Where is definitive info about lens coatings on different lenses?

Does anyone know of a definitive site with information about the lens coatings used by different manufacturers?

I have a variety of lenses, and they have a variety of lens coatings..
Older lenses have yellow or blue coatings, while newer lenses have purple or green.
Was the color just a gimmik? Why did they not have perfectly clear coatings?

Are some coatings better than others?
Which manufacturers skimped on their coatings or had uncoated internal elements?

Good question. But overriding that is the question of what the condition is of any lens you're bound to get your hands on. It seems miracle enough to get a lens without "cleaning marks". Coatings on used lenses are now a distant second in finding good lenses.
The coating color is just an iridescent lighting effect of the various compounds used to coat the lens. I notice most of the Nikon lenses of latter years to favor a lot of green, for instance. But it's only because of the various methods and compounds they found in their R&D. The actual coating actually are perfectly clear--just like a soap bubble.
To my knowledge all surfaces had at least one coating, after the era of coating began. I am no expert. Just wait for someone come along and correct me. That would be fine. Till then, my answer is reasonably good for boob purposes.

Not all newer lenses look purple or green. Some look predominantly gold or magenta,for example.
If you look at a reflection of a bright light on any multicoated lens, you will see multiple reflections of different colors, though one may seem to predominate. Those colors correspond to wavelengths or combinations of wavelengths of light reflected back by the coating layers on the lenses. The layers, by property of their specific thickness, reduce reflections in a range of wavelengths, and light outside that range will be reflected to a greater degree, giving the color. As already stated, the coatings have no actual color.
Manufacturers sometimes tweak their coatings, too. I have optically identical Pentax "A" and "M" lenses which show different predominant colors.

I remember one guy over on P.nut who wrote very authoritatively and at length on the subject of coatings, explaining that dyes were introduced to balance color rendering of the lens. He also once said the focal length of a lens could be measured directly from the surface of the rearmost element. He got quite snippy when challenged on his claims. Guys like that don't seem to last very long here.

Not sure if there's a definitive list, there's been so many manufacturers over the years it would be almost impossible, and huge.
Example, take a look at how many lenses are on the list of (almost) all m42 lenses ever made. Some of those lenses used the same coatings, like all from the same factory. But some might have had coatings upgrades along their life. Then think about all non-m42 lenses: Nikons, Canons, OMs, Rangefinders, Large Formats.
That would surely be one massive list.

I'm of the same opinion as mentioned above, how any lens has been treated since leaving the factory influences its performance more than how it left the factory. That said, it's nice to know the maximum performance you can get if it's been treated perfectly since it left the factory.

For a bit of history though, check out Roger's Blog Here, if you don't read his blog you should (unless you don't have hours to waste like me).

Hello,
I think that the manufacturers consider this as their secret.

+1

I believe the coatings help contribute to the signature of each manufacturer's lenses; i.e. T* — it's one of the ways they separate themselves from their competitors.

jochen said:

Hello,
I think that the manufacturers consider this as their secret.

Click to expand...

darinwc said:

Does anyone know of a definitive site with information about the lens coatings used by different manufacturers?

I have a variety of lenses, and they have a variety of lens coatings..
Older lenses have yellow or blue coatings, while newer lenses have purple or green.
Was the color just a gimmik? Why did they not have perfectly clear coatings?

Are some coatings better than others?
Which manufacturers skimped on their coatings or had uncoated internal elements?

Click to expand...

The yellow or blue coatings are usually single coatings, the purple/green coatings are usually multicoatings. The coating layer(s) are clear to transmitted light, the colors appear only in reflected light due to constructive interference, the same phenomenon resposible for the raindow hues on a CD, and the colors seen when a thin film of oil floats on water. The actual color depends upon the thickness of the coating, not the material used. The substanc(es) used to coat lenses must have an appropriate refactive index for the glass being coated, as well.

http://en.wikipedia.org/wiki/Interference_(wave_propagation)

http://en.wikipedia.org/wiki/Anti-reflective_coating

Read the links. It's pretty simple on a qualitative level.