I am currently looking for a Summicron M28 ASPH lens. When I look around, I noticed that the color of lens coating varies a little bit lens by lens. I am not sure if this is normal case or it just appears different but actually the same for every lens. Any advice on this? Thanks

-- Michael Li (michael6609@hotmail.com), February 16, 2002

Answers

Yes. I believe that since Leica matches the coatings (or lack thereof) to the particular properties of the glass (eg., the index of refraction, which affects reflectance), it is not surprising that coatings appear slightly different for different lenses. This is true today as it was in the past.

Not only that, but I have noticed variatons in the apperance of the coating (color) in lenses of the same type of similar vintage. I can't say whether this reflects factory variations, changes in coating technology, or the fact that the lens surface was damaged and then repolished and coated.

One thing I can say is that there are general trends you will notice after looking at many Leitz/Leica lenses over the years.

1. Pre-war lenses - no coating unless sent back to the factory for coating post war.

2. Early post war coatings - very bluish (as was the color rendition of the lenses, except for the famous "yellow glass" collapsible Summicron, the yellow glass color neutralizing the blue coating.

3. Mid-late 50s, more violaceous color of coating.

4. Later lenses, 60s or so, violaceous with reddish and yellowish coloration added.

5. Current lenses. I have noticed in the newest generation of lenses that in addition to other colors, there is a substantial greenish hue, especially in some WAs, like 24/2.8 Elmarit. This may well be related to glass selection for these lenses.

-- Eliot (erosen@lij.edu), February 16, 2002.

Hi, Eliot

Thanks for the advice.

-- Michael Li (Michael6609@hotmail.com), February 16, 2002.

Hello Michael. Over the years,Leica have been very serious and careful with lens' coating in reducing flare and maximising color fidelity.

They have not piled on multi coating merely to give the lens a glamorous effect, indeed I think they take a more conservative approach than other manufacturers. An example is in the 135mm Tele Elmar M f4 .. a lens with brilliant color fidelity but requiring no more than single lens coating to achieve it's results. Regards.

-- Sheridan Zantis (albada60@hotmail.com), February 17, 2002.

"2. Early post war coatings - very bluish (as was the color rendition of the lenses, except for the famous "yellow glass" collapsible Summicron, the yellow glass color neutralizing the blue coating."

Can we be sure the glass is yellow? It may look that way by transmitted light. Review my post on the transmitted color of the various 50mm Summicrons.

Blue and yellow are split-complements. If the coating reflects blue, then blue is being subtracted from the transmitted light. That leaves more yellow to be transmitted. (Subtracting blue leaves red and green, which together are perceived as yellow.)

SO is it the glass that's yellow, or the subtractive effect of the blue coating?

-- Bob Fleischman (RFXMAIL@prodigy.net), February 17, 2002.

Bob. I always thought the glass (a variant of Crown lantanum glass with radioactive [uranium] impurities was actually yellow. Sure yellow is the complement of blue, but if this were the explanation, all early Summicrons and all early post war lenses would appear yellow. But this isn't the case, only a small fraction of early Summicrons and none of the other lenses appear yellow.

-- Eliot (erosen@lij.edu), February 17, 2002.