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Uh-oh, how bad is my lens?

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13 replies to this topic

#1 bicyclemonkey

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Posted 16 September 2020 - 10:56 AM

I received the scope and it had what looked like a scratch on the lens from what I'm guessing was poor packing.  There had been plastic packing material shoved up against the lens.  I have not had a chance to look at the night sky with it yet so I'm wondering how much this may affect the view.  The problem is, I cleaned the lens by using one of those alcohol chem-pads and while it removed the scratch, it looks like it removed some of the coating as well.  Here are a couple photos, the first being how it looked before, then after I wiped it down.  It looks like I cleaned it with steel wool.  I blew off the dust first then used the chem-pad and here we are.

 

SlKzcxPl.jpg

 

uqf3omwl.jpg

 

I fogged up the lens on this one to show it better..

 

kXJSi3Ml.jpg

 

And I'm not sure what's going on with this view but it's really spotty around the light.

 

IxodQvTl.jpg



#2 wrnchhead

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Posted 16 September 2020 - 10:59 AM

I’m not a coatings expert but I think that a coating that could be removed with an alcohol wipe would be next to useless. Maybe the entire thing has a layer of schmutz on it and you have just cleaned part of it. (Like wiping a wall in a smokers house) If it were mine I would give the whole thing a good wipe down
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#3 tony_spina

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Posted 16 September 2020 - 11:11 AM

Was this a new scope? What is the make and model? 

 

What cleaning pad did you use?  It's not normal for a glass cleaning pad to remove the coatings 



#4 bicyclemonkey

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Posted 16 September 2020 - 11:22 AM

Here's what I used to wipe the lens.

 

v7CoUIBl.jpg

 

MisoXcMl.jpg



#5 TOMDEY

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Posted 16 September 2020 - 11:23 AM

The good news is that the scope will still work just fine as it ever did. But yeah, it sure looks like you scrubbed off a lot of the coating. If it were me, I'd just use and ennjoy it. I'll guess that you got it used... cheap?    Tom


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#6 bicyclemonkey

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Posted 16 September 2020 - 11:26 AM

I’m not a coatings expert but I think that a coating that could be removed with an alcohol wipe would be next to useless. Maybe the entire thing has a layer of schmutz on it and you have just cleaned part of it. (Like wiping a wall in a smokers house) If it were mine I would give the whole thing a good wipe down

It wasn't too bad but I did wonder if it came from a smokers house.  I was surprised an alcohol pad would have done that but you may be right, it may just be other gunk that needs to be cleaned off.  I don't have any more chem-pads so what would be recommended, alcohol and cotton balls?



#7 bicyclemonkey

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Posted 16 September 2020 - 11:38 AM

The good news is that the scope will still work just fine as it ever did. But yeah, it sure looks like you scrubbed off a lot of the coating. If it were me, I'd just use and ennjoy it. I'll guess that you got it used... cheap?    Tom

I thought it would probably still look ok, the best I've been able to see thru it is trees off in the distance in the daytime and they look fine.  I got it for cheap enough since the seller gave me a partial refund but it wasn't a steal.

 

Was this a new scope? What is the make and model? 

It's a Meade 390



#8 MisterDan

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Posted 16 September 2020 - 11:39 AM

It may not be bad at all.

 

The first thing I would do is simply take the scope for a test drive to check things out.  View a bright target (Jupiter or the Moon's terminator) using a longer-focal-length eyepiece (low power) and see if there is any "come-and-go" flaring or smearing as you move Jupiter (or the edge of the Moon) back and forth across your field of view.  Be sure the eyepiece is clean/clear, of course.  You may see NO effect whatsoever.  Sometimes, even really "ugly" coatings can show absolutely zero effect(s) at the eyepiece.  If you do see any flaring/smearing, then try it  with a couple/few different eyepieces (and at higher magnification, if you can), to see if there's any pattern/consistency in the observed come-and-go smearing (if it's visible at all, of course).  Twist/turn the eyepiece, too.

 

If the objective's coating is indeed "cleaning" away, don't worry.  It happens, sometimes, with older coated optics, and even the safest/most gentle cleaning can (and will) remove degraded coatings.  I have a ~50-year-old Kellner that still works fine despite the fact that the "outer" eyelens coating degraded and completely "cleaned" away, years ago.

 

If, on the other hand, it is indeed "schmutz," and it is negatively impacting your views, then continue with one more gentle cleaning session and see where you are.

 

You will likely get more advice and/or links re: how to gently/safely clean an objective. Do heed that advice.smile.gif

 

Best wishes and luck.

Dan


Edited by MisterDan, 16 September 2020 - 11:58 AM.

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#9 bicyclemonkey

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Posted 16 September 2020 - 12:51 PM

It may not be bad at all.

