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Modern Lens Coatings - Refactor Owner Paranoia? Or Reality?

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#1 GregInDE

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Posted 27 February 2020 - 09:20 PM

I come from a heavy photography background -- 30 plus years, with camera gear in tow to all parts of the world, including really harsh environments (African deserts, summits of many mountains, including 24,000+ foot mountains, -40f tundras, etc.).  I've used all sorts of lenses, and one thing about modern high-end lenses is the quality and durability of the optical coatings used in those lenses.  In particular, the external elements of modern photographic lenses are extremely durable due to modern coatings, and flawlessly hold up to multiple and frequent cleanings.

 

In the last year or two, I've rekindled my love for astronomy (largely driven by my young son who has really shown a passion for it).  My first scope when I was 10 was a 4" Meade SCT.  Crappy scope because if I looked at it wrong the collimation would go out.  Always a frustration.  

 

Anyway, we're using a 4.5" APO at the moment, and I'm shopping for a larger APO.  I'm not opposed to buying used, and have had discussions with sellers of 6-7" APOs from fine manufacturers (TEC, TAK, APM, etc.), and many of them are keen to tell me that "I've never cleaned the front element!"  I had one guy send me a pic of the front element of a TOA 130 and it looked like someone ate mac-n-cheese  off of it because it was so filthy.

 

But why?  Are the coatings on good, modern refractors so soft and delicate that a gentle cleaning will wound the scope forever?  Are the front element coatings that much less durable than the front elements on the good, modern photograhpic lenses from Canon, Nikon or Sony?

 

Or are astro refractor people just paranoid?

 

Asking honestly, because I just don't know if the coatings on front elements of high-end refractors are completely different from photographic lenses.  And, to be clear, I'm mostly interested in the offerings from the better refractor builders -- as I said above, TEC, Tak, APM, CFF, SV, etc.

 

Coatings.  Hummm.   Thoughts?


Edited by GregInDE, 27 February 2020 - 09:21 PM.

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#2 Jeff B

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Posted 27 February 2020 - 09:41 PM

"Or are astro refractor people just paranoid?"

 

Bingo.  And let's not forget eyepiece coating nervosa either.

 

Actually good old single layer MgFl coatings are very durable and just fine for the front elements, but like all coatings, they need to be applied properly.

 

Jeff


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#3 Alan French

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Posted 27 February 2020 - 09:59 PM

I think people worry far too much about cleaning modern lenses. When I see someone selling a scope and claiming "The lens has never been touched" I cringe, thinking the telescope was not properly cared for. You don't want to overdo it, but some of the gunk that accumulates is not good for coatings and only gets more difficult to remove over time. 

 

Clear skies, Alan


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#4 TOMDEY

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Posted 27 February 2020 - 10:30 PM

"Hard" dielectric external-surface antireflection coatings should, in theory and practice, be just about as cleanable as bare glass. They almost always comprise multiple alternating quarter-wave layers of TiO2/SiO2 with some trademark/tradename proprietary nuances that generally are more marketing mumbo-jumbo than truly innovative. They should withstand periodic, sensible cleanings, without damage. I agree with Jeff and Alan that many astro fans are paranoid to the point of paralysis. Most damage that we witness came from either faulty application at the factory or stupidly-abusive field use and then ham-handed scrubbing with the closest rag. I have lenses decades old that are still functionally perfectish.

 

Please note that MgF2 and ZnS are also  decent coating materials, but are considered "Soft". they are cleanable, but not nearly so durable as those other dielectrics mentioned above. And Cryolite Na3AlF6 has fantastic optical properties, but is soft as butter. Long list of other candidate dielectrics, Al2O3 etc. etc.

 

All that said, coatings will eventually wear from abuse and/or cleanings. Nothing is ~forever~

 

[I was a coating engineer/scientist at B&L for twelve years, with quite a few coating patents. Most of our coatings were for the big lighting companies, military and commercial optics. Proper application is the key.]    Tom


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#5 AposkiiLola

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Posted 27 February 2020 - 10:32 PM

Quite honestly, Zeiss himself is confident enough to publish that we should "dig in there with your finger nail a bit." 

 

So yea it is typical of a human being a fradie cat on that $5000 investment. As stated above,  Refactor optics are not so sensitive anymore when compared to ; lets say a raw silver coated mirror, or a pure fluorite crystal.    Now a days mirrors have a "silicon dioxide" protective over coat layered on the metal surface of a mirror, or some other dielectric coating that is forcefully embedded via ion bombardment directly into the glass pores.

 

There is a right and wrong way for everything, and with optics you typically should focus on the cleaning solution itself and also the type of cloth used.  Lint-free kimwipes for example are specifically made for cleaning all sort of optics.

 

But again, it does depend on the coating a little bit for exotic optics; a Zinc selenide optic can be destroyed just by touching it with a bare finger.

