Bubbles in a sonnar lens
Mods, DIY & Lens Adapting Tutorials & Guides

The Impact of Air Bubbles in the Optics of Old Lenses – By Jordi Fradera

July 2, 2020

Tell me something that is heavy, hard, old and almost unbreakable. Is it a stone? No, it’s a prewar Contax. I say “almost unbreakable”, as these poor specimens have seen better days. The general state of both these camera is deplorable, they are missing parts and nothing moves.

The cameras were loaned to me as a curiosity by my friend and ex-professional photographer, Enrique. Their origin is unknown, my friend received them from another professional more than 30 years ago and then they no longer worked even then. A lack of affection and use had caused them to no longer work, so he has had them as decoration in his house.

But whilst the camera’s don’t work, the lenses are only dirty. My curiosity in them caused me to discover something strange about them – whilst inspecting and attempting to clean the lenses, I saw that the 50mm f/1.5 Sonnar lens had air bubbles in the rear group of elements, so I thought I would take some photos to demonstrate how they impacted the results.

Bubbles in the Sonnar

As you can see in the image at the top, the bubbles are evident, one in particular is of “enormous” size. Currently we all seek perfection and we would not accept such a defect but there was a more tolerant or resigned time, for the photos of that time that quality was more than sufficient.

Here you can see some of the bubbles in two of the elements.

Adapting to the Sony

I could not resist the temptation to take photos with the lenses but I only have a Sony A37 camera with a “Flange focal distance” much greater than that of Contax cameras. Therefore I could only take macro photos.

For the adaptation I used a Sony plastic body cover, drilled in such a way to avoid risking scratching the fixed translucent mirror of my Sony A37 – the rear of the 5cm lens was 1mm from the mirror.

The focus is fixed since Contax cameras are equipped with a helical movement system. In the case of my adaptation, the focus is only 360mm.

As you might expect, despite the bubbles, no marks or defects can be observed in most of images.

Bubbles in the Bokeh,

Where the bubbles can be seen is in the bokeh when photos are taken that include out of focus highlights.

Here you can see a comparison of the bubbles in the lens, and the impact of them on the bokeh. On the left is a close up photo of the glass itself, and on the right is an isolated out of focus highlight that I have mirrored and rotated to show how the bubbles


These lenses are not an ideal match for my camera, but they did give me an opportunity to do this test and demonstrate how certain defects in old lenses do and don’t show up in the final photos. My curiosity has been satisfied, I couldn’t sleep without doing these tests. It has been fun and quite laborious. Now I have finished this article I will return the cameras to their owner and they will possibly continue as decoration for many more years…

Thank you for reading

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  • Reply
    Gary Harding
    July 2, 2020 at 4:35 pm

    I have bubbles in my Jupiter 8, I haven’t seen any defects in any of my images either 🙂

  • Reply
    James T
    July 2, 2020 at 5:43 pm

    The folks over at LensRentals found a fly in a lens and before extracting it showed that it had minimal impact on image quality (https://www.lensrentals.com/blog/2019/04/removing-fly-from-weather-sealed-canon-70-200mm/).
    Discreet(ish) objects within a lens generally have much less effect than smears and fingerprints.

  • Reply
    July 2, 2020 at 6:28 pm

    Hello Jordi,
    Your post trigged my curiosity.
    I have a 1937 ContaxII and a matching Sonnar.
    My Sonnar was accidented (fallen I suppose) , comletely out of focus and beyond “reasonably costs” to use.
    I still keep it…in case of.
    My Contax had a good CLA and works well (shutter speeds are accurate (besides that 1/1000 is more 1/800)
    I mounted a 1955 Russian Jupiter8.
    I like the soft way (the “dégradé” in French) the lens goes from sharp to unsharp
    This is a nice lens…with a few air-bubbles.
    They never seemed to affect the pictures I took with it.
    I’ll try to make a picture in highlight, out of focus to see if I can recognise the bubbles.
    With a T-Max100 I should be able to see the difference between the bubbles an the grain 😉
    When I compare this 1955 lens, a copy of the 1930-ies Zeiss lens, to my Fujinon lenses on my digital Fuji’s, I can see that we “speek” an other language now.
    I studied in a film school in Brussels in mid 70, before attending 3 years film we had a year photography.
    3 years ago I reconnected with “half-analog” photography…developping B&W, scanning and processing with Capture One.
    I re-discovered the time to take a picture when you have 36 pics on a roll (or 8 with mij Fuji 6×9)
    Anyway thanks for your article

    • Reply
      Jordi Fradera
      July 3, 2020 at 11:01 am

      Please forgive my English translated with Google first.
      Thank you very much for your comment and also to the other people who have done it.
      I must confess that I have been a simple fan for 65 years and the saying goes: “The devil knows more by old than by devil” and that my means are simple but my patience and curiosity are great. On the other hand, I usually do my “inventions” with things that I have at home, if I were to test a lens with a commercial adapter, I wouldn’t enjoy it as much.

  • Reply
    Kurt Ingham
    July 2, 2020 at 7:28 pm

    I’m glad you had fun, and some nice pix, but this issue (bubbles in glass) was resolved LONG ago. Contax to Sony adapters that focus to infinity are readily available, though you need 2 types -one for 50mm, another for ‘other’ focal lengths

  • Reply
    Kurt Ingham
    July 2, 2020 at 7:30 pm

    I’m glad you had fun, and some nice pix, but this issue (bubbles in glass) was resolved LONG ago. Contax to Sony mirrorless adapters that focus to infinity are readily available, though you need 2 types -one for 50mm, another for ‘other’ focal lengths

  • Reply
    July 2, 2020 at 8:29 pm

    Ha! This is great! Very interesting.

  • Reply
    Kurt Ingham
    July 3, 2020 at 3:22 pm

    Glad you had fun, and some nice pix BUT rf Contaxes are far from unbreakable (quite the opposite) and the issue of bubbles in the glass has been resolved for quite some time

  • Reply
    Kurt Ingham
    July 3, 2020 at 3:24 pm

    sorry to repeat –
    I thought the first comments were an unposted draft

  • Reply
    Martin Andersen
    June 21, 2021 at 6:57 am

    I have an old 1930s era Contax I use for decoration since the mechanism is seized up and I can’t afford a CLA yet (the rusticles under the leather grip is common in old Contax cameras, and a sign of an original). From my research, the ones in best physical condition seized up long ago, hence lack of use and being in good condition, whereas the working ones have been loved to death. Often the problem is due to incorrect or no oil in the clockwork mechanism. Like a watch, they have to be maintained with the right oil; the wrong kind may be too sticky and seize the machinery, and none a similar result.
    There is a few bubbles in some of my lenses, but nothing that worries me or affects the images. Bokeh wasn’t a thing back in the day, a mere side-effect, it’s a more modern aesthetic.

    • Reply
      Jordi Fradera
      June 21, 2021 at 11:16 am

      The cameras in the article were not mine, they were given to me by a friend who had them for decoration. I am not a professional but I have seen many cameras with a viscous fat problem, in front of me I have a PRAKTISIX with that problem.
      Regarding bubbles and bokeh in the article I treated that problem as a curious thing, although I know that it is frequent
      I wanted to see the effect of the bubbles in the bokeh and it was interesting. You already saw the photos of flowers with my invention for Sony A37 without visible defects because of the bubbles.
      There are those who buy that type of old lenses at a high price, ask to 35mmc.com
      Thanks for comment.

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