Difference between single and multicoating.

What about the difference in quality, between single and multicoating? And

one more question.

How can we see which is which. Ie. how we can see if a lens belongs to the

first, or the second class?

The optical performance (resolution) of a lens should not be influenced by the coating. However, its resistance to flare depends on the coating, besides optical construction, beeing the multicoated less affected by light sources or extense bright areas. Nevertheless, you will have less flare using an appropiate hood (or your hand) to shadow a single-coated lens than using a multicoated lens whithout protection. Theoretically, the best results would be obtained with a hooded multi coated lens, but I observe little difference respect a well hooded single coated, although others can disagree.

The former Nikkor lenses are single-coated, whereas all AiS, Ai and AF lenses are multicoated. Some pre-Ai lenses are also multicoated, or have some elements single-coated and some elements multi-coated. Pre-Ai lenses designated "letter"?C (O?C, P?C, H?C, ...) and those with rubber focus ring are also multicoated.

Tipically, multicoated Nikkors show a green or orange hue when observed under a light at a certain angle, whereas ingle-coated have a bluish color.

Finally, I would say that some people still prefer single coated lenses, at least in some situations, for the "retro" look, or the "glow" that they give to the pictures, in opposite to the technical, high contrast appearance of modern multicoated lense. As an example, Cosina-Voigtlander currently produces 2 versions of their 40mm f1.4 in leica mount, one single coated and the other multicoated.

It's not a hard and fast rule, but single coatings are likely to be mostly yellow and violet, while multicoatings are more interesting, green, blue, red, and pink.

The quality difference can be substantial. Multicoating reduces flare and ghosting and improves contrast. The more complex the lens, the easier this to see. Zooms (lots of elements) and wides (strongly curved elements) show the benefits of multicoating most clearly.

And, as an aside, multicoating actually does increase resolution, at least when resolution is measured by a MTF (modulation transfer function) test. The coating increases contrast, and that increases the amplitude of "modulation" (the difference between light and dark on the MFT chart pattern), so you can have a slightly higher resolution before modulation falls below a critical threshold. The "visible resolution" is higher.

Multicoating is an anti reflective coating used in many areas of optics. A certain percentage of light reflects off the front surface of glass. Multicoating is a series of thin (1 to 1/2 nanometer) thick metal coatings that disallow reflections as light can only travel through a medium on a full wavelenth. As very little light is reflected off the surface, more is travelling through, so therefore, a clearer, more defined image is available.

Single coated lenses, once again in optics, offers nothing more than some sort of scratch resistance.

The only difference in the coloured bloom of the coating is the types of metals used in the process, and hasn't anything to do with the number of coatings.

I would like to see a "single" coated lens. It shouldn't exist in a glass world.

"Single" or "multi" refers to the number of layers of the coating on a particular glass

surface. I don't know why David thinks single-coated lenses don't exist. They were all

that existed from roughly 1940 to roughly 1970.

Single coatings on photographic lenses are typically applied for the purposes of their anti-

reflection properties. The most commonly used material for single coatings is magnesium

fluoride. In my experience, the most common color cast is blueish. A single coating can

reduce the refelection at each air/glass surface from approximately 4% to about 1.5%.

There is a brief article at http://en.wikipedia.org/wiki/Anti-reflective_coating; an excellent

but more technical article starts at http://www.mellesgriot.com/products/optics/

oc_1.htm. The second article continues over a series of pages, extending to multicoating.

Single coatings are based on destructive interferrence and should be one quarter

wavelength thick. One reason that they aren't perfect for photography is that they can't

be exactly one quarter wavelength thick for all visible wavelengths. By using many layers,

the coating can be tuned to operate better over the entire visible range, and to have

increased transmission.

The practical effect? It depends. On a simple lens, with few air/glass interfaces, the

difference between single and multicoating will rarely be important. On a zoom lens it

with many air/glass surfaces, it will make a bigger difference. To many refections from

many surfaces can lower contrast.

How to identify the coating? Multicoatings typically have more chromatic colors, and a

single lens may have several different colors on different glass elements. The reflected

color comes from the design of the multicoating (number of layers, materials, thicknesses,

etc.) -- no multicoating has perfectly flat transmission across the visble band, so there will

be some color cast to the reflected light. If you reflect a light bulb off of bare glass, a

single-coated filter, and a multi-coated filter, you can tell the difference in the intensity of

the reflection. But without experience looking at examples, probably the easiest way is to

look up a particular lens.