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Heavy Duty Objective Cleaning

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#1 NearVision

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Posted 31 October 2024 - 12:30 PM

As background:

I was given a Meade 390 that was in pretty sad shape. The owner found it in a basement cleanout and they knew that it had sat through a few basement floods.

 

Mechanically it's in surprisingly good shape. The OTA had a lot of dirt that cleaned off fairly easily. Cosmetically the hardware is showing rust and corrosion, but not horrible. The tube has numerous scuffs to the paint so even without the flooding it had a rough life. I've gotten it cleaned up enough to use and it gives some nice views.

 

The only thing I'd like to work on some more is the front objectives still have what looks like mineral deposits or fogging on all surfaces after cleaning a few times. I've done some research and found this topic https://www.cloudyni...e-of-meade-390/ that got it looking a lot better. I also tried leaving the glass to soak in the Sun in a tray of vinegar for a few days thinking that might help dissolve the deposits still there. It helped a little but not totally clean.

 

At this point I'm wondering if there is anything else I can do at home to clean them better. I don't really need the scope, I've got a similar size already, but this feels like one of those projects to restore it back to as close to original condition as possible on my own. I know I could probably send them out somewhere to get stripped and recoated but I don't think I want to spend that much.

 

I can use it as is. The views aren't visually hampered by the slight fogging/deposits on the lens. I'm just being curious on how far I can push the cleaning envelope.

 

Any suggestions? smile.gif

Tom



#2 SoCalPaul

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Posted 31 October 2024 - 12:45 PM

I did not fully read that previous thread, so maybe this was already covered. Year ago, I acquired an older, 6" AP refractor. They suggested acetone for cleaning.

 

Clear skies,

Paul



#3 NearVision

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Posted 31 October 2024 - 01:03 PM

The TeleVue article referenced mentions acetone and alcohol. I've tried both with little affect. At this point I think it's either mineral deposits or a chemical reaction in the lens coatings. If it is minerals I'm hoping someone has a good suggestion to dissolve them with damaging the glass and any coatings on it. If it turns out to be  a reaction in the original coating material then I'll probably live with it and not get them recoated.

 

I know I could clean the minerals with a strong cleaner (Rust-Off or something similar) or acid but I don't want to start that and cause more damage to the coatings or etch the glass!



#4 photoracer18

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Posted 31 October 2024 - 01:37 PM

If it got damp its likely fungus. Only thing that works is UV light. Sometimes direct sunlight can work and at other times you need an intense UV light. I used to have a UV programmable IC chip eraser I used in the 1980's, mainly for classic lenses I used to buy at camera swap meets. No idea where it is now and don't know if someplace like Newark or Grainger would still have those things since the use of that technology is pretty much gone.

As a further note the fungus is generally from impurities in the Canadian balsam that was commonly used as lens cement in the old days. Also the fungus can attack the lens coatings from underneath and etch the glass itself. If that is the issue it may not be work repairing


Edited by photoracer18, 31 October 2024 - 01:43 PM.


#5 MisterDan

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Posted 31 October 2024 - 02:00 PM

A photo or two might provide some good perspective.  Some folks may recognize the blemishes/anomalies, and they may have some insight and advice.

 

Best wishes.

Dan


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#6 Oregon-raybender

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Posted 31 October 2024 - 02:43 PM

I would suggest just distilled water (warm) and Dawn soap to start.

90% alcohol to remove any oils. Acetone is last material to use.

You have to be careful is any plastic will melt with Acetone, that

is why I don't use (It's use in production of optics, to remove pitch and

such)

 

But it would be helpful to take an image of the issues.

 

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#7 Bob4BVM

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Posted 31 October 2024 - 03:28 PM

Sounds like an old lens I have. part of it has what appears to be a faint water-staining.

I have seen the same-looking stain on old window glass that was stored stacked together and had been wet for a long time.   It is not fungus or any similar soiling, just a faint but visible greyish stain. Cannot be felt when touching the glass surface

 

Have tried all the usual cleaners with zero results. Maybe it is a faint mineral deposit from water/dew which remained on glass over a long duration. 

Have considered light polishing with finest rouge, or doing a small spot with muriatic acid which would remove any mineral deposit if thats what it is, but do not want to mess up the surface or figure of the lens.

 

BTW the lens is bare glass, uncoated.

Would be curious of what you find to fix yours as it sounds similar to what i have.


