kind of hard to tell with that but probably have no affect at all. I would just try to enjoy the scope and let the painful memory fade with time!

 

Do nothing. This will have zero effect on performance. Just collimate and forget it happened.

Bill

 

It looks bad, it's a bad memory but it's a tiny defect and has an effect on the image approximately proportional to its area. Compare it's size to the size of the central obstruction to estimate it's effect..

 

An bad memory, the scope is no longer pristine and perfect, in reality, telescopes never are. 

 

Enjoy the scope..

 

Jon


  • Jeff B, AhBok, BFaucett and 6 others like this

#7 M11Mike

M11Mike

    Apollo

  • *****
  • Posts: 1,129
  • Joined: 02 Apr 2016
  • Loc: Ballston Lake, NY

Posted 13 August 2022 - 03:39 PM

Nick is so small will have virtually NO impact as to the primary's performance --- as long as you have everything all set with the secondary and  can now collimate it properly --- you now have a scope with some "character".  :-)   (and a "story" to tell) 

 

Clear skies..... 


  • RedLionNJ, AhBok, BFaucett and 4 others like this

#8 KTAZ

KTAZ

    Gemini

  • *****
  • Posts: 3,191
  • Joined: 09 Apr 2020
  • Loc: Scottsdale, AZ

Posted 13 August 2022 - 03:46 PM

Agree with all others...if that was a dust bunny or a fleck of WHATEVER, most of us would not even bother pulling the corrector to get it off.


  • Jon Isaacs and 12BH7 like this

#9 WadeH237

WadeH237

    Cosmos

  • *****
  • Moderators
  • Posts: 8,794
  • Joined: 24 Feb 2007
  • Loc: Ellensburg, WA

Posted 13 August 2022 - 03:48 PM

The experience was awful, but the damage is not a big deal.

 

As others have mentioned, it is unlikely that it will affect your images at all.  If it does have an effect, it will be some kind of diffraction thing.  If that happens, just black it out.  Touching it with a black Sharpie might be enough.  In the worst case, you might need just a dab of flat black paint.  At that point, it will have no discernible effect whatsoever.


  • RedLionNJ, BFaucett and 12BH7 like this

#10 SgrB2

SgrB2

    Surveyor 1

  • -----
  • Posts: 1,864
  • Joined: 10 Sep 2007
  • Loc: Ellicott City, MD

Posted 13 August 2022 - 03:57 PM

Kind of hard to tell with that but probably have no affect at all. I would just try to enjoy the scope and let the painful memory fade with time!

 Ditto!  Read this:

 

https://www.nytimes....irror-by-7.html


  • Toups and BFaucett like this

#11 CHASLX200

CHASLX200

    ISS

  • *****
  • Posts: 28,036
  • Joined: 29 Sep 2007
  • Loc: Tampa area Florida

Posted 13 August 2022 - 04:52 PM

It looks bad, it's a bad memory but it's a tiny defect and has an effect on the image approximately proportional to its area. Compare it's size to the size of the central obstruction to estimate it's effect..

 

An bad memory, the scope is no longer pristine and perfect, in reality, telescopes never are. 

 

Enjoy the scope..

 

Jon

Maybe use a Q tip with a dab of flat black paint.


  • rhaskins likes this

#12 AhBok

AhBok

    Soyuz

  • *****
  • Posts: 3,515
  • Joined: 02 Dec 2010
  • Loc: Lakeland, TN

Posted 13 August 2022 - 06:39 PM

Yep. Drop two bucks in a “swear jar” and move on. Keep the jar. You’ll need it again!
  • GoFish and 12BH7 like this

#13 PETER DREW

PETER DREW

    Surveyor 1

  • *****
  • Posts: 1,869
  • Joined: 31 May 2017

Posted 13 August 2022 - 06:51 PM

The only detrimental affect would be it's resale value.


  • C0rs4ir_ likes this

#14 The Cat

The Cat

    Mariner 2

  • -----
  • topic starter
  • Posts: 264
  • Joined: 02 Jun 2007

Posted 13 August 2022 - 07:05 PM

Thank you for all the reassurances! I’m surprised to hear that the problem is not more serious.

