Home

Please support mflenses.com if you need any graphic related work order it from us, click on above banner to order!
SearchSearch MemberlistMemberlist RegisterRegister ProfileProfile Log in to check your private messagesLog in to check your private messages Log inLog in

Natural Lens Coating: myth or reality?
Post new topic   Reply to topic
Home   Manual Focus Lenses
View previous topic :: View next topic  


PostPosted: Wed Dec 24, 2014 5:22 am    Post subject: Natural Lens Coating: myth or reality? Reply with quote
A few years ago I bought a 1937 uncoated CZJ 50/1.5 with some issues and had Henry Scherer fix it, which he did very well.

He wrote to me:
"Hello Charlie,
I have an opening while waiting for paint to cure while working on a Contax III and so have moved forward with your lens and it is completely disassembled. It is very dirty but very fine. The lens elements are in perfect condition and so my guess is it's going to be a 10 when its done. It's distinguished by very fine surface oxidation of the front and rear lens elements. This shows it's never been cleaned. Whoever owned it previously cared for it very much. This surface oxidation acts like coating and significantly improves the lens so if I were you I'd invest in a UV filter and would never clean this lens. This surface oxidation is very rare and highly desirable."

Recently a user at RFF found a very interesting converted CZJ 50/1.5 ( http://imgur.com/a/zSQUJ) and I related this information, albeit very briefly, at first, in the following thread:
http://rangefinderforum.com/forums/showthread.php?threadid=146282

another different user who appears to have some knowledge, though not exactly forthcoming with much detail, basically claims this idea is balderdash in the thread above and I defend the proposition with some more detail....that doesn't impress him much LOL

I did some searching for more info, and found some interesting hints, but less detail and examples than I would like. I.e. it's not oxidization exactly, but exposure to halogens? Some glass will do it and other glass will not?

This old lens is seriously sharp, and I have not touched it really since Henry cleaned it. Here are some samples:


L1023014 by unoh7, f/8


L1023017 by unoh7, f/9.5


L1023043 by unoh7, f/5.6


L1023072 by unoh7, f/4

These are not edited.


DSC02414 by unoh7, on Flickr
Not bad for a 75 year old lens which never has seem a drop of lens cleaner Wink
However, for all I know, the guy who claims the natural coating is nonsense may be right...thoughts?


PostPosted: Wed Dec 24, 2014 7:53 am    Post subject: Reply with quote
I recall reading that a buildup of "stuff" lead to the discovery of coatings, I'll try and find that page...
Page 28 of the pdf(2)
http://www.uotechnology.edu.iq/eretc/books/Thin%20Film%20Optical%20Filters.pdf
Quote:
Meanwhile, in 1817, Joseph Fraunhofer had made what were probably the first ever antireflection coatings. It is worth quoting his observations at some length because they show the considerable insight that he had, even at that early date, into the physical causes of the effects that were produced. The following is a translation of part of the paper as it appears in the collected works [9].
Before I quote the experiments which I have made on this I will give the method which I have made use of to tell in a short time whether the glass will withstand the influence of the atmosphere. If one grinds and then polishes, as finely as possible, one surface of glass which has become etched through long exposure to the atmosphere, then wets one part of the surface, for example half, with concentrated sulphuric or nitric acid

and lets it work on the surface for 24 hours, one finds after cleaning away the acid that that part of the surface on which the acid was, reflects much less light than the other half, that is it shines less although it is not in the least etched and still transmits as much light as the other half, so that one can detect no difference on looking through. The difference in the amount of reflected light will be most easily detected if one lets the light strike approximately vertically. It is the greater the more the glass is liable to tarnish and become etched. If the polish on the glass is not very good this difference will be less noticeable. On glass which is not liable to tarnish, the sulphuric and nitric acid does not work. Through this treatment with sulphuric or nitric acid some types of glasses get on their surfaces beautiful vivid colours which alter like soap bubbles if one lets the light strike at different angles


Page 30 of the pdf(4)
Quote:
in 1891, Dennis Taylor published the first edition of his famous book On the Adjustment and Testing of Telescopic Objectives and mentioned [11, 12] that ‘as regards the tarnish which we have above alluded to as being noticeable upon the flint lens of an ordinary objective after a few years of use, we are very glad to be able to reassure the owner of such a flint that this film of tarnish, generally looked upon with suspicion, is really a very good friend to the observer, inasmuch as it increases the transparency of his objective’.
In fact, Taylor went on to develop a method of artificially producing the tarnish by chemical etching [13]. This work was followed up by Kollmorgen, who developed the chemical process still further for different types of glasses


PostPosted: Wed Dec 24, 2014 8:44 am    Post subject: Reply with quote
Nice lens, looks like a keeper, congrats, and, keep it safe.