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#8 NearVision

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Posted 31 October 2024 - 05:21 PM

I'll try again to get some photos. Catching the right angle is tricky.

 

Bob, what you describe sounds like what it is. I've seen similar staining on old glass. My house has some windows with 100+ year old glass in them that look similar. You're right. It can't be felt. Good to know that they are not coated.

 

Seeing as it is uncoated glass I may try some CLR or something like it that's supposed to remove hard water stains from bath fixtures.



#9 Oregon-raybender

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Posted 31 October 2024 - 05:45 PM

If the lenses are uncoated, I would try white tooth paste, with chalk.

I have removed many stains like this. I surprised many optical engineers

when I use chalk powder (but tooth paste is easier to find). I would

place some on the cotton swab and lightly rob in a circle pattern.

Try for 10-15 seconds, check the surface, repeat if needed.

 

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#10 Bob4BVM

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Posted 31 October 2024 - 05:57 PM

If the lenses are uncoated, I would try white tooth paste, with chalk.

I have removed many stains like this. I surprised many optical engineers

when I use chalk powder (but tooth paste is easier to find). I would

place some on the cotton swab and lightly rob in a circle pattern.

Try for 10-15 seconds, check the surface, repeat if needed.

 

Starry Nightswaytogo.gif

Bob,

I have plenty of chalk (precip, for silvering process), I will try that.

But toothpaste is a mild abrasive, you think it might leave a dulled surface on the glass ?

Thx,

Bob



#11 Oregon-raybender

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Posted 01 November 2024 - 02:38 PM

Hi Bob

 

The chalk grit size in "white" toothpaste is about the same as the powder.

Just make sure that label and product states that chalk is used.

 

You should try it on window or other type of glass first, and see what you think

I use it on car windshields and (yes Windex or RainX), but Dawn

mostly. It works really great. The manufacturers of tooth paste

don't want folks having a gritted feeling while brushing, not like

baking soda. 

 

It's important to rub softly, slight pressure on optical glass.

I mix it with DS water and Dawn. then use small circle patterns.

I had not issues.

 

Starry Nightswaytogo.gif



#12 Bob4BVM

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Posted 01 November 2024 - 03:25 PM

Hi Bob

 

The chalk grit size in "white" toothpaste is about the same as the powder.

Just make sure that label and product states that chalk is used.

 

You should try it on window or other type of glass first, and see what you think

I use it on car windshields and (yes Windex or RainX), but Dawn

mostly. It works really great. The manufacturers of tooth paste

don't want folks having a gritted feeling while brushing, not like

baking soda. 

 

It's important to rub softly, slight pressure on optical glass.

I mix it with DS water and Dawn. then use small circle patterns.

I had not issues.

 

Starry Nightswaytogo.gif

OK i will give it a shot when i get time

Thanks for the tips

Bob



#13 Starman1

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Posted 01 November 2024 - 03:55 PM

Sounds like an old lens I have. part of it has what appears to be a faint water-staining.

I have seen the same-looking stain on old window glass that was stored stacked together and had been wet for a long time.   It is not fungus or any similar soiling, just a faint but visible greyish stain. Cannot be felt when touching the glass surface

 

Have tried all the usual cleaners with zero results. Maybe it is a faint mineral deposit from water/dew which remained on glass over a long duration. 

Have considered light polishing with finest rouge, or doing a small spot with muriatic acid which would remove any mineral deposit if that's what it is, but do not want to mess up the surface or figure of the lens.

 

BTW the lens is bare glass, uncoated.

Would be curious of what you find to fix yours as it sounds similar to what i have.

Ah.  Had the same thing in an Alvan Clark refractor that had sat in a basement for decades.

It took sulfuric acid and a 3 day soak, but the glass came out clean.

If the lens had been coated (it wasn't of course), the acid might have removed the coatings.

But if you have an uncoated lens, gradually stronger and stronger acids, starting with acetic, then nitric, then hydrochloric, then sulfuric, might be required.

None of those acids will harm the glass.  They will dissolve balsam cement, however.

It was with that old Clark lens.  We respaced it with aluminum foil shims, as Clark used postage stamps (!).


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#14 AndresEsteban

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Posted 03 November 2024 - 04:24 PM

As background:

I was given a Meade 390 that was in pretty sad shape. The owner found it in a basement cleanout and they knew that it had sat through a few basement floods.