I think that the Collimation got so far out of wack because one of the Bob’s knobs wasn’t turning. As a result, I kept mucking around with the other two knobs in an effort to collimate and it threw the mirror further and further off level. But we’ll see, as I collimate over the next few sessions, whether the mirror remains in place.
  • BFaucett likes this

#15 BFaucett

BFaucett

    Mercury-Atlas

  • *****
  • Posts: 2,858
  • Joined: 12 Jul 2014
  • Loc: Houston, Texas 29.78° N

Posted 13 August 2022 - 08:28 PM

 Ditto!  Read this:

 

https://www.nytimes....irror-by-7.html

 

Yep. Another source and a photo:

 

 

The McDonald gun shooting incident
MARCH 26, 2015

https://astroanecdot...oting-incident/

 

 

McDonald 107 inch.jpg

 

The primary mirror of the 2.7m (107 inch) telescope at McDonald Observatory. The bullet holes can clearly be seen.

Photo credit: McDonald Observatory.

source: https://astroanecdot...oting-incident/

 

 

the-harlan-j-smith-telescope.jpg

 

 

From Wikipedia:

 

The Harlan J. Smith Telescope is a 107-inch (2.7 m) telescope located at the McDonald Observatory, in Texas, in the United States. This telescope is one of several research telescopes that are part of the University of Texas at Austin observatory perched on Mount Locke in the Davis Mountains of west Texas.

 

The holes effectively reduced the 107-inch (2.7 m) telescope to the equivalent of a 106-inch telescope (or about 2.5 centimeters less), but did not affect the quality of the telescope's images, only the amount of light it can collect.

https://en.wikipedia...Smith_Telescope

 

(I added the bold emphasis.) 

 

Cheers! Bob F. smile.gif


  • Toups likes this

#16 GoFish

GoFish

    Soyuz

  • *****
  • Posts: 3,657
  • Joined: 30 Nov 2016
  • Loc: Wisconsin

Posted 13 August 2022 - 08:30 PM

In the unlikely event you need to black out the tiny “ding” I would use a black Sharpie. Isopropyl alcohol will remove Sharpie ink, in my experience, and won’t bother the coatings. You know, just in case something goes wrong with the paint job …. lol.gif


  • BFaucett likes this

#17 KTAZ

KTAZ

    Gemini

  • *****
  • Posts: 3,191
  • Joined: 09 Apr 2020
  • Loc: Scottsdale, AZ

Posted 13 August 2022 - 09:26 PM

Thank you for all the reassurances! I’m surprised to hear that the problem is not more serious.

I think that the Collimation got so far out of wack because one of the Bob’s knobs wasn’t turning. As a result, I kept mucking around with the other two knobs in an effort to collimate and it threw the mirror further and further off level. But we’ll see, as I collimate over the next few sessions, whether the mirror remains in place.

Ok, now I gotta get on my soapbox...

 

I don't like Bob's knobs. They just don't give you enough grip to get reasonable torque on those screws. Use Allen head screws and a t-handle wrench.


  • tturtle and Cpk133 like this

#18 rhaskins

rhaskins

    Viking 1

  • *****
  • Posts: 747
  • Joined: 07 Sep 2015
  • Loc: Minnesota

Posted 14 August 2022 - 09:34 AM

First, no significant damage from your picture.

 

Second, next time you do something like that remove the secondary and replace the screws when it is out of the corrector and not over the large expensive mirror.

 

Third, a lot of folks do not like bob's knobs because of incidents like yours. Like stated above, I replaced screws on the secondary with plain socket head cap screws so I use an allen wrench to adjust. My C8 scope had, I believe, #6-32 threads so I got an assortment of screws to find the correct length. IDK if your scope has #6-32 so you need to check. Once in place, LITTLE little adjustments to get collimation. If you have a Hotech it is easy for initial collimation.

 

Screw assortment: https://www.amazon.c...product_details

 

And that little owwwie can be dabbed with some Krylon ultra flat black spray paint #1602 and it will never reflect stray light again. I don't know where you can get that stuff but Filmtools has it.

 

I have an old C8 I am working on right now with a 1/2 inch to 3/4 inch divot on the side of the mirror. I got it to collimate easy enough and the divot, in my estimation, will not really cause a problem. THAT scope has divot, rust and focuser issues so it a while before it will see its new first light.

 

Rick


  • tturtle likes this

#19 Jeff B

Jeff B

    Cosmos

  • *****
  • Posts: 8,654
  • Joined: 30 Dec 2006

Posted 14 August 2022 - 10:35 AM

As Yuri once told me concerning three small scratches, "You will never see them from the eyepiece end of the telescope.  You will only see them from the front.  Stop looking from the front."  And he's absolutely correct.

 

The real problem is the effect on any resale price and just how crazy picky some folks can be about cosmetic issues, especially when it comes to the glass & coatings.    

 

Sorry for this condition, but please stop looking from the front is my advice.

