Coating colour question?

[Shen45]

I recently purchased two absolutely beautiful commercial Ektar lenses dated sometime in 1947 [ES] and both of these lenses have a very distinct "blue" coating appearance. I also have a 12" Commercial Ektar in a barrel - again sometime in 1947- but a later production due to the higher number after the ES. This Ektar has a very different coloured coating, it is a brown/yellow/purpleish colour when viewed straight into the lens.

All lenses are luminised with the L in the circle. Images are identical no matter which lenses is used so I was wondering if anyone has any thoughts. I'm referring to black and white images. Contrast and sharpness are the same for all lenses.

One of the lenses is marked ES 180 whereas the other the serial # is ES 630

Just a curiosity someone may have a thought on.

[Craig Tuffin]

I think they are ALL broken Steve...better send em up here to me :p

[Robert Perrin]

Steve, my recollection is that the early lense coatings were blue. I've only one commercial Ektar, an 8.5" with an RA number; it's coating is purple as is the 127mm Ektar that I bought in 1953. I'd surmise that your lenses spanned the change from the early coating to later formulas.

[Shen45]

Hi Craig :) the lenses would survive the trauma of going to Queensland and I agree with you Robert that the lenses are probably very early on in the Kodak coating regime. I had heard that the earlier coatings were/are softer. If that is the case these have had a very privileged life in their 63 years as there is not a single mark on them anywhere.

[tbeaman]

I've driven myself crazy with this kind of thing before. I purchased a 90mm Leitmeyr a while back that had a distinctly blue/cyan cast in 3/4 reflections, but wasn't marked with an 'o' to indicate coating. I had only ever seen purple/amber reflections in single coated lenses before, and my Kodak Anastigmat from the '20's had a much more subtle but still obviously cyan reflection in one element, so it was maddeningly confusing.

I actually eventually bought another 90mm Leitmeyr with the 'o' marking just to compare, and while the latter one's reflections are a little more purple, they're fairly similar. No obvious conclusions, but I'm leaning towards believing the first has an earlier version of coating. At some point, I'll do some image tests to confirm.

[Peter K]

The hue of the coating depends not only on the thickness of the layer itself but also on the refractive index of the glass below the coating. And of course the refractive index of the layer e. g. Lithiumfluoride together with the incident angle of the light.

In any case a more bluish or more amber hue has only a little influence if slide-film is exposed with such a lens but not on the contrast or transmission resp. exposure-time.

Peter

[Lynn Jones]

Kodak's original lens coating had a yellowish or golden cast, the B&J lenses had a bluish or purplish cast, the multicoated coatingings have lots of different casts, who cares they don't change the color of the image unless this is desired by the manufacturer to correct for another problem.

Some of the "dyed in mass" glass filters were so poorly corrected that they used colored coatings to deliberately correct the color of the glass.

Lynn

[Domingo A. Siliceo]

by chance, I've discovered the front lens of my just acquired Caltar II-E is red ruby, as you can see in attached image.

Just out of curiosity, what the red colour in the coating means?


http://i62.tinypic.com/evc40o.jpg