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

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.

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

Conclusion

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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