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Coating color differences


Csacwp

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Short answer - I've never seen a 90mm APO-Summicron with "orange" coating. Are you sure you are not confusing the APO-Summicron 90 with the previous (1980-98) non-APO Summicron 90mm - which has a nearly identical barrel size and shape? The immediate visible difference being the non-APO has engraving on the front around the glass, while the APO has engraving on the side of the lens hood/barrel?

 

APO - https://i1.wp.com/digitalphotographylive.com/wp-content/uploads/2015/05/Leica-Apo-Summicron-M-90mm-f2-ASPH-Lens-05.jpg

non-APO - https://jonasraskphotography.files.wordpress.com/2015/03/dscf56161.jpg?w=1620

 

There are definitely sometimes coating "color" differences between those - but the coatings' affect on image quality will be virtually irrlevant compared to the fact that they are completely different lens designs in the first place. Like comparing an orange 1980 Ferrari to a blue/purple 1998 Ferrari.

 

Extended answer: Just for the record - lens coatings don't have "colors." They are colorless transparent compounds, coated a few molecules thick on the glass. Often magnesium fluoride (not to be confused with "fluorite" lenses themselves).

 

But - what they do is reduce reflections by "destructive interference" - a thin coating on the order of 1/4 the wavelength of light produces TWO reflections of light, one from the glass, and one from the coating surface above it. Which end up "out of phase" in the wave model of light, and thus cancel each other out, resulting in NO reflection. Usually with ONE wavelength (color) sneaking through as a visible color, depending on the coating structure (how many layers, which wavelengths are affected).

 

https://upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Optical-coating-2.png/220px-Optical-coating-2.png

 

The exact same principle that produces "colors" from the thin colorless surfaces of soap bubbles or oil slicks on a wet pavement. Which, you will note, produce the same range of intense (monochromatic) yellows, oranges, blues, greens etc. as lens coatings.

 

http://www.waynesthisandthat.com/images/gbheader.jpg

http://www.gadha.org/images/20090813211248_oil-rain.jpg

 

A key point is that lens coatings do not affect the color of transmitted light (the light that gets through the lens to make the picture). Only the reflected light, which is either cancelled out altogether, or reflected back towards the subject.

 

If any reflections are severe and bright enough, as in this extreme example of lens flare, the selective colors produced by the coatings will tint the flare spots that are produced by internal lens reflections - thus you get pink or green flare circles from reflections from glass coated to only reflect pink or green (and destroy the other colors).

 

https://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/CCTV_Lens_flare.jpg/220px-CCTV_Lens_flare.jpg

 

That is about the only "image quality" effect that coating color might produce - assuming the coatings are high-quality and correctly produced and "fit for purpose."

Edited by adan
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The pre ~2012 Apo-Summicron 90s have a  coating that makes the front element look orange... same look as the pre-Apo Summicron, the 75 Summilux, etc.  The newest Apo-Summicron 90s have a coating that gives the front element an irredecent purple-blue-green kind of color that is quite different.  I have confirmed this by comparing multiple examples of the Apo in-hand.  The newer ones have front elements that are the same color as the ones on the 50mm Apo-Summicrons.

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Hello Csacwp,

 

Welcome to the Forum.

 

The earlier lenses that are coated with purple & brown coatings are from a time period when fewer layers of ant-reflective coating were applied. 

 

Coating combinations that include green layers are indicative of multi-coated surfaces where there are a greater number of different layers, including inert clear layers.

 

Leitz was 1 of the earlier utilizers of multi-coating in the 1970's, altho these multi-coated surfaces were mostly on military optics.

 

When asked at that time why they were not mult-coating their civilian optics they said that they saw little advantage in multi-coating small numbers of lens elements that were made using high refractive index glass, with relatively gently curved surfaces,

 

They said that they preferred to use what they called "staggered" coating. Each lens having the number of layers that were optimal for that glass type & that specific surface curve.

 

Instead of putting a large number of layers on each surface regardless of circumstance.

 

Leitz also said that multi-coating was more useful on lenses with steeper curves made out of lower refractive index glass.

 

Best Regards,

 

Michael

Edited by Michael Geschlecht
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By chance, my local shop has an older (2002) 90mm APO-Summicron in the case. Shot this picture of the reflections - blue on the front element, greenish from the middle elements, and yes, orange-yellow from the rear two elements (the concave ones behind the aperture blades). I don't know if that is the "staggered" coating Michael means - 2002 is "recent" by Leica timelines.

 

Sorry about the lack of focus - my arms are not 0.7 meters long. ;)

 

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

 

Anyway - I still doubt small coating differences will make a noticable change in image quality. More important with the fast teles (in my experience) is getting a lens that has been to Germany recently - since the new factory opened. I have noticed even rather OLD lenses that have been upgraded to 6-bit coding (e.g. 75 Summilux, 135 APO-Telyt) tend to show somewhat higher consistency in focus and general resolution (on average), probably simply because they've been reassembled and checked to Leica's most recent specs (not because of the coding per se).

 

But if you want to use coating colors as a way to identify newer, post-2012 lenses, I guess that works.

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Hello Andy,

 

I am not sure "which" color layer is for "what".

 

In the 1970's there were already multi-coated lenses with 17 layers.

 

Some layers were to reduce reflection. Some layers were clear spacers.

 

Some layers were to adjust color cast so that different types of glasses with different characteristics would end up creating a uniform "warmth" or "coolness" within a line of lenses.

 

Best Regards,

 

Michael

Edited by Michael Geschlecht
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