Do nano coatings actually make a difference?

Question

Nikon famously has "nano coatings" on it's higher ended lens, and many photographers online swear that this visibly improves their images. However, it's not clear what the actual improvement is (aside from reducing flare), and whether or not the effect is simply a confirmation bias of the lens owners, trying to justify the more expensive lens.

Is there any evidence based data on what exactly the contribution of the nano coating to image quality is? I've seen the previous post on this topic, and although it explains what the coating does physically, I have yet to see a detailed comparison of images with and without the nano coating.

Answer 1

This isn't just one company creating their own buzz, and corresponding buzzword, for marketing purposes. This has been an important advance in optics in general over the last 15-20 years. The technology is still in its early phases, where there is a lot of proprietary knowledge being closely held by the companies that develop this.

I suspect it will be difficult to find a lot of A/B comparisons with/without nano-coated lenses. Firstly, because nano-coating (in Nikon parlance, or Subwavelength Structural Coating – SWC – in Canon's parlance) is not simply an add-on option like an underbody coatings in car sales, the availability to the general public is just not there.

However, below are some of the few actual quantifiable claims or visually qualifiably claims I could come across:

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Canon's technical description of SWC technology shows a photo of 2 lenses side-by-side, one with SWC and one without. It's hardly the numerical data you're probably looking for, but taking them at their word, the visual evidence of reduced reflection from one to the other is compelling.

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The abstract of this scientific paper on colloidal subwavelength nanostructures for antireflection optical coatings. by Zhao, Wang, and Mao states that,

The structure is used for antireflection coating, and the measured reflectivity of a glass substrate is reduced to 0.3%. Enhanced transmission through the substrate is also observed.

0.3% lost to reflectivity is just 0.004 stops lost to reflection.

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The abstract of this paper on tuning the peak position of subwavelength silica nanosphere broadband antireflection coatingsby Tao, Hiralai, et al states,

Subwavelength nanostructures are considered as promising building blocks for antireflection and light trapping applications. [...] With a single layer of compact silica nanosphere thin film coated on both sides of a glass, we achieved maximum transmittance of 99% at 560 nm. [...] Such peak-tunable broadband antireflection coating has wide applications in diversified industries such as solar cells, windows, displays and lenses.

Their stated peak transmittance corresponds to a T-stop of 0.014.

Answer 2

The first question would be: "...a difference compared to what?"

Most camera lenses have been multicoated for decades now. Before that (from around the '50s to the '70s) they were single coated. Before that, most were un-coated.

• Uncoated lenses typically lose around 4-8% to reflection.
• Single-coated lenses lose around 2-4% to reflection.
• Multicoated lenses lose around 0.5-1% to reflection.
• Nanocoated/SWC lenses lose around 0.05-0.1% to reflection.

Literature from both Nikon and Canon often compares transmission with their new coatings to transmission of lenses with no coatings at all. Although technically accurate, I find this disingenuous at best, carrying an implication of a much larger improvement over existing technology than is even close to real, by comparing to lens designs from the 1950s (or earlier).

I hasten to add, as well, that achieving a transmittance of 99% isn't exactly new or earth-shaking. Good multicoated lenses have achieved transmittance around 99 to 99.5% for decades now (and there does seem to be a clear trend for improvement over time, so I'd guess current coatings are mostly closer to the top end of that range than the bottom).

In theory, if you applied nanocoating/SWC to every lens element, a design with lots of elements could reduce reflection by quite a large margin. In reality, it's only applied to a few surfaces (e.g., 2 to 4 out of designs with around 11 to 13 elements--and frequently only to one surface of an element).

There are a few potential advantages, such as allowing a lens design that would otherwise produce unacceptable levels of flare/ghosting¹, but would be acceptable with good enough coatings. At least to my knowledge, that's purely theoretical though.

Looking specifically at flare: the lenses to which these coatings are being applied make no sense to me at all. Flare and ghosting are real problems with wide angle primes and (especially) short zooms. The lenses you can get with these coatings are almost exclusively long primes.

At least in my use, even with a 70-200/2.8, flare is rarely a problem. With 300mm or longer...I'm pretty sure every picture I've had to discard due to flare or ghosting problems could be counted on one hand with fingers left over.

Bottom line: I can see ways this technology could be a good thing, but as it's often currently being applied, it strikes me as unlikely to produce any significant improvement.

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^{1. I can certainly think of a few specific lenses I'd love to see re-introduced with such coatings applied--great in other ways, but major problems with flare/ghosting.}