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Early coating of Leitz lenses


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I've seen references to the earliest coating of Leitz lenses being done by a 'drip coating method' as opposed to the vacuum coating done by Zeiss. I wonder if anyone can educate me (in simple terms!) as to how that was done, and when did Leitz switch over to the other method.

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The benefits of lens coating were known by 1900, but by accident. You might have seen how some old glass bottles turn purple. That is caused by a chemical oxidizing, sometimes by constant exposure to sunlight. Manufacturing coatings was not in the science at the time.

 

Some early attempts at coating used mild acid treatment, sometimes with a gelatin included. That might be called a dip process. I have some early German lenses of that type on Ikontas. The coating is so soft that it is almost always gone due to lens cleaning.

 

As you noted, Zeiss invented the vacuum evaporation method in 1934 or so. The advancement of lens coating was stifled during WWII because Germany made it a military secret.  Leitz's first coated lens was the Summitar 50mm F/2 after the end of WWII. Earlier Summitars were not coated.

 

A curious aside - Old large format lenses were not coated, but over the years some had glass surfaces that oxidized which increased light transmission by acting much like a coating. Funny, but a well cared for (or not used) very old lens is likely better than the day it was manufactured.

Edited by pico
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An interesting snippet of history is the existence of NV Van Leer's Optische Industrie in Delft, also know as  Oude Delft Optische Industrie, later Oldelft, now a part of the  Enraf-Nonius Group.

The founder, Oscar van Leer, and his partner Prof. Brouwer perfected a coating process called "Delfineren". As van Leer was Jewish the German occupation saw his factory confiscated, but Frits Philips managed to keep it going. The patents, however were transferred to Germany (presumably Leitz ), who were able to integrate the process and perfect the rather primitive coating system they were using.

After the war the factory got their process returned and went on as they started before the war, and until the mid 1950-ies they would coat old and new uncoated lenses, which can be confusing if one finds a coated example of for instance a pre-war Leica lens.

As a sidenote, Oude Delft made a number of interesting LTM lenses after the war, the most spectacular of which was the Rayxar 50 mm 0.75 (!)

The most commonly found one is the Minor 35mm  4.6.

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Old Delft made three mirror lenses for Leica, Contax and others - 40cm/f5.0 Fototel, 45cm/f5.6 Fototel and 50cm/f6.3 TD50 (and Fototel?).  The lenses were also sold by Wollensak with their name in the US.  The mirror is built into the lens, so a reflex housing is not used.  The lens mounts directly to the camera.

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As a sidenote, Oude Delft made a number of interesting LTM lenses after the war, the most spectacular of which was the Rayxar 50 mm 0.75 (!)

This was not an LTM lens. The lens was optimized for their x-ray products. 

I worked for them in 1961 in the laboratory. But for only 2 months, I decided to start a study in Delft. 

It was an industrial lens perhaps 5 times heavier as my IIIf. No rangefinder coupling and I remember, that the LTM throat would be too small.

They produced a 35mm LTM lens, I almost bought. 

"Delfineren" was a common term there.

Jan

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An interesting snippet of history is the existence of NV Van Leer's Optische Industrie in Delft, also know as  Oude Delft Optische Industrie, later Oldelft, now a part of the  Enraf-Nonius Group.

The founder, Oscar van Leer, and his partner Prof. Brouwer perfected a coating process called "Delfineren". As van Leer was Jewish the German occupation saw his factory confiscated, but Frits Philips managed to keep it going. The patents, however were transferred to Germany (presumably Leitz ), who were able to integrate the process and perfect the rather primitive coating system they were using.

After the war the factory got their process returned and went on as they started before the war, and until the mid 1950-ies they would coat old and new uncoated lenses, which can be confusing if  ever one finds a coated example of for instance a pre-war Leica lens.

Thank you for this very interesting piece of information - I wonder if you can say anything further about the van Leer/Brouwer process, or the 'rather primitive coating' process and the integration of the Dutch system with contemporary German practice.

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I am too superficial an "expert" for a detailed answer, and a lot has been lost in the convoluted company history.

As far as I am aware it was a chemical process which was said at the time to "increase iridescence"  on the glass surface.

Maybe Jan can tell us more.

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...As van Leer was Jewish the German occupation saw his factory confiscated, but Frits Philips managed to keep it going. The patents, however were transferred to Germany (presumably Leitz ), who were able to integrate the process....

 

That's a little and intriguing piece of history.... when considered it in the context of the  honest and proactive attitude towards Jewish people that Leitz demonstarted in those years (the famous "freedom train")...

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The movement of patents in war time is in itself a fascinating, though frequently murky, topic. I know nothing of such traffic within the Third Reich in Europe between 1940 and 1945, but have some knowledge of what happened to German intellectual property in Britain and the USA. It would appear that 'transfer' did not necessarily mean that the patents were sequestered and 'given' to others - there were certain responsibilities imposed, and rights to compensation attached to at least some of such transfers.

 

It may - and I emphasise 'may' - be that if Leitz acquired the patent they then made some form of payment. But, perhaps more likely given the circumstances, they may have been 'issued' with the patent by the relevant department of the state for the anticipated benefits of the state rather than for the firm. The practice in Britain and the USA was essentially to identify what enemy patents would benefit the war economy and either direct them to particular companies or invite offers of interest from the firms making up relevant industries.