PostPosted: Wed Dec 24, 2014 10:44 am    Post subject: Reply with quote
Wikipedia -- Glass Disease


PostPosted: Wed Dec 24, 2014 11:39 am    Post subject: Reply with quote
I don't know about the chemistry behind it, but if a lens works so well, who cares? Wink


PostPosted: Wed Dec 24, 2014 3:40 pm    Post subject: Reply with quote
visualopsins wrote:
Wikipedia -- Glass Disease

I don't think this is the same thing we are talking about, this will not help the lens perform better, and i would have to assume it would only effect cheap glass, not optical glass I would think.


PostPosted: Thu Dec 25, 2014 12:02 am    Post subject: Reply with quote
Lightshow wrote:
I recall reading that a buildup of "stuff" lead to the discovery of coatings, I'll try and find that page...
Page 28 of the pdf(2)
http://www.uotechnology.edu.iq/eretc/books/Thin%20Film%20Optical%20Filters.pdf
Quote:
Meanwhile, in 1817, Joseph Fraunhofer had made what were probably the first ever antireflection coatings. It is worth quoting his observations at some length because they show the considerable insight that he had, even at that early date, into the physical causes of the effects that were produced. The following is a translation of part of the paper as it appears in the collected works [9].
Before I quote the experiments which I have made on this I will give the method which I have made use of to tell in a short time whether the glass will withstand the influence of the atmosphere. If one grinds and then polishes, as finely as possible, one surface of glass which has become etched through long exposure to the atmosphere, then wets one part of the surface, for example half, with concentrated sulphuric or nitric acid

and lets it work on the surface for 24 hours, one finds after cleaning away the acid that that part of the surface on which the acid was, reflects much less light than the other half, that is it shines less although it is not in the least etched and still transmits as much light as the other half, so that one can detect no difference on looking through. The difference in the amount of reflected light will be most easily detected if one lets the light strike approximately vertically. It is the greater the more the glass is liable to tarnish and become etched. If the polish on the glass is not very good this difference will be less noticeable. On glass which is not liable to tarnish, the sulphuric and nitric acid does not work. Through this treatment with sulphuric or nitric acid some types of glasses get on their surfaces beautiful vivid colours which alter like soap bubbles if one lets the light strike at different angles


Page 30 of the pdf(4)
Quote:
in 1891, Dennis Taylor published the first edition of his famous book On the Adjustment and Testing of Telescopic Objectives and mentioned [11, 12] that ‘as regards the tarnish which we have above alluded to as being noticeable upon the flint lens of an ordinary objective after a few years of use, we are very glad to be able to reassure the owner of such a flint that this film of tarnish, generally looked upon with suspicion, is really a very good friend to the observer, inasmuch as it increases the transparency of his objective’.
In fact, Taylor went on to develop a method of artificially producing the tarnish by chemical etching [13]. This work was followed up by Kollmorgen, who developed the chemical process still further for different types of glasses


I've been asking about this issue in several forums, and this is the best reply I've seen yet. TY so much for taking the time to post this, LS Smile


PostPosted: Thu Dec 25, 2014 12:22 am    Post subject: Reply with quote
Looks more like urban legend.
Of course it is desirable to have some unique natural coating on some unique lens. It makes it more precious and beautiful.
But the effect to the image quality should be negligible at best (especially if it's claimed to be positive).


PostPosted: Thu Dec 25, 2014 12:49 am    Post subject: Reply with quote
nandakoryaaa wrote:
Looks more like urban legend.
Of course it is desirable to have some unique natural coating on some unique lens. It makes it more precious and beautiful.
But the effect to the image quality should be negligible at best.