 

Mechanically it's in surprisingly good shape. The OTA had a lot of dirt that cleaned off fairly easily. Cosmetically the hardware is showing rust and corrosion, but not horrible. The tube has numerous scuffs to the paint so even without the flooding it had a rough life. I've gotten it cleaned up enough to use and it gives some nice views.

 

The only thing I'd like to work on some more is the front objectives still have what looks like mineral deposits or fogging on all surfaces after cleaning a few times. I've done some research and found this topic https://www.cloudyni...e-of-meade-390/ that got it looking a lot better. I also tried leaving the glass to soak in the Sun in a tray of vinegar for a few days thinking that might help dissolve the deposits still there. It helped a little but not totally clean.

 

At this point I'm wondering if there is anything else I can do at home to clean them better. I don't really need the scope, I've got a similar size already, but this feels like one of those projects to restore it back to as close to original condition as possible on my own. I know I could probably send them out somewhere to get stripped and recoated but I don't think I want to spend that much.

 

I can use it as is. The views aren't visually hampered by the slight fogging/deposits on the lens. I'm just being curious on how far I can push the cleaning envelope.

 

Any suggestions? smile.gif

Tom

An excellent approach suggested by a friend of mine who used to work cleaning microscope optics is to use a soft polish wax for car paint. The carnauba wax with some mild abrasive incorporated to the product will do the trick. Usually they come as a semi liquid solution you can apply with a microfiber cloth. This implies you'll do some polish after applying the product over the objective surface, but it will be minimal and remove the whitish layer on the lens without damaging the original coating layer. This is should be a meticulous work but usually it does the trick!

Clear skies for as all!
Andy



#15 luxo II

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Posted 03 November 2024 - 05:20 PM

The chalk grit size in "white" toothpaste is about the same as the powder.

Careful - the grit in toothpaste is aluminium oxide - not chalk - and will eventually turn a highly polished surface cloudy.

Likewise I definitely would NOT use the stuff intended for car paints - that contains alumina, ie aluminium oxide.


Edited by luxo II, 03 November 2024 - 07:43 PM.


#16 photomagica

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Posted 04 November 2024 - 12:32 AM

OMG! Be very careful with abrasives and polishes. It is quite possible to change the figure of the lens in addition to doing damage to the surface.  In the one instance where I had to service a lens with a badly damaged coating and surface due to corrosive vapor exposure I removed the badly deteriorated coating and polished out the surface damage with a pitch lap and cerium oxide in order to maintain the figure.

 

I'd definitely exhaust the possibilities of solvents and acids before turning to abrasive or polishing methods. If I had to polish out a problem I'd definitely use a pitch lap, optical polishing compounds and take care to measure and control the overall lens correction. Test solvents and acids along an edge, the part covered by the lens flange first, to evaluate risk.

Bill


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#17 Oregon-raybender

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Posted 04 November 2024 - 03:17 AM

I would not use car polish, it also has chemicals that are not

good for optics.

 

A far as toothpaste, yes there is in some

that have Hydrated Silica which is milled to small size. Look 

for Chalk (Calcium carbonate) as the first ingredient.

Also some have dicalcium phosphate another polishing

agent. The size is milled enough to not cause sub-surface

sleeking. I had not any issues with them both. If there is

concern, I suggest getting the chalk powder.

 

Starry Nightswaytogo.gif

 

 

https://en.wikipedia...Hydrated_silica

 

https://en.wikipedia...lcium_phosphate


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#18 Bob4BVM

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Posted 04 November 2024 - 01:18 PM

I would not use car polish, it also has chemicals that are not

good for optics.

 

A far as toothpaste, yes there is in some

that have Hydrated Silica which is milled to small size. Look 

for Chalk (Calcium carbonate) as the first ingredient.

Also some have dicalcium phosphate another polishing

agent. The size is milled enough to not cause sub-surface

sleeking. I had not any issues with them both. If there is

concern, I suggest getting the chalk powder.

 

Starry Nightswaytogo.gif

 

 

https://en.wikipedia...Hydrated_silica

 

https://en.wikipedia...lcium_phosphate

OK, i have a 5# bag of the chalk (precip. CaCO3) so i will try that first when i have the lens apart, then on to the acids if that does not work.

My guess is the Muriatic (dilute HCl ) is going to just wipe it off as it does with water stains on the shower door.

-B


Edited by Bob4BVM, 04 November 2024 - 01:21 PM.



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