Leica Featured: 'Natural coating: myth or reality?' by uhoh7

[uhoh7]

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 (

https://imgur.com/a/zSQUJ

Brian, you will want to check that out) and I related this information, albeit very briefly, at first, in the following thread:
Odd CZJ Sonnar 5cm f/1.5 ! - Rangefinderforum.com

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

Brian, I know you have seen a bunch of these, and other users may have some experience as well. What do you think?

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

However, for all I know, the guy who claims the natural coating is nonsense may be right...thoughts?

 

[Brian]

"Bloom" on the lens is the natural oxidation of glass, acts as a lens coating, and is the phenomenon that led to the application of lens coatings. Look for Neblette, "Photographic Lenses", 1965 edition on Ebay. Great Book.

It is not present on all lenses, some are better than others.

FS: 1936 Carl Zeiss Jena 5cm F1.5 Sonnar custom converted to Leica Thread Mount

So good on this one, I retracted it from sale and kept it. Had offers for full-price after retracting, and made another Sonnar for the person- sold it for $70 less than I priced this on.

This is the picture that made me decide to keep the lens, wide-open on the M9.

https://www.leicaplace.com/album.php?&u=42

Now- I did very carefully- clean my lens, front and rear. I keep a very good multi-coated Schneider UV filter over it. Unless it is on the M-Monochrom. Then I use an Orange filter.

A very special lens in my collection- a 1936 5cm F1.5 Sonnar, factory coated- 190xxxx. I believe that this lens was part of a test run of the vacuum deposition equipment then newly delivered. An RFF member let me know that he had seen another coated lens from this batch, slightly lower SN than mine. This lens had never been worked on when I got it from Ebay. Looked like wax paper when received. My "Naturally Bloomed" lens is from block 198xxxx. I have another uncoated lens from the 190xxxx block within 60 of the one below.

1936 5cm F1.5 Sonnar, coated optics

 

[Brian]

H. Dennis Taylor is credited for recognizing that lenses with a dark tarnish (bloom) transmitted more light than a new lens of the same type. Taylor noted his observations in 1896. Source- "Lenses in Photography", Rudolf Kingslake, 1951.

Neblette also credits H.D. Taylor and writes "The increased light transmission of lenses that had acquired a surface 'bloom' with age was noticed by H.D. Taylor of the firm Taylor, Taylor and Hobson about the end of the 19th century." Source, "Photographic Lenses", Neblette, 1973.

SO- Kingslake and Neblette are on your side of this argument. Those two have "unTarnished" reputations...

Not to mention me, just looking at my own "Blooming" lens and comparing it with a coated lens made the same year as it was.

This is all very transparent to me... I'm on a roll.

So, lets all sit back and REFLECT on this one... it will all be very clear. Surface weatherization of the glass surface changes the index of refraction, increases transmission, and reduces reflections. Once you get a lens with a good bloom, hold onto it- the rare of the rare.

 

[Mijo]

Jeez Brian, you've probably forgotten more about lenses and cameras than I will ever know. The amount of quality information you provide on this forum is both staggering and generous, thank you.

 

[Brian]

Thankyou, it's a hobby. I've been a computer engineer in Optical Sciences for over 35 years. I've had some great optical engineers working for me in the past, learned a lot from them and could ask a lot of questions.

 

[dalethorn]

Amazing stuff!! My reading of Langford's Basic and Advanced Photography in the late 70's didn't mention this at all AFAIK. And any lens that captured that portrait is a star performer.

 

[asiafish]

All I know is that my uncoated 1937 Sonnar with mild bloom and my coated 1963 Jupiter 3 (more bloom) are both outstanding, with the J3 far more flare resistant. Not sure if its the actual coating (well worn) or the bloom that makes my J3 so crisp, but it results in a higher contrast image.

I love them both.

 

[uhoh7]

I'm wondering if a macro shot could capture the oxidation? Is it "oxidization" or another chemical reaction?

Is it quite apparent to you, Brian?

and TY so much for detailed reply.

 

[Brian]

I've read the term "weatherization" used, and recall the term "Oxidation". Looking up the term "tarnish", it is not limited to oxidation and some metals require hydrogen sulfide for tarnish to occur. Both are naturally occurring.

You can see the bloom on the glass when inspecting closely, can see color in the reflection as it is not as even as a traditional lens coating. You can see a difference when looking at multiple samples of the lens set next to each other. I have 3 uncoated 5cm F1.5 Sonnars tight now.

 

[uhoh7]

TY for that, Brian

I have to post this wonderful reply by Lightshow in the MFlenses forum:

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 Film Optical Filters.pdf

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)

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

 

[Brian]

That piece would certainly explain why some lenses show bloom and others do not. I'll try to get a photo of my 1934 lens, it was the easiest to see the color differences across the surface.

According to an article, silver requires the presence of hydrogen sulfide in the air for tarnish to develop. The work of Joseph Fraunhofer also demonstrates that might be a cause for tarnish in glass as well.

 

[Raid]

Now I "must" check my old Sonnar lenses for such a bloom.
I have quite a few old 5cm lenses at home.

 

[uhoh7]

another fantastic post from MF lenses I have to share with you guys:

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

There are a number of other interesting comments in the thread:
Natural Lens Coating: myth or reality?

One user feels the real effect of "tarnish" would be on the inner surfaces, and wonders if this happens.

I'm very curious about the chemistry, and would assume there may be multiple processes involved. I think we are very lucky to have these 75 year old Jenas and the wonderful M9 to experiment with

 

[brusby]

Great articles, thanks!