 

Just out of habit you should almost always wear the "white gloves" because your finger print oils and acid's will no doubtfully end up on whatever you are handling just due to nervousness.

 

Another issue is the type of water you are using, as most sink's have lots of minerals and chemicals like chlorine which can end up leaving a white residue.

 

So while there are a bit of annoyances, it certainly is nothing to be scared of.    


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#6 RichA

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Posted 28 February 2020 - 12:09 AM

There are machines made that test coating durability.  Scratch tests that kind of thing.  Problem is, they cost a lot

of money.


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#7 Kunama

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Posted 28 February 2020 - 02:48 AM

The very first thing I did when I got my 'New to me'  TMB-LZOS home was to take the scope apart and clean it, though it wasn't bad I decided that the fine dew, salty air and other deposits had to go:

 

I also cleaned my TOA and FSQ, a bit of research on the methods and testing on cheaper optics, then finally saliva for those stubborn marks ........ I use the Roland C method for my cleaning chores...

Attached Thumbnails

  • MIS_7652.jpg

Edited by Kunama, 28 February 2020 - 03:43 AM.

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#8 ManuelJ

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Posted 28 February 2020 - 03:02 AM

Brought a second hand eyepiece to one of those "I never clean my eyepieces because I read it in a forum". After cleaning the lens, the coatings were damaged by the dust itself.

 

Please just clean with care when needed.


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#9 Thomas Marshall

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Posted 28 February 2020 - 03:50 AM

I'll ask the dumb question, - since they have the techskill now, why don't they layer these expensive lenses with Diamond, and make them virtually unscratchable? 



#10 25585

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Posted 28 February 2020 - 06:43 AM

For photography I use Zeiss UV T* filters screwed over the lens to protect them. But that is not possible for telescopes most often, apart from small aperture models.

 

If there is likely too much muck in the air, I choose a less expensive scope to view with.    

 

So many things to worry about, sometimes it's better to switch off & just look at the sky! 



#11 Jon Isaacs

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Posted 28 February 2020 - 07:21 AM

Lint-free kimwipes for example are specifically made for cleaning all sort of optics.

 

I would not use a Kimwipe on a mirror.  Overcoated or not, mirrors are soft and can retain grit, any sort of cloth or fabric can scratch them. 

 

Actually Kimwipes are designed for general laboratory use.  In the laboratory I ran, we bought both sizes several cases at a time.  They happen to be lint free which gives them an advantage over unscented Kleenex but Roland Christen of Astro-Physics has recommended using Kleenex for all but the final stage of cleaning.  

 

Telescopes are used at night so lens see a lot of dew.  When it dries, it can adhere dust to the lens so some care is needed.. 

 

Jon


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#12 Hermie

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Posted 28 February 2020 - 07:26 AM

I suspect that at least a little of the astronomical cleaning aversion has something to do with those who start on the reflector side of the road. Newt mirrors are very easily damaged, and if you start that way you tend to always treat all your optics very gingerly.


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#13 Mr. Mike

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Posted 28 February 2020 - 08:10 AM

Brought a second hand eyepiece to one of those "I never clean my eyepieces because I read it in a forum". After cleaning the lens, the coatings were damaged by the dust itself.

 

Please just clean with care when needed.

Thats the key.  I clean my eyepieces from time to time and simply use a bulb blower, Kimwipes, an alcohol/solvent free liquid and gentle pressure.  Never had a scartch or an issue. Ever.


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#14 TOMDEY

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Posted 28 February 2020 - 09:25 AM

I'll ask the dumb question, - since they have the techskill now, why don't they layer these expensive lenses with Diamond, and make them virtually unscratchable? 

Cool! But, alas... Diamond is a crystalline state of carbon, pure carbon. The mechanism of thermal vacuum evaporation deposition is that you heat the source material with an electron beam and it entirely ionizes into its components and redeposits onto the substrate, where it reactively recombines, oxidized to the desired state. There is a lot of electric and magnetic stuff going on in there and added blush of gases ~just so~ to get the species to deposit as desired, without raising the absorption coefficient k. Diamond is formed under extremely high pressure aka the exact opposite of the vacuum environment. Short answer --- the physical chemistry / physics of the process environment doesn't support true diamond coating. What you see described as "Diamond Coating" in e.g. TV Infomercials --- that's only Marketing Tradename mumbo-jumbo. Actually has nothing to do with the chemistry of the true diamond state of carbon... nor is it even truly hard.    Tom


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#15 Ihtegla Sar

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Posted 28 February 2020 - 09:55 AM

I suspect that at least a little of the astronomical cleaning aversion has something to do with those who start on the reflector side of the road. Newt mirrors are very easily damaged, and if you start that way you tend to always treat all your optics very gingerly.