 

The first thing I would do is simply take the scope for a test drive to check things out.  View a bright target (Jupiter or the Moon's terminator) using a longer-focal-length eyepiece (low power) and see if there is any "come-and-go" flaring or smearing as you move Jupiter (or the edge of the Moon) back and forth across your field of view.  Be sure the eyepiece is clean/clear, of course.  You may see NO effect whatsoever.  Sometimes, even really "ugly" coatings can show absolutely zero effect(s) at the eyepiece.  If you do see any flaring/smearing, then try it  with a couple/few different eyepieces (and at higher magnification, if you can), to see if there's any pattern/consistency in the observed come-and-go smearing (if it's visible at all, of course).  Twist/turn the eyepiece, too.

 

If the objective's coating is indeed "cleaning" away, don't worry.  It happens, sometimes, with older coated optics, and even the safest/most gentle cleaning can (and will) remove degraded coatings.  I have a ~50-year-old Kellner that still works fine despite the fact that the "outer" eyelens coating degraded and completely "cleaned" away, years ago.

 

If, on the other hand, it is indeed "schmutz," and it is negatively impacting your views, then continue with one more gentle cleaning session and see where you are.

 

You will likely get more advice and/or links re: how to gently/safely clean an objective. Do heed that advice.smile.gif

 

Best wishes and luck.

Dan

Hey thanks for all that.  I'm just getting impatient since I haven't had free time to get it outside yet.



#10 JohnBear

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Posted 16 September 2020 - 01:17 PM

I think Wrnchhead's theory of a "layer of schmutz" is probably correct. The chemwipe probably dissolved the schmutz and when the alcohol evaporated the schmutz was redistributed and left behind.

 

Try doing a "proper" optical lens cleaning this time.

 

Use a solution of a drop of soap in a pint of water with about a half cup of isopropyl alcohol. Dab it with on a cotton pad until fairly wet, then wipe of very gently with a clean cotton pad.

Rinse and repeat several times.

When it looks like the schmutz is gone, rinse with pad soaked in distilled water, then dab dry with another clean pad. Repeat several times if necessary until you are amazed at how clean it now looks.

If it is really schmutz-dirty, you may have to repeat this whole process several times.

 

Astronomy is a game that requires patience if you want to get the best results!  

 

A good You Tube video on reflector mirror cleaning demonstrates most of the principles abou being careful while cleaning optical surfaces; except with a refractor you don't want to pour water on the lens and risk getting it inside the tube - hence "dab and dry".


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#11 bicyclemonkey

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Posted 16 September 2020 - 01:30 PM

I think Wrnchhead's theory of a "layer of schmutz" is probably correct. The chemwipe probably dissolved the schmutz and when the alcohol evaporated the schmutz was redistributed and left behind.

 

Try doing a "proper" optical lens cleaning this time.

 

Use a solution of a drop of soap in a pint of water with about a half cup of isopropyl alcohol. Dab it with on a cotton pad until fairly wet, then wipe of very gently with a clean cotton pad.

Rinse and repeat several times.

When it looks like the schmutz is gone, rinse with pad soaked in distilled water, then dab dry with another clean pad. Repeat several times if necessary until you are amazed at how clean it now looks.

If it is really schmutz-dirty, you may have to repeat this whole process several times.

 

Astronomy is a game that requires patience if you want to get the best results!  

 

A good You Tube video on reflector mirror cleaning demonstrates most of the principles abou being careful while cleaning optical surfaces; except with a refractor you don't want to pour water on the lens and risk getting it inside the tube - hence "dab and dry".

Thank you!  I'm going to give this a shot tonight!



#12 Michael Covington

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Posted 16 September 2020 - 02:17 PM

I don't think you took the coating off.   Isopropanol will not do that.   A thin smudge of grease on top of coating looks just like a place where the coating is missing.

Clean it more carefully (I recommend PEC-Pads; definitely use something recommended for fine optics).


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#13 SteveG

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Posted 16 September 2020 - 07:32 PM

I don't think you took the coating off.   Isopropanol will not do that.   A thin smudge of grease on top of coating looks just like a place where the coating is missing.

Clean it more carefully (I recommend PEC-Pads; definitely use something recommended for fine optics).

 

I was thinking the same - looks like grease.

 

You can use lacquer thinner or any other solvent, and a q-tip to clean off the grease, followed by a standard cleaning. Just be sure to keep the solvent away from the cell.



#14 Redbetter

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Posted 18 September 2020 - 04:21 AM

Depending on where the scope was stored:  near a kitchen, in the garage, around heavy smokers, etc. the isopropanol may just have partially removed some grease or other environmental residue.  I would finish cleaning it at this point, I have seen problems associated with broad sections of actual damaged coatings before, and this might behave in a similar way, so just make it uniform by removing the remainder of the gunk.  

 

Beware that liquid can wick or seep down between lenses during cleaning.  This can cause a fog, droplets, or other condensation effects between lenses.  This will probably clear if it happens, but it could take a long time if too much gets in there.  If you aren't prepared to remove the elements for cleaning, pointing the lens face down while cleaning will help.  Take it a section at a time rather than saturating the surface with a bunch of liquid.  




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