Difference between today's Coating and the newer lenses?

[hk300]

I am wondering, if there is any good read on the lens coating.

To what i have heard - please correct me if i am wrong - the main purpose of the coating is to eliminate reflection.

From a image quality perspective, what is the difference between the newer lenses, let's say the Canon EF lenses and the older MF lenses, such as the Canon FD, Russian, Jena, Nikkor AI, ... ?

Also, what is the difference between the coating on lenses compared to the coating on the glass of our spectactors?

Can anyone shed some more information?

[Nesster]

I'm not sure how much coatings have improved from the break-through Pentax SMC. I'm sure they have in some ways.

But here's an illustration of SMC vs. regular pre-SMC coating on the 'same' lens:

[Attila]

Nice set!

[no-X]

As for M42 I have tested, only SMC from Asahi is competitive to present-day products.

Coating was originally intended to reduce reflections, boost contrast and light transmittance. For new digital sensor there is one more purpose: to reduce reflections between sensor and glass surfaces of back lens elements. These reflections can create glare/glow effects, double imaging effects, reduce contrast locally, or reduce sharpness. This wasn't a problem on film cameras, so many older MC lenses have only basic coating on their rear elements, which is sufficient for film, but insufficient for digital sensors (some sensors are more prone to this reflections, some less).

examples:



Letters are quite sharp, but they are surrounded by a kind of glare, which is caused by reflections between sensor and rear glass elements. Similar (but better) situation:



Both taken by wide-opened lenses. Many lenses don't suffer from this kind of reflections from f/4, almost all (even single-coated or uncoated) are perfect at f/8. SMC Takumars are often OK at f/2 or wide-open. It seems that Asahi applied their unique 7-layer MC even on rear glass elements.

[hk300]

So, in theory ... recoating the rear lens elements (using nowadays recoating technology) would reduce the glare if used on a digital body?

[martinsmith99]

In another thread I reported how a bunch of M42 lenses metered a subject at F4.8. My modern Sigma read the same subject as F7.1. I will test further.

If this turns out to be true then there is little point in buying old fast primes if you're after the speed.

[the_Suede]

If you still want a good simple explanation, here's one that perhaps fits the bill:

http://www.edmundoptics.com/techSupport/DisplayArticle.cfm?articleid=247

There is no "easy" way to explain AR coatings, so please bear with the maths...
The main difference between coating on glasses and coatings on camera lenses is the numbers of layers of coatings and how hard the outer surface can get. Many coatings for glasses are also specifically engineered to repel water deposits and dirt in general, rather than to provide the best AR possible. A rather sound way to approach the subject I think...