Some of it is from manufacturers warnings. The Tak I bought last year warned against over cleaning and recommended cleaning not more often than once every three years.

Personally I would be a lot less worried about cleaning a mirror since the process for cleaning them is so much easier and you can always recoat a mirror if needed.
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#16 Jon_Doh

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Posted 28 February 2020 - 09:57 AM

I have a lot of expensive camera equipment -Leica and Canon L lenses and and I clean my refractors and eyepieces the same as I do my photography stuff.  First, I blow off dust and debris with a Rocket blower and if that doesn't work I use a photo micro fiber cloth.  Been doing it this way for years without any problems.


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#17 Mr. Mike

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Posted 28 February 2020 - 11:11 AM

I have a lot of expensive camera equipment -Leica and Canon L lenses and and I clean my refractors and eyepieces the same as I do my photography stuff.  First, I blow off dust and debris with a Rocket blower and if that doesn't work I use a photo micro fiber cloth.  Been doing it this way for years without any problems.

Yep - Im continually amazed at the panic & outright bad advice thrown around regarding cleaning fine optics.  Its NOT that hard and no one has ever died doing it.  smile.gif

 

A Bulb type blower, a quality wiping mechanism, quality fluid and a gentle demeanor is all you need.  Ive done objective lenses on refractors for years and they look good as new when Im done. Same for my eyepieces which include the "good stuff" like TV, pentax, etc.  Zero problems. Just dont clean too often.  Only as needed.  I find that my eyepieces need a little more frequent de-gunking/cleaning than my objective lenses do.


Edited by Mr. Mike, 28 February 2020 - 11:12 AM.

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#18 m9x18

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Posted 28 February 2020 - 11:33 AM

Here is a short but fun to read December 2006 CN article on lens cleaning written by Ron B[ee]. It describes his first experience cleaning his TV-102.

 

https://www.cloudyni...for-santa-r1544

 

Run your curser over the lens photo to see the before and after pictures.



#19 Ihtegla Sar

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Posted 28 February 2020 - 11:56 AM

Yep - Im continually amazed at the panic & outright bad advice thrown around regarding cleaning fine optics.  Its NOT that hard and no one has ever died doing it.  smile.gif

 

A Bulb type blower, a quality wiping mechanism, quality fluid and a gentle demeanor is all you need.  Ive done objective lenses on refractors for years and they look good as new when Im done. Same for my eyepieces which include the "good stuff" like TV, pentax, etc.  Zero problems. Just dont clean too often.  Only as needed.  I find that my eyepieces need a little more frequent de-gunking/cleaning than my objective lenses do.

Well, there is a difference between using a bulb blower and wiping.  Takahashi recommends using a bulb blower frequently but only wiping once every three years for their new FC line of refractors, provided you have used some care in storing and using your telescope.  They are also very specific about what types of fluids not to use. After about a year of use there is some dust but very little and its only really visible under a flashlight.

 

I have yet to wipe either of my FC Taks, but I use a bulb blower on them after each use before putting the end cap on.  It's pretty hard to damage anything using a bulb blower and they are very effective at blowing off loose dust.


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#20 Spikey131

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Posted 28 February 2020 - 01:08 PM

My scopes don’t get dirty from storage.  They are in their cases indoors whenever they are not pointed at the sky.  They get dirty from use.

 

The problem with my scopes is that they are pointed at the sky for several hours every chance I get, often several times per week.  The wind blows, there is pollen, dew falls.  I take my scopes with me to places near the ocean.

 

If I waited 3 years to clean my objectives, I might as well be looking through newspaper.

 

So I use my gear, store it properly and clean it properly whenever it is needed.  Dust does not bother me.  But if you leave a piece of glass pointed at the sky, it will accumulate soiling that needs to be cleaned.


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#21 Mr. Mike

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Posted 28 February 2020 - 01:30 PM

Well, there is a difference between using a bulb blower and wiping.  Takahashi recommends using a bulb blower frequently but only wiping once every three years for their new FC line of refractors, provided you have used some care in storing and using your telescope.  They are also very specific about what types of fluids not to use. After about a year of use there is some dust but very little and its only really visible under a flashlight.

 

I have yet to wipe either of my FC Taks, but I use a bulb blower on them after each use before putting the end cap on.  It's pretty hard to damage anything using a bulb blower and they are very effective at blowing off loose dust.

TAK is correct - cleaning if it all should be very infrequent.  A bulb blower each use is the right call.  Every here and there you might get something on your objective though that does need to come off.  This is the only time Id ever actually clean the scope lens.  They know their coatings best, right? ;)

 

Its the Eps that get more mucked up.  Even then, I dont go crazy with cleaning, only whan clearly neccessary.