 

I wonder if the pre-1945 business records of Leitz have survived? There would probably lie the answer . . . 

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That's a little and intriguing piece of history.... when considered it in the context of the  honest and proactive attitude towards Jewish people that Leitz demonstarted in those years (the famous "freedom train")...It is quite some time ago that I was digging  around in this stuff, just out of interest whils studying in Delft. 

It is a very long time ago that I was dabbling in such stuff out of interest, but fortunately there are entries nowadays in Wikipedia that document the corporate history of Oude Delft to jog my memory.

 

It is unlikely that Leitz  themselves had any say in the matter, or even knew, presupposing that speculation is indeed fact. The general plundering of Jewish assets was organized centrally.

However, the first coated lenses by Leitz were for military use, so it is more than likely that they were told to.

 

The Old Delft factory was not closed but ownership was transferred.. Frits Philips managed to protect the business and probably the owners and was on the board of Directors after the war.

Whether this was out of altruism or to protect his supplier of optical parts is unknown, possibly a combination of both.

There were several resistance groups operating from a base quite close to the factory as well.

 

The original Delfineren process, and indeed lens production, was reintroduced surprisingly quickly after the war.

As we know, the  similar  process of restoring stolen Jewish art is still unfinished, seventy years later, and this is far more obscure.

I would say Oscar van Leer was a lucky man.

He emigrated to the USA in 1945, leaving the running of the company to his partner Prof. Brouwer, returning a few years later to become a professor at Delft Technical University. The company became one of the main suppliers of infrared binoculars to the US army during the Vietnam war.

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Is there an enterprise where the glass from old lenses, that have been expertly dismounted, can be sent to for coating?

I have some old lenses and a Leica specialist, who could take the glass elements out and afterwards put them back in and recalibrate my old lenses.

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I think Malcolm Taylor can coat lenses, he offered to do my Elmar 50/3.5 when he overhauled it a few years ago.

I decided to leave it uncoated so as to have the full 1938 experience! And compare with my Elmar 50/2.8

 

Gerry

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I am too superficial an "expert" for a detailed answer, and a lot has been lost in the convoluted company history.

As far as I am aware it was a chemical process which was said at the time to "increase iridescence"  on the glass surface.

Maybe Jan can tell us more.

Sorry no. One of these lenses was in our department. A very heavy product for professional use at a fixed distance, even without an iris (I remember). The name of the lens "Rayxar" reflects the use for x-ray, I think.

 

I was in the prototype department  (proefveld). There was a new method to protect the photomultiplier tube against too much light, giving a too high current.

Some artificial light was sent to the tube during the preparation phase of the exposure, to keep the current down..

I found out, that the glass surface of the tube reflected some of this light to the film. A light grey rectangular field came into the exposure at the upper part of the chest of the patient. That could not be tolerated.

We gave the thing back to the development department. Their idea was to solve the problem by polarizing the artificial light. 

 

Interesting was, that there were no artificial patient in 1961. At first I prepared a cardboard with different objects and finally I gave my chest as a test object.

 

Wasn´t there  problem with Oude Delft selling night vision equipment to Iran or Iraq?

Jan

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Jaap,

 

Rather than "Prof. Brouwer", do you mean Prof. Albert Bouwers? 

 

Bouwers made significant contributions to wide field telescope designs while at Olde Delft Optical.  He is the first to patent the catadioptric meniscus telescope design.  Maksutov and Schmidt Cassegrain designs came later.  He built his prototype in 1940.

 

 

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Sorry no. One of these lenses was in our department. A very heavy product for professional use at a fixed distance, even without an iris (I remember). The name of the lens "Rayxar" reflects the use for x-ray, I think.

 

I was in the prototype department  (proefveld). There was a new method to protect the photomultiplier tube against too much light, giving a too high current.

Some artificial light was sent to the tube during the preparation phase of the exposure, to keep the current down..

I found out, that the glass surface of the tube reflected some of this light to the film. A light grey rectangular field came into the exposure at the upper part of the chest of the patient. That could not be tolerated.

We gave the thing back to the development department. Their idea was to solve the problem by polarizing the artificial light. 

 

Interesting was, that there were no artificial patient in 1961. At first I prepared a cardboard with different objects and finally I gave my chest as a test object.

 

Wasn´t there  problem with Oude Delft selling night vision equipment to Iran or Iraq?

Jan

A well-known Leica specialist (Claus Reinhardt) remarked to me, that he took several lenses apart for a customer of his and the customer himself shipped the glass elements to the Netherlands for being refurbished. After that said customer returned the glass elements to him and he built the lenses back together again. Do you have any information about the company, that did that? Mr. Reinhardt unfortunatelly has no knowledge where the glass went to.  

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I wouldn't know offhand. Arax in Kiev used to do that, but I think they do not do so any more. There seem to be one or two in the USA that still recoat lenses.

Will van Manen tells me that he advises against recoating as the result of simply removing the coating is usually better. Coating can be removed with household vinegar. If you dislike the smell, use Rosemary scented vinegar (seriously)

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