Increased contrast was a very desirable quality before coatings became common, that a bit of tarnish increased contrast (by reducing reflections) that it started research into lens coatings, means there must have been something to it.
Belief or non-belief does not constitute proof for or against anything.


PostPosted: Thu Dec 25, 2014 12:51 am    Post subject: Reply with quote
uhoh7 wrote:

I've been asking about this issue in several forums, and this is the best reply I've seen yet. TY so much for taking the time to post this, LS Smile

Glad I could help.
Merry Christmas

James


PostPosted: Thu Dec 25, 2014 4:01 am    Post subject: Reply with quote
Lightshow wrote:
uhoh7 wrote:

I've been asking about this issue in several forums, and this is the best reply I've seen yet. TY so much for taking the time to post this, LS Smile

Glad I could help.
Merry Christmas

James


Best to you also, James Smile

one last from what might or might not be a lens coated by time and the atmosphere Smile

All fall down by unoh7, CZJ 50/1.5 f/9.5ish

It also has the little bubbles deep in the glass Smile


DSC06958 by unoh7, on Flickr


PostPosted: Thu Dec 25, 2014 7:31 am    Post subject: Reply with quote
Your "natural" coating does not make sense imo on the outer surfaces only: 4% reflection in the inner lenses and vagabundig these reflections is the reason for low contrast. So it's more importand the inner air to glass surfaces to be coated.

It's a nice item with good optical results you own, take care of it & use it!

uhoh7 wrote:
... this is the best reply I've seen yet. TY so much for taking the time to post this, LS Smile

+1!
My deep thanks to You Lightshow, for letting us part in the pdf. I'll learn a lot hopefully!

Best x-mas wishes to You all


PostPosted: Thu Dec 25, 2014 11:45 am    Post subject: Reply with quote
Lightshow wrote:

Increased contrast was a very desirable quality before coatings became common, that a bit of tarnish increased contrast (by reducing reflections) that it started research into lens coatings, means there must have been something to it.
Belief or non-belief does not constitute proof for or against anything.


Yes, but concerning the outer surfaces, you can take a coated lens and practically destroy the coating and scratch the glass itself and you will hardly see any impact on the image. That's why I say the effect is negligible.


PostPosted: Thu Dec 25, 2014 2:38 pm    Post subject: Reply with quote
nandakoryaaa wrote:
Lightshow wrote:

Increased contrast was a very desirable quality before coatings became common, that a bit of tarnish increased contrast (by reducing reflections) that it started research into lens coatings, means there must have been something to it.
Belief or non-belief does not constitute proof for or against anything.


Yes, but concerning the outer surfaces, you can take a coated lens and practically destroy the coating and scratch the glass itself and you will hardly see any impact on the image. That's why I say the effect is negligible.


However, you may see loss of contrast, which is the point made -- the effect is, of course, seen more easily, is more prominent, when there is a bright light shining on the lens surface...


PostPosted: Thu Dec 25, 2014 6:48 pm    Post subject: Reply with quote
nandakoryaaa wrote:
Lightshow wrote:

Increased contrast was a very desirable quality before coatings became common, that a bit of tarnish increased contrast (by reducing reflections) that it started research into lens coatings, means there must have been something to it.
Belief or non-belief does not constitute proof for or against anything.


Yes, but concerning the outer surfaces, you can take a coated lens and practically destroy the coating and scratch the glass itself and you will hardly see any impact on the image. That's why I say the effect is negligible.

The coating on the outer surfaces contribute little to contrast(the front in particular, the rear from sensor reflection), the inner surfaces that reflect cause the loss of contrast because that reflected light is scattered and reflected yet again and will eventually reach the sensor/film and will cause that loss of contrast.


PostPosted: Thu Dec 25, 2014 6:57 pm    Post subject: Reply with quote
Lightshow wrote:

The coating on the outer surfaces contribute little to contrast(the front in particular, the rear from sensor reflection), the inner surfaces that reflect cause the loss of contrast because that reflected light is scattered and reflected yet again and will eventually reach the sensor/film and will cause that loss of contrast.


