View Full Version : Ektar coating reflections

Mark Erickson
26-Apr-2004, 10:30
Here's a fun post for the Ektar afficionados among us. I picked up a Kodak Medalist with an Ektar made in 1945. This lens is a Heliar formula 100mm F3.5 and does not have a (L) mark on it. As I understand it, the (L) indicates that a lens was hard-coated on all surfaces using a vacuum process. Prior to this, Kodak lenses were either uncoated or soft-coated on their interior surfaces only. Now, it is possible that Kodak shipped some hard-coated lenses without the (L) mark, but I haven't seen any definitive evidence on the web as to whether or not this happened. In addition, I understand that there were 3rd party companies that hard-coated lenses in the aftermarket.

People talk about identifying coatings from the color and intensity of lens reflections, so I decided to do an experiment and take pictures of lens reflections using a digital camera. I used a halogen desk lamp in a darkened room and took the pictures with a Canon S10 camera with the white balance locked down to daylight and exposure compensation at -2. I took pictures of the above-mentioned 1945 100mm F3.5 Ektar, a 1947 105mm F3.7 Ektar, a 1947 152mm F4.5 Ektar, and a 1952 203mm F7.7 Ektar. The color temperature of the desklamp is definitely on the warm side, but I think that a side-by-side coating comparison can be made from them. The results are summarized in this JPEG image (http://www.westerickson.net/mark/misc/fourektars.jpg).

A couple of things are worth pointing out, I think. When I evaluated the 1945-vintage Ektar, I expected to see two really bright reflections from uncoated outer lens surfaces and a collection of much dimmer reflections from soft-coated inner surfaces. What I saw instead was a complete set of muted, amber-colored reflections. It looks to me as though all surfaces, including the outer ones, have coatings with the same thickness. The 1947-vintage 105mm and 152mm lenses both display similar mixes of purplish and magenta reflections. A real surprise to me was the 1952-vintage 203mm F7.7 lens. I was expecting a mix of purplish and magenta reflections like those of the 1947-vintage lenses. All of its reflections are a complete set of muted, amber-colored reflections much like those on the 1945-vintage lens.

What does it all mean? I don't know. Anyone have any thoughts?

Michael S. Briggs
26-Apr-2004, 11:48
In that era the most likely coating is a single coating of Magnesium Fluoride. The color cast of the reflection will depend on the thickness of the coating. Thickness variations could be intentional, or might be from manufacturing variations due to limitations of the technology of that time. Kodak did use hard coatings without using the circle-L symbol, e.g., the Aero-Ektars produced for the military.