 

Jeff


  • Toups, CeeKay and Lumix.guy like this

#20 tturtle

tturtle

    Ranger 4

  • *****
  • Posts: 364
  • Joined: 03 Mar 2009
  • Loc: Florida

Posted 14 August 2022 - 10:47 AM

Good for you for having the courage to try and correct the secondary alignment problem yourself. The tiny nick on the primary mirror will not have a discernible effect on the optics, although as others have noted you may want to blacken it with a dot of black paint if you decide to remove the corrector. I mention that as you said there are some blemishes on the corrector so at some point you may want to remove it for cleaning. My advise is to go ahead with the collimation and enjoy the scope for a while before a second attempt at any disassembly.  Also, you are now one of our CN resident experts on SCT disassembly! Yah!



#21 firemachine69

firemachine69

    Apollo

  • *****
  • Posts: 1,370
  • Joined: 19 May 2021

Posted 14 August 2022 - 11:21 AM

The odds of you landing a star on that exact area of the corrector plate, on a regular or even occasional basis, is just about zero. You've definitely lost some resale value there, and do take extra care when travelling with it (think a stone chip in your windshield that becomes a crack over time from the bumps on the road), but no, don't worry about performance.

 

 

As well, a speck of dust on the eyepiece end tends to show up, because the point of light is concentrated. Whereas the light at the corrector plate is "bulk" lighting. I've got a tiny 1/4" nick in the coatings of my Evolution HD, and I actually have spent a whole evening trying to get it to interfere with the eyepiece view, and have come away completely unsuccessful.


Edited by firemachine69, 14 August 2022 - 11:23 AM.


#22 Cpk133

Cpk133

    Vanguard

  • -----
  • Posts: 2,159
  • Joined: 14 Mar 2015
  • Loc: SE Michigan

Posted 14 August 2022 - 12:30 PM

The odds of you landing a star on that exact area of the corrector plate, on a regular or even occasional basis, is just about zero. You've definitely lost some resale value there, and do take extra care when travelling with it (think a stone chip in your windshield that becomes a crack over time from the bumps on the road), but no, don't worry about performance.

 

 

As well, a speck of dust on the eyepiece end tends to show up, because the point of light is concentrated. Whereas the light at the corrector plate is "bulk" lighting. I've got a tiny 1/4" nick in the coatings of my Evolution HD, and I actually have spent a whole evening trying to get it to interfere with the eyepiece view, and have come away completely unsuccessful.

Light from a star arrives as a plane wave so the chances of it interacting are 100%.  Its not like a ray trace where the star has to be perfectly aligned with a spec of dust or damage to have an effect.  If the star is in the field of view, its light is passing through the whole corrector at the same time.  The first star you looked at would have revealed any effect from your coating issue, no need to align anything or spend a whole night looking shocked.gif.


Edited by Cpk133, 14 August 2022 - 12:36 PM.

  • RedLionNJ and AhBok like this

#23 RedLionNJ

RedLionNJ

    Fly Me to the Moon

  • *****
  • Moderators
  • Posts: 5,949
  • Joined: 29 Dec 2009
  • Loc: Red Lion, NJ, USA

Posted 14 August 2022 - 01:35 PM

Let's say the surface of your primary is around 60 square inches (it may be a tad larger, in fact), as an approximation.  That ding is what, a quarter inch across? About 0.05 square inches?

 

So the ding has reduced your effective mirror surface by about 0.08%.  I wouldn't be overly-concerned.



#24 gnowellsct

gnowellsct

    ISS

  • *****
  • Posts: 21,640
  • Joined: 24 Jun 2009

Posted 14 August 2022 - 05:32 PM

Ok, now I gotta get on my soapbox...

I don't like Bob's knobs. They just don't give you enough grip to get reasonable torque on those screws. Use Allen head screws and a t-handle wrench.


I agree, even though both of my scts have Bob's knobs. But they've been there for decades and so why mess with success.

In recent times I've seen that rod mollise has also recommended that the game is not worth the candle as far as Bob's knobs go.

Another advantage of Allen head screws is they give you very precise control whereas when you grab a Bob's knob with your index finger and thumb not so much. This is especially true as it gets tighter.

#25 gnowellsct

gnowellsct

    ISS

  • *****
  • Posts: 21,640
  • Joined: 24 Jun 2009

Posted 14 August 2022 - 05:34 PM

You know in other parts of our hobby these kinds of things occasionally occur. There are a fair number of primary mirror accidents that happened with newtonians. And here and there are you even see a refractor that has a crack in one of the lenses.

There is an impact if you ever try to resell the telescope.

Greg N


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics