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So my antireflective coating is damaged

cassegrain catadioptric Celestron optics beginner
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#1 StargazerPrivateer

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Posted 03 August 2020 - 11:54 PM

So I bought a used Celestron C6 and there was a massive foggy layer on the inside of it, most likely mold and I cleaned it with a microfiber cloth and lens solution. I am a beginner (probably wasn't the best idea to get a C6) The previous owner kept it in the basement for a while I think. All the foggy stuff came off then I noticed that in some areas the antireflective coating is damaged/missing. But only on the inside of the collector plate, thankfully not both sides. I get pretty massive chromatic aberration off of planets and anything I look at (just cannot focus it perfectly) I attached a photo of the aberration, I was playing around with the settings and lenses, tried the barlow, an apochromatic wide field lens, the eyepiece it came with and they all still show the chromatic aberration. 

 

I did clean it and I most likely rubbed too hard in some sections so it came off, or the mold already ate into it, I have no idea which it was or a mix of both but I'm pretty bummed right now and I really don't know the best course of action. Will collimating it decrease the chromatic aberration? Should I call celestron and ask how much to re-coat it? I found another private company that advertises doing it: https://www.majestic...pe-coating.html

 

I am going to call them tomorrow for a quote as well. I also attached a picture of Saturn using my phone to the eyepiece, it looks slightly better in person but only a bit. 

 

It was a beginner mistake to even buy the scope but I don't know what to do now if anyone can help I'd greatly appreciate it thank you

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Edited by StargazerPrivateer, 03 August 2020 - 11:58 PM.


#2 chronos1701

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Posted 04 August 2020 - 12:10 AM

Not sure about the coatings, but the image of Saturn looks like atmospheric diffraction you'll normally get when the object is too low on the horizon. The blue side faces the zenith and the red side is toward the horizon.


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#3 StargazerPrivateer

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Posted 04 August 2020 - 12:21 AM

Not sure about the coatings, but the image of Saturn looks like atmospheric diffraction you'll normally get when the object is too low on the horizon. The blue side faces the zenith and the red side is toward the horizon.

You are correct, it was I think about 30-35 degrees from the horizon



#4 Traveler

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Posted 04 August 2020 - 12:42 AM

Did you remove the corrector plate and mounted the plate exactly the same back?

 

...And a warm welcome to Cloudynights of course. Glad you join us!


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#5 sg6

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Posted 04 August 2020 - 01:50 AM

I would worry about it. What is on the corrector is kind of minimal. Having seen a few I expecy it is a single layer and so the difference in light transmission should be 96% at the lost areas and 98% at the still good areas.

 

As the corrector is where it is then that will have close to zero optical effect oddly.

 

I would have said that what you need is for any crud/dirt whatever to be removed if not already. Mainly so the incoming light has no actual particals in the way. Then get out and use it.

 

Chromatic aberration is not caused by the anti reflection coating, that is something alse and would agree with others atmosphere. You will eventually realise that an atmosphere is maybe good for breathing but not good for astronomy. And at times not always good for the breathing bit either.

 

With Travelers comments did you know about the orientation of the corrector or not? Would assume not. Will also say I am unsure if it is significant. Mass production and making an alignmnet mark don't go together in my mind.

 

If and only if you feel like it the corrector may have a small (often very small and well hidden) mark on it that people say has to be either at some clock position or aligned with another well hidden mark. So you might decide it is worth removing the corrector again and searching for the 2 (or 1) marks and just reassembling it with the supposid correct positioning/alignment.

 

Would also give you the opertunity to gently clean the rear a bit more again if you wanted. Do not get bothered about the AR coating loss. Just avoid the shiny silvered bit - that you do not want to damage.

 

After that identify a few targets and get viewing. But you will not see any difference with or without the full AR coating.

 

There is a lot of panic about anything optical, but glass etc is actually a very robust material. Ever stood on one of the glass inserts in a sky needle thing? They are not actually that thick.


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#6 StargazerPrivateer

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Posted 04 August 2020 - 08:58 AM

Did you remove the corrector plate and mounted the plate exactly the same back?

...And a warm welcome to Cloudynights of course. Glad you join us!


Yes I did thank you for the welcome
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#7 StargazerPrivateer

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Posted 04 August 2020 - 09:05 AM

I would worry about it. What is on the corrector is kind of minimal. Having seen a few I expecy it is a single layer and so the difference in light transmission should be 96% at the lost areas and 98% at the still good areas.

As the corrector is where it is then that will have close to zero optical effect oddly.

I would have said that what you need is for any crud/dirt whatever to be removed if not already. Mainly so the incoming light has no actual particals in the way. Then get out and use it.

Chromatic aberration is not caused by the anti reflection coating, that is something alse and would agree with others atmosphere. You will eventually realise that an atmosphere is maybe good for breathing but not good for astronomy. And at times not always good for the breathing bit either.

With Travelers comments did you know about the orientation of the corrector or not? Would assume not. Will also say I am unsure if it is significant. Mass production and making an alignmnet mark don't go together in my mind.

If and only if you feel like it the corrector may have a small (often very small and well hidden) mark on it that people say has to be either at some clock position or aligned with another well hidden mark. So you might decide it is worth removing the corrector again and searching for the 2 (or 1) marks and just reassembling it with the supposid correct positioning/alignment.

Would also give you the opertunity to gently clean the rear a bit more again if you wanted. Do not get bothered about the AR coating loss. Just avoid the shiny silvered bit - that you do not want to damage.

After that identify a few targets and get viewing. But you will not see any difference with or without the full AR coating.

There is a lot of panic about anything optical, but glass etc is actually a very robust material. Ever stood on one of the glass inserts in a sky needle thing? They are not actually that thick.


Thank you that seems to be the consensus, I got worried the antireflective coating would be causing the chromatic aberration but thats atmosphere that makes more sense.

Do they make aspheric telescopes to reduce chromatic aberration?

And yes I put it back exactly same position. Some of the cork things fell out when I was trying to put it back on but then I glued them on the sides so they wouldn't fall out, I think in the same positions. But the rotation is definitely the same.

Thank you for all your insights

#8 Michael Covington

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Posted 04 August 2020 - 09:09 AM

Schmidt-cassegrain telescopes have virtually zero chromatic aberration.   The air in front of you on the other hand can cause chromatic dispersion.

In the 1970s, Celestrons did not have antireflective coating on the correctors at all.  They figured that it was so few surfaces as to be hardly worth the trouble.
 


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#9 RichA

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Posted 04 August 2020 - 10:13 AM

Losing some coating won't have any observable impact on the scope as it takes at least an 8-10% light-loss to really begin to see it and coatings only improve throughput 2.5% per surface, plus all the coating would have to be removed. 



#10 KTAZ

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Posted 04 August 2020 - 10:27 AM

As we seem to have consensus that atmosphere is your issue, and I also support that, you should next look to collimation. It is pretty likely that a scope that has been mis-cared for has never even been checked. Do some reading on collimation and give that a whirl. You may see some nice results.

 

BTW, please don't use lens cleaner to clean your corrector or mirrors. There are many "how-to's" posted here on CN, but the fact is that any marketed brand of lens cleaner will leave residue. Use a mixture of distilled water and 99% isopropyl alcohol, perhaps 3 to 1. I prefer sheet sterile cotton torn to size over any brand of kleenex.


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#11 sunrag

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Posted 04 August 2020 - 05:36 PM

It is most likely due to mis-aligned corrector plate. I don’t think AR coatings loss should cause more CA (i had a refractor with AR coating gone in huge patches but that did not increase CA at all).

In general i have found that any cleaning solution i use leaves streaks or haze (IPA, Distilled water, Zeiss, Photo-flo, whatever). So I don’t trust any of them. On my last attempt, i used steam from a boiling cup of water to mist the corrector plate very lightly, then wiped it off with Kleenex. So far this had the least haze or streaking.

#12 SeattleScott

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Posted 04 August 2020 - 06:40 PM

The concerning image is the 3rd one. What is that a picture of? Very strong red/blue shift but it looks like you are looking at something close up like tree bark or a fence, which would rule out atmospheric dispersion.

You say you can’t get sharp focus on anything you look at. Atmospheric dispersion would only impact targets low in the sky, unless you are stargazing on the US East Coast right now.

The fog is a bit of a mystery but most attribute it to degassing of materials used to make the scope. Seems to be more or less unique to Celestron. Often it fogs back up in a couple years so cleaning the inside of the corrector can become more or less routine maintenance with a Celestron. I get the impression regular use can help as the air inside gets a little bit of opportunity to circulate.

Scott

Edited by SeattleScott, 04 August 2020 - 06:48 PM.


#13 StargazerPrivateer

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Posted 04 August 2020 - 11:18 PM

I did some collimation and the images definitely look better now. This is an unprocessed picture of jupiter from putting my cell phone to the eyepiece. Thank you all for taking the worry out of me smile.gif

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Edited by StargazerPrivateer, 04 August 2020 - 11:18 PM.

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#14 Nippon

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Posted 05 August 2020 - 08:19 AM

As Michael Covington pointed out Celestron didn't even coat the corrector back in the 70s. I have a Dall Kirkham reflector and there is not a single refractive element until the light cone gets to the eyepiece and it will show red and blue on Jupiter and Saturn when they are still low. As a matter of fact right now they are so low still at their highest point that on some nights they  have the red and blue fringe all night.


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#15 Eddgie

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Posted 05 August 2020 - 08:54 AM

While I agree that the coating damage will have little consequence, the real issue I see here is that the coating came off.

 

Normally, to get these coatings off, they have to be literally polished off of the surface.  If you were able to rub it off, that means that it was not properly applied to start with. 

 

Now I can't tell much from the picture, but if the coatings really did come off of the glass, shame on Celestron. That should never happen if the coatings are properly applied. Any coating that can simply be rubbed of that easily is a defective coating. 

