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Me and my friend both own the Nikon 24-70mm F/2.8G lens. When we met today I put my camera on the table next to his. We noticed that the front element of our lenses must have different coatings because they reflect light in different colors and the observation wasnt a matter of the viewing angle. Is it possible that the coatings on the lens where changed over the years? Do they wear out? I own that lens much longer than him and I used it almost 100% of the time outside where he mostly shoot indoors in lower light. Or can this even be a sign of a counterfeit lens?

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I would like to know what they have changed and why.

My lens is the blue one. Mine was bought new and he bought his used. My lens has serial number 9005xx and the other one has 8873xx. This could actually explain something.

Michael C
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Arji
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  • Given the industrial investment required to produce a lens of decent quality, the only way to make a "counterfeit" lens is if Nikon contracts another company to make a lens for them (likely, entry level stuff), and this company puts some of these lenses directly on the market (possibly avoiding some quality control...). But that would be a very dangerous game to play for that company... – xenoid Jun 05 '21 at 19:43
  • Would be interesting to know the serial numbers. Might be a clue as to where in the production sequence each lens was produced. Probably shouldn't post the actual numbers (not sure why, but doesn't seem to be an entirely good idea), but posting the difference might work. – BobT Jun 05 '21 at 20:57
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    My lens is 9005xx and the other one 8873xx. This could actually explain something. I would like to know what they have changed and why. – Arji Jun 05 '21 at 22:10
  • Were both lenses bought new? Or was at least one of them bought used? – Michael C Jun 06 '21 at 02:16
  • Mine was new and his one is used. – Arji Jun 06 '21 at 06:51
  • @BobT I've never understood why people think it is somehow "risky" to publish the serial numbers of their things. If the item has been registered with the manufacturer, then one has verifiable proof that one was in possession of the serial number well before anyone else could attempt to document that serial number as theirs. And it's not like most serial numbers have a check digit in them like a banking account number or social security number. It's pretty easy to guess serial numbers if one has only a few examples from the same product. In the case of camera gear, there are often databases. – Michael C Jun 06 '21 at 22:18
  • Related: Why does Canon have Two Kinds of Nanotech Lens Coatings? – Michael C Jun 06 '21 at 22:20
  • @MichaelC You're correct. I've never completely understood it either. Usually it's explained as a way for someone else to falsely claim that the equipment is theirs or to register the equipment as theirs. I was trying to be 'sensitive'... – BobT Jun 07 '21 at 01:21
  • xenoid err... there has been quite a commotion about counterfeit canon primes in the last few years.... – rackandboneman Jun 08 '21 at 13:02

3 Answers3

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The coatings do not have a color and do not wear out with exposure to sunlight... it's also highly unlikely to be a manufacturing tolerance/variable issue IMO (although that is possible).

It's quite possible that Nikon changed the material the coating is made from, or the thickness of the deposition, over the years for some reason (e.g. from Magnesium Fluoride to Silicone Dioxide to fine tune the color response/transmission for newer sensor technologies). But I don't know how you would find that out for certain.

Steven Kersting
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    Anti-reflective coatings may not have a 'color', but they do reflect and absorb different wavelengths at different levels. Reflections from coatings can most definitely, and often do, have a color shift from the light they are reflecting. – Michael C Jun 07 '21 at 21:53
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    I'm aware that there is typically a color shift to the reflection because the AR coating isn't entirely effective (exhibit "residual color"). But there isn't much of anything that is going to cause them to change color... e.g. what interacts with Silicone Dioxide (quartz)? Sure, you may be able to scrape (or etch) them off, but that's not the same... – Steven Kersting Jun 08 '21 at 12:34
  • Read Roger Cicala's blog regarding the fragility of the fluorine coatings they're putting on top of the others. – Michael C Jun 08 '21 at 15:54
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    It's a PTFE type coating; and such coatings are surprisingly susceptible to scratching. Canon, Sony, and Tamron are using the teflon based coatings as well now (at least on some lenses)... maybe protective filters will become more useful again :>) – Steven Kersting Jun 08 '21 at 18:02
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I would like to know what they have changed and why.

I guess it is possible that Nikon modified the coating of the lens model between production runs, but I think it would be highly unlikely.

My lens is the blue one. Mine was bought new and he bought his used. My lens has serial number 9005xx and the other one has 8873xx. This could actually explain something.

Since your friend more recently bought his lens used, which actually was manufactured earlier than yours based on the serial numbers, I think it is far more possible that (one of) the previous owner(s) used something they might should not have used to clean the front of the lens. This either removed one or all layers of the coating or chemically reacted with it to alter what colors it reflects/and absorbs and what colors pass through it at the highest rates of transmission. Or maybe it was either you or your friend who used something to clean one of your respective lenses that probably shouldn't have been used?

Roger Cicala at lensrentals.com has noted that some of the more recent "improved" lens coatings from several manufacturers are more fragile and more care must be taken when cleaning them to not damage the coatings. In the past, most lens coatings on the front of lenses were fairly robust. The 'G' model of this lens came out in 2007 and was supplanted by the 'E' model in 2015, though apparently both are still in production. I'd expect the 'G' model to have fairly hard to damage coatings on the external surfaces. The 'E' model includes at least some elements coated with Nikon's 'Nano Crystal Coat'. The front and rear element have fluorine coatings, which are supposed to be smudge and smear resistant. But it is fluorine coatings that Roger Cicala has been less than thrilled about.

