Air bubble occlusions in Kodak Commercial Ektar 10" lens elements

[FLC]

Acquired a Kodak Commercial Ektar 10" lens (mfr. 1957) for my Toyo 4X5 view camera and, upon delivery and inspection, two air bubble occlusions are found in the lens elements.

One air bubble occlusion is in the front element; the second air bubble occlusion is in the rear element. The bubbles are about the size of a champagne bubble: Very small, but immediately observable within the composition of the lens glass when viewed looking through the glass from both the rear and front objectives.

Questions:

1) Will these occlusions affect resolution, contrast, and image quality?

2) How could this lens pass Kodak quality control at the time of manufacture and distribution? I have read that Kodak Ektars are among the finest lenses of their era.

3) Is it common to find minute bubble occlusions in Kodak Commercial Ektars?

Thanks in advance for your comments.

[BarryS]

1) No

2) See #1

3) Yes

[Vaughn]

The bubbles are found in the best of the old glass. In fact, I think it was a sign of good quality glass -- or something like that. Nothing to fret at all about.

[Mark Sampson]

I believe that at one time small bubbles "were a sign of quality glass", and that Nikon was the first optical company to produce bubble-free optical glass, but I have no sources for either statement. I will say that I have owned and used many Kodak Ektar lenses, and all of them were/are of excellent quality.

[Don Dudenbostel]

The old timers claimed bubbles indicated a premium lens. A friend of mine who passed away in 1984 at 102 years old was a photographer from the early years of the 20th century and he claimed bubbles in the glass indicated the best glass. I've owned a number of lenses with bubbles. If you use a high power magnifier like a jewlers loupe to examine the glass you'll see tons of tiny bubbles. Its just a part of making glass.

[Steven Tribe]

I am sure the air bubble/quality glass is a myth - spread around by the makers of the "new glass" in the 90's to explain away their problem with air bubbles. They were constantly changing their glass formulae in the search for different refractive indexes and were more concerned about surface weathering of the new creations rather than a few obvious air bubbles.
In a sense, it is true. More bubbles than usual, means experimental glass, newly developed optical solutions and higher original purchase price.
A few, or even a whole cascade of, air bubbles will not make any difference.

[GPS]

I am sure the air bubble/quality glass is a myth - spread around by the makers of the "new glass" in the 90's to explain away their problem with air bubbles.
...

It is not a myth but a reality well explained at www.zeisscamera.com (go to Services - Overhauling a Contax IIA -IIIA Body - and read the whole explanation there).

[Kevin Crisp]

When GM was having persistent problems with its engines knocking it began calling the annoying sound "the sound of economy." People were supposed to start appreciating it.

As the Car Talk guys said, there is a special place in hell for whoever thought that up.

[Peter Gomena]

My 21-year-old Toyota pickup knocks all the time unless I run it on premium gas. I call it the sound of ethanol.

Peter Gomena

[goamules]

My son's Mazda knocks badly. I think it was made in Jena and the tank has bubbles in it.

[Steven Tribe]

"It is not a myth but a reality well explained at www.zeisscamera.com (go to Services - Overhauling a Contax IIA -IIIA Body - and read the whole explanation there)."

Well GPS I have read the section, which has useful paragraphs but others which are misleading (the fungus section, for instance).
Even if the remarks about high quality glass requiring higher smelt temperatures are correct, there are a couple of problems in the argument he gives. The loss of air bubbles is not related to the molten glass' temperature directly - but to the absolute viscosity of the glass at a given temperature. This temperature/viscocity relationship will be different for the type of glass being made. I am sure that the "new technology" talked about is some kind of centrifuge which will quickly "lift" the bubbles out of the molten glass rather than some refractory development.

To say that a lens with air bubbles is better than a lens without is obviously nonsense when they have the same glass formula. But makers will never admit it as the fact that they can, on a good day, make glass completely free of bubbles, would make buyers insist on a price differential. I am sure that the cast glass blocks always have some sections which are completely free of bubbles. It is a question of the waste percentage that Zeiss etc. are prepared to accept for each glass block.

[GPS]

I agree with you that some of his arguments are not correct (see his ideas about cleaning lenses!) but the explanation of the better/worse glass for lenses is not his own. He surely got it from manufacturing sources. But there is no need to twist his arguments - he relates the lack or the presence of bubbles to the time needed for them to get from the thick viscous molten glass at given temperatures and the capacity of crucibles to hold it sufficiently long. Seems logical enough to me.
Also, to say that today's glass is free of bubbles because manufacturers had good days while making it seems not serious enough. ;-)

[Lynn Jones]

Hi FLC

All optical glasses had bubbles due to the mixture of sands and chemicals. This changed well into the 1950's when certain Japanese companies started to remelt and mix using platinum coated mixing vessels and mixers. After that, most optical glasses used that technique to prevent bubbling. It didn't really matter, no testing ever showed the difference, it was always just cosmetic.

Lynn