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#22 Sketcher

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Posted 28 February 2020 - 02:35 PM

Refractor owners come in any and all flavors imaginable -- and then some!bounce.gif bugeyes.gif FarmerRon.gifTelescope.gif  gramps.gif Ihavenojoints.gif sumo.gif

 

I think it comes down to a bit of anything and everything.  Some people fear inflicting more damage than that caused by the filth on their optics.  This. probably mostly by people who have never learned how to properly clean their optical surfaces.  Surfaces ought to be cleaned as soon as is reasonably possible -- when they need cleaned.

 

I'm one of those strange people who cause Alan to "cringe".  I have optics that have very rarely been cleaned.  It's a bit like shoes.  Some people walk through mud puddles.  Others only wear that pair of shoes on the operating room floor.  If you can avoid getting them dirty, you can avoid unnecessary cleanings.  The elimination (avoidance) of moisture condensing on optical surfaces, and the use of a bulb-blower to blow off particulates that have landed on a surface by the end of one's observing session go a long way in minimizing the need for cleanings.  Then there's keeping the (dry) optics and telescope capped and cased when not in use.

 

Since I observe alone, I don't encounter all the nastiness that can come from others (smoking, filthy-grimy-inquisitive fingers, etc.) in my immediate area.  And pollen?  Air pollution?  What are those things?lol.gif

 

So, while I rarely clean my optics, I'm a big believer in only using my telescopes when their optics are as clean as they can possibly be.  I often push my telescopes to extremes when it comes to ferreting out subtle and/or faint details.  I'm not going to handicap my efforts by using dirty optics.

 

As for that dirty telescope someone's trying to sell . . .  I don't know, it's anyone's guess as to what lies beneath all that mac-n-cheese.  But I would be more comfortable in cleaning that lens myself rather than "trusting" it to the current owner who has allowed it to arrive in its current condition.


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#23 mikeDnight

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Posted 28 February 2020 - 04:17 PM

I come from a heavy photography background -- 30 plus years, with camera gear in tow to all parts of the world, including really harsh environments (African deserts, summits of many mountains, including 24,000+ foot mountains, -40f tundras, etc.).  I've used all sorts of lenses, and one thing about modern high-end lenses is the quality and durability of the optical coatings used in those lenses.  In particular, the external elements of modern photographic lenses are extremely durable due to modern coatings, and flawlessly hold up to multiple and frequent cleanings.

 

In the last year or two, I've rekindled my love for astronomy (largely driven by my young son who has really shown a passion for it).  My first scope when I was 10 was a 4" Meade SCT.  Crappy scope because if I looked at it wrong the collimation would go out.  Always a frustration.  

 

Anyway, we're using a 4.5" APO at the moment, and I'm shopping for a larger APO.  I'm not opposed to buying used, and have had discussions with sellers of 6-7" APOs from fine manufacturers (TEC, TAK, APM, etc.), and many of them are keen to tell me that "I've never cleaned the front element!"  I had one guy send me a pic of the front element of a TOA 130 and it looked like someone ate mac-n-cheese  off of it because it was so filthy.

 

But why?  Are the coatings on good, modern refractors so soft and delicate that a gentle cleaning will wound the scope forever?  Are the front element coatings that much less durable than the front elements on the good, modern photograhpic lenses from Canon, Nikon or Sony?

 

Or are astro refractor people just paranoid?

 

Asking honestly, because I just don't know if the coatings on front elements of high-end refractors are completely different from photographic lenses.  And, to be clear, I'm mostly interested in the offerings from the better refractor builders -- as I said above, TEC, Tak, APM, CFF, SV, etc.

 

Coatings.  Hummm.   Thoughts?

I think in part that people who pay an awful lot of money for a top class refractor, are just being very careful not to scratch or sleek the coatings. And the more they are cleaned, the greater the chance of injury. Once scratched, the value of the telescope plummets into the abyss.  

Coatings are as tough as old boot, but if a sharp particulate isn't removed before wiping, it can still cut through the coating, ruining the resale value.


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#24 peleuba

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Posted 28 February 2020 - 05:11 PM

Even then, I dont go crazy with cleaning, only whan clearly neccessary.

 

Yes - ONLY when necessary, but ALWAYS when necessary.

 

Grit and grime on a lens needs to be cleaned.  In my neck of the woods it can consist of tree sap, fire place smoke and pollen. 


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#25 barbie

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Posted 28 February 2020 - 05:39 PM

I have a blower bulb and a Tak lens cleaning kit but don't forsee much of a problem or need to clean my objective lenses anytime soon because I am seldomly out long enough for dew and other airborne stuff to excessively collect on their surfaces enough to even justify a yearly cleaning. My classic Tak FC76 has very little dust on the outside of the lens and my Tak FC76 DCUQ I just obtained so no cleaning necessary there either, for now. Both are stored in their cases with dust caps on when not in use.


Edited by barbie, 28 February 2020 - 05:42 PM.



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