If that is the case it's not the end of the world in terms of color. Especially if one shoots raw and does careful color correction in post processing, the end result will not be significant at all. It just might take slightly different color correction settings to get the same result from one lens to the other. If one does detailed color calibration using a tool like X-Rite's Color Checker, the color profile generated using that lens will pretty much correct for any slight color shift. Of course, one would need to do a different color profile for each lens one uses on each camera, and then use the appropriate color profile generated using the particular camera-lens combination when converting the raw files, to get results that exact.

I'd be more concerned about the anti-reflective properties having been negatively affected. This might show up in reduced flare resistance and an overall loss of contrast when shooting into harsh backlight or with very bright light sources just out of frame. The reflection from the lens on the left in the photo not only seems to be bluer, but also brighter. This might indicate that the anti-reflective properties of the coating on the front of the lens has been reduced somehow.

It also might be possible that one of the two lenses in question has some evenly distributed smudges due to skin oil from fingerprints or other contaminants. I've found that if I try to use dry microfiber cloths to clean lenses, as many people seem to do, all it does is spread some contaminants evenly over the surface of the lens. To get the lens clean I must use a cloth moistened with a few drops of lens cleaner, and then dry the lens with a fresh, unused portion of the microfiber cloth. I've also found that microfiber (and other) cloths that have been contaminated with skin oil will spread it on a lens that doesn't even have a smudge to begin with! I specifically handle only one side of my "clean" microfiber cloths used to clean lenses and only allow the other side to contact the lens. Once they've been used a few times I replace them with a fresh cloth and use the older cloth for less critical tasks, such as for household cleaning.

Michael C
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    FWIW I once cleaned a telescope lens too aggressively and result was nothing like the difference between the two lenses OP posted. My experience is that you can not just remove one layer of coating, it all comes off. You see clearly coated vs uncoated (where it came off). – Joep van Steen Jun 07 '21 at 00:20
  • @JoepvanSteen Are you suggesting that all coatings on all lenses of any kind are identical? – Michael C Jun 07 '21 at 21:49
  • No? All I'm saying that coatings are so thin that they come off when cleaned to aggressively in my experience. – Joep van Steen Jun 08 '21 at 23:32
  • @JoepvanSteen And then the lens will reflect light differently, no? But there are also some layers that are more fragile than others. Especially the newer fluorine based coatings. – Michael C Jun 09 '21 at 00:02
  • Yes, lens will reflect differently then in parts were coating was 'lost'. But it did not go from even blueish to even purplish like in OP. Damaged portions reflected without color so to speak. So my guess is we're looking at two different coatings rather than an intact and damaged. In my case was a wo petzval telescope, no visible effects when imaging though. – Joep van Steen Jun 09 '21 at 10:20
  • Again, you're assuming your experience is universal. If the top layer is far more fragile that the layers underneath, it's quite conceivable that the top layer could be removed without removing the more robust layers below. – Michael C Jun 10 '21 at 01:38
  • I am not, but whatever. What you're seeing here is two lenses with different coatings. – Joep van Steen Jun 11 '21 at 11:36
  • @JoepvanSteen Which is what all of the three possibilities suggested in this answer say. The only question is how they got to be different: change by Nikon, coating(s) removed from one lens, or additional coating (of contaminants spread evenly) added to the other. – Michael C Jun 11 '21 at 21:32
  • @JoepvanSteen If you're so convinced you know exactly what the difference is, where is your answer? – Michael C Jun 11 '21 at 21:34
  • My money would be on changed by manufacturer, I'm with Steven Kersting. – Joep van Steen Jun 12 '21 at 00:57
  • I never claimed to know exact difference. – Joep van Steen Jun 12 '21 at 00:57
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The English optician Harold Taylor and Physicist John Strutt independently observed that aged lenses transmitted 4 to 6% more light than new ones.

Taylor went on to experiment and artificially aged lenses using various methods. This truly was an important discovery because new lenses suffer a 4 to 6% loss in light due to light being reflected from their polished (mirror like) surfaces. Now lenses used in cameras and telescopes are complex systems with many lens elements sandwiched together. Thus, multi-lens element systems can suffer a light loss of 40 – 50%.

Old lenses acquired a natural coat of schmutz deposed by smoke from coal burning steam engines and building heating.

Today, many coating methods are used. It is the thickness of the coat that does the trick. If the coat is ¼ wavelength thick, light traverses the coat and most of the reflected light from the polished glass hits the air coating junction and is re-reflected. Thus rays ordinary lost will contribute to image brightness.

This discovery and remedy is important as modern lenses often use many elements and groups. Losing 4 to 6% at each junction translates to quite a high loss. Most loss is from internal junctions (glass to air and glass to glass) within the barrel. Each internal reflection caused light rays to go astray, and many misdirected rays bathed the film/chip with light scatter called flare. Flare is devastating; it degrades the image by reducing contrast. Gross reflections cause glare spots.

Many coating methods are used. One method is to place the lens to be coated in a vacuum chamber. The air is evacuated and the mineral that will be the coat is heated causing it to vaporize. This vapor condenses on the glass lens and coats and etches. It is the thickness of the coat plus the material that does the trick. Each coat is optimized for just one color of light. A modern lens has multiple coats applied. Each coat is different in thickness. A high-quality lens can have as many as 7 thru 11 coats.

As time passes, coating technology advances. Likely each discovery will give small improvements.

The color seen when looking at the lens is based mainly on the thickness of the first coat. Coating materials and methods change as this science advances.

A tip of the hat to Harold Taylor.

Alan Marcus
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