There are quite a few versions of the coveted Kodak Aero Ektar lenses. Here are the two most common versions: The 12" f2.5, weighing 7.3 Kg/16.1 lbs is on the left. It sports two dots, one yellow, one purple, and was made in 1953. Perhaps it was used to spy on Iron Curtain countries during the Cold War.
In the center is the much more common f2.5 7" version, with a weight of 1.45 Kg/3.2lbs. There are lots of these around from WWII. This example was made in 1944, about three years after Aero Ektar inventor George Aklin's 1941 patent.
To the right is a far rarer, and more desirable Aero Ektar with a very much slimmed down mount as supplied by Kodak in 1951, making it one of the later versions of this useful lens. It weights a "mere" 1.2 Kg/2.8 lbs, and has a slim aperture ring, a much slimmer front hood with the indicia placed at the periphery, and appears to have a hard coating. This also sports the two dots, one yellow, the other purple. It has a manufacturing date of 1950.
These were very expensive to produce. Kodak took a great deal of pride in the Ektar lenses, and today they are still among the sharpest. Our masthead of the Charles River and trees was shot on Type 55 using an Ektar lens, and you can view it with a microscope and see every leaf, so sharp it is.
All of these are quite well made and thick lenses of the double Gauss design, with rear elements comprised of mildly radioactive thorium glass that, over time, produces color centers at the molecular level responsible for producing a reversible yellowish or even brown cast to that element. The physics of color centers has been studied in crystals and other optical substances and this sub-micron change to the actual structure of the molecules can be brought on by gamma radiation and reversed by exposure to UV. Read Micheal Brigg's emphatic, and excellent treatise on Aero Ektar radioactivity.
The lenses shown are of the same design, just scaled up (or down) depending on the focal length. There are other longer and shorter focal length Aero Ektars too, including a 6" f2.5 version, and slower, longer versions that are not often much sought after, but show up on ebay frequently.
People love the mysterious dots, so here is more about the dots, here, and even more here.
Even more from Aero Ektar inventor, George H Aklin....Click Here
|Aero Ektar Patent|