Then there is a question: do inner surfaces also oxidize and acquire that natural coating?


PostPosted: Thu Dec 25, 2014 7:29 pm    Post subject: Reply with quote
nandakoryaaa wrote:
Lightshow wrote:

The coating on the outer surfaces contribute little to contrast(the front in particular, the rear from sensor reflection), the inner surfaces that reflect cause the loss of contrast because that reflected light is scattered and reflected yet again and will eventually reach the sensor/film and will cause that loss of contrast.


Then there is a question: do inner surfaces also oxidize and acquire that natural coating?

There is some air exchanged, so I don't see why not, just takes much longer.


PostPosted: Thu Dec 25, 2014 8:02 pm    Post subject: Reply with quote
So then, any lens that is old enough and wasn't cleaned from inside, should have better contrast.


PostPosted: Fri Dec 26, 2014 12:47 am    Post subject: Reply with quote
nandakoryaaa wrote:
So then, any lens that is old enough and wasn't cleaned from inside, should have better contrast.

It may depend on the glass, coated lenses may not tarnish, it would take lots of careful testing to know for sure what is happening, far more work than I would want to put into it.


PostPosted: Fri Dec 26, 2014 4:03 am    Post subject: Reply with quote
In the early days of photography, exposure to air caused lenses to eventually acquire a sort of natural coating, referred to as "blooming". But rather than it being a detriment, photographers found that lenses afflicted with blooming had increased light transmission and better contrast, because the blooming reduced light scatter. As a result, old camera lenses were highly prized among photographers. Investigation of this phenomenon led to the development of artificial lens coatings, which do for our telescope equipment today what blooming did for old camera lenses, except to a much higher degree.
Source: The Lake County Astronomical Society

The anti-reflective properties of tarnish ("blooming") on optical glass were discovered by Lord Rayleigh in 1886. He observed that old tarnished glass surfaces produced much fewer reflections than freshly polished glass surfaces:


Source: John William Strutt, Baron Rayleigh, Physics, Volume II, 1881-1887, Cambridge University Press, 1900, p.538

Rayleigh tested some old, slightly tarnished pieces of glass, and found to his surprise that they transmitted more light than new, clean pieces. The tarnish replaces the air-glass interface with two interfaces: an air-tarnish interface and a tarnish-glass interface. Because the tarnish has a refractive index between those of glass and air, each of these interfaces exhibits less reflection than the air-glass interface did. In fact, the total of the two reflections is less than that of the "naked" air-glass interface, since for near-normal incidence the reflectivity is proportional to the square of the difference in refractive index.
Source: Wikipedia

Harold Denis Taylor of Thomas Cooke and Sons of York (a telescope manufacturer at the time) in his 1896 book "On the adjustement and testing of telescopic objectives", second edition p.62, noted:

We have seen so many proofs... of the unmistakably increased transparency of tarnish surfaces as compared with freshly polished surfaces.

H. D. Taylor developed a chemical method for producing such coatings in 1904 and patented it. But this process was too difficult to implement due to a lack of repeatability and thus was never used widely. In 1935, Aleksander Smakula, who was working for the Carl Zeiss optics company, patented an industrial method for depositing anti-reflective coating on optical glass to reach 80% transmission. Until 1940, anti-reflective coatings remained a military secret and it's only after WWII that these coatings began to be widely used.

Cheers!

Abbazz


PostPosted: Fri Dec 26, 2014 4:47 am    Post subject: Reply with quote
Wow, Abbazz!

Fantastic post Smile

TY so much for taking the trouble, really interesting stuff to me.

I'm very curious about the chemistry, and would assume there are multiple processes.

We are lucky to live in a time when we can experiment with great old glass on modern digital sensors. I have quite a few pre-1960 lenses but the CZJ 50/1.5 is my only uncoated lens.


PostPosted: Fri Dec 26, 2014 9:19 am    Post subject: Reply with quote
uhoh7 wrote:
Wow, Abbazz!

Fantastic post Smile

TY so much for taking the trouble, really interesting stuff to me.

You're welcome, mate!

Cheers!

Abbazz
Post new topic   Reply to topic
Home   Manual Focus Lenses
Page 1 of 1