A piece of history: Air Ministry Ross Xpres 5 Inch f4 Lens

Another project I am preparing for some time is related to large format photography so I was planning to buy an old lens for experimentation. Looking through a huge toolbox-turned-dumpster of a late aunt of mine I discovered, to my surprise an old jewel: a Ross 5in Wide Angle Express f4 with A(crown)M markings, meaning it was an Air Ministry lens (aka used in WWII reconnaissance aircraft).

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The lens was, well, terribly dirty… So I got my good-old set of screwdrivers and pulled everything apart. I washed the elements well under running warm water to get rid of the dirt in every little corner and then cleaned all glass with Zeiss liquid. I left them dry for a couple of days under the sun.

Drying lenses under the sun is a joy, isn’t it. The aperture module was also dirty and sticky so I soaked it in warm water and opened/closed it a few times to have the blades move freely and get rid of the dirt. I then dried it well with a hairdryer and let it dry in the sun as well. There was also a yellow gel inside the lens which I wanted to get rid of anyway. The only thing that still gives me trouble is the small lock screws for the threadings of the front and back elements. These must have been threaded after the assembly and tolerance is very small. Once the lens was disassembled it is not possible any more to realign the upper and lower half of the lock screw threads. The lens is stable and tight but for some microns they will not align… maybe I need to heat the barrel a bit.

Despite the incredible filth all optical elements turned out to be in pristine condition and now I have a brilliant new historical lens for my project! I just wish I knew more on the history of this lens.

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