 

The other thing is what was on the rear of the corrector was possibly the same outgassing that was hitting the EdgeHDs seven or eight years ago.. This was a Celestron screwup for sure. I had owned many Celestrons prior to the EdgeHD 8" and never experienced this issue, but my Edge 8 got the greasy film on the corrector and it had to be pulled and cleaned.  Since I had the first EdgeHD sold in the US (that I know of), I was the first to experience and report the problem and thought maybe it was just an anomaly, but soon after, others started having the issue as well.  This is the first I have heard of it for the C6, but the C6 has been plagued by baffle reflections and this problem my still be occurring. 

 

Recently I saw a post were someone with a new EdgeHD was asking how many defects they should expect with pictures of the defects on his scope.   ReallyREALLY???

 

As others said, this will have minimal effect on the view, but it is alarming that this would happen at all. 


Edited by Eddgie, 05 August 2020 - 08:55 AM.

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#16 StargazerPrivateer

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Posted 05 August 2020 - 10:53 AM

While I agree that the coating damage will have little consequence, the real issue I see here is that the coating came off.

 

Normally, to get these coatings off, they have to be literally polished off of the surface.  If you were able to rub it off, that means that it was not properly applied to start with. 

 

Now I can't tell much from the picture, but if the coatings really did come off of the glass, shame on Celestron. That should never happen if the coatings are properly applied. Any coating that can simply be rubbed of that easily is a defective coating. 

 

The other thing is what was on the rear of the corrector was possibly the same outgassing that was hitting the EdgeHDs seven or eight years ago.. This was a Celestron screwup for sure. I had owned many Celestrons prior to the EdgeHD 8" and never experienced this issue, but my Edge 8 got the greasy film on the corrector and it had to be pulled and cleaned.  Since I had the first EdgeHD sold in the US (that I know of), I was the first to experience and report the problem and thought maybe it was just an anomaly, but soon after, others started having the issue as well.  This is the first I have heard of it for the C6, but the C6 has been plagued by baffle reflections and this problem my still be occurring. 

 

Recently I saw a post were someone with a new EdgeHD was asking how many defects they should expect with pictures of the defects on his scope.   ReallyREALLY???

 

As others said, this will have minimal effect on the view, but it is alarming that this would happen at all. 

To be fair, because of the mold I did rub quite hard and I saw a white reflective area that I thought was further mold so I rubbed even harder and the area just got bigger so I stopped. I used a microfiber cloth with lens cleaner, I really did put quite some force into it. The telescope is from 1997 if that gives you more info



#17 Nippon

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Posted 05 August 2020 - 11:11 AM

While I agree that the coating damage will have little consequence, the real issue I see here is that the coating came off.

 

Normally, to get these coatings off, they have to be literally polished off of the surface.  If you were able to rub it off, that means that it was not properly applied to start with. 

 

Now I can't tell much from the picture, but if the coatings really did come off of the glass, shame on Celestron. That should never happen if the coatings are properly applied. Any coating that can simply be rubbed of that easily is a defective coating. 

 

The other thing is what was on the rear of the corrector was possibly the same outgassing that was hitting the EdgeHDs seven or eight years ago.. This was a Celestron screwup for sure. I had owned many Celestrons prior to the EdgeHD 8" and never experienced this issue, but my Edge 8 got the greasy film on the corrector and it had to be pulled and cleaned.  Since I had the first EdgeHD sold in the US (that I know of), I was the first to experience and report the problem and thought maybe it was just an anomaly, but soon after, others started having the issue as well.  This is the first I have heard of it for the C6, but the C6 has been plagued by baffle reflections and this problem my still be occurring. 

 

Recently I saw a post were someone with a new EdgeHD was asking how many defects they should expect with pictures of the defects on his scope.   ReallyREALLY???

 

As others said, this will have minimal effect on the view, but it is alarming that this would happen at all. 

I sent my Edge 8 in for outgassing that happened in the first year and they covered it under warranty. I recently sold the scope and it never did it again in about 4 more years that I owned it. I had a 28mm Edmund Plossl that came with one of the last of the Edmund Astroscans and the coating rubbed off the first time I cleaned it. Definitely a defective coating job.


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#18 Eddgie

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Posted 05 August 2020 - 11:31 AM

To be fair, because of the mold I did rub quite hard and I saw a white reflective area that I thought was further mold so I rubbed even harder and the area just got bigger so I stopped. I used a microfiber cloth with lens cleaner, I really did put quite some force into it. The telescope is from 1997 if that gives you more info

While it might be possible for mold to etch the coating, I still think it is unlikely that it could be that easily removed, but if you say you used excessive pressure, then yeah, possibly that you did remove it, but if it was properly applied, this should be very hard to do. But if you are saying your method was so agressive that you think it could have removed the coating, well the only thing I can say is "Ouch."


Edited by Eddgie, 05 August 2020 - 11:31 AM.

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#19 Nippon

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Posted 05 August 2020 - 12:25 PM

My understanding is that modern coatings become part of the glass and the optic must refigured to remove it. In other words ground off. Edggie you may know if this is true but I read that the glass used in the early days of refractors would tarnish over a long period of time and it was discovered that these tarnished lenses had better transmission and contrast than new lenses. Truth or urban myth?


Edited by Nippon, 05 August 2020 - 12:26 PM.



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