7

Anti-reflective coating is sensitive to fingertips and extra care is needed when cleaning camera lens. I've heard a couple of stories where a camera owner used some organic solvents and ended up completely removing the coating from the outer surface of the lens (the one which is the easiest to plant fingertips on).

What actually happens if you have the anti-reflective coating on the most outer surface of camera lens seriously damaged or fully removed? What effects on camera functioning will it have?

  • Fingerprints tend to be acidic; it's that rather than oils/organic solvents that attacks some old AR coatings. Rubbing too hard could also damage the old coatings – Chris H Oct 11 '16 at 9:09
10

Up until the late 1940s and into the 1950s, camera lenses didn't have coatings. The result was much higher incidence of lens flare and reduced contrast in the presence of bright light sources.

Touching a lens with your fingertips will not remove the coating! Lens coatings are much harder to remove than that, and would generally require some kind of abrasive rubbing to remove.

Zeiss has a detailed PDF on this topic, including comparison images taken with coated/uncoated lenses, if you are interested in finding out more:
About the reduction of reflections for camera lenses: How T*-coating made glass invisible

  • Cool stuff you linked to. Could you please include its title (About the reduction of reflections for camera lenses - How T*-coating made glass invisible) into your answer so that it can be googled after it's moved somewhere else? – sharptooth Oct 10 '16 at 11:09
  • This is misleading, as the contents of fingerprint oil can and will damage coatings if not removed relatively quickly. – Carl Witthoft Oct 10 '16 at 11:24
  • 1
    It should be noted that the vast majority of the effects seen in the comparison photos at the link are due to the surfaces of the internal lens elements not being coated and not the absence of coating on the outside of the front element. – Michael C Oct 10 '16 at 15:37
4

Anti-reflective coatings are used to reduce reflections on glass-air and glass-glass surfaces. These reflections, if not suppressed, can lead to light loss, secondary images (lens flares) or glare, which reduces overall image contrast. So losing a layer of coating might increased occurrence of these phenomena, especially in the presence of bright light sources shining into the lens.

However, most modern lenses use multiple layers of coating on multiple lenses, so the effect of simply removing the layer from (one side of) the front element will probably be small. I don't know of any direct comparisons, but there are examples of severely scratched or dirty front elements producing very little image degradation except under extreme circumstances (again, bright light source shining directly into the lens).

3

About lens coating:

Optician Harold Dennis Taylor observed that older lenses on the shelf passed more light than new ones of identical design. He investigated and discovered that the older lenses were “bloomed”. They had acquired a thin layer of schmutz thanks to the London smog caused by coal burning brought about by the industrial revolution. The “bloom” increased the light transmission by about 4%. Taylor patented a lens coating process in 1904.

By the end of World War II, most cameras sported coated lenses. The coating mitigates reflections off the polished glass surface. Today we coat in a vacuum chamber depositing layers of barium, cadmium, sodium, lithium and magnesium etc. It is the thickness of the coat that does the trick. The coat must be ¼ of the wavelength of the light ray to be controlled. A modern lens is multicoated, each coat to handle a different color. A modern lens with multiple elements, each coated, is greatly improved as to speed, plus the coating reduces flare and ghost images.

The coat on the front and rear surface is quite durable and likely not harmed by normal lens clearing. If the front lens coat is injured, likely you will never see any degradation.

  • 1
    Your first two paragraphs read as though they're a quote from somewhere. If they are, please give attribution. – FreeMan Oct 10 '16 at 18:37
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    These paragraphs are my writing. I did the research many years ago when I was teaching this stuff. Taylor's paten for applying suphuretted hydrogen to artificially age lenses # 29,561/04. – Alan Marcus Oct 10 '16 at 21:46
  • So that's why they sound like they're from a research paper! Excellent. If that's published anywhere, please feel free to edit your post and pat yourself on the back for it. In any case, nicely done. – FreeMan Oct 11 '16 at 12:36
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As others have said the outer coating will be a hard coating and quite robust - it would take some abrasion or strong chemicals to remove it. With modern coatings it may be harder than the lens glass itself and provide protection to the lens surface. Older coatings were much less robust and needed careful handling.

The effect of removing it would be that the outer surface reflects some light instead of transmitting (about 4% typically with normal glasses and visible wavelengths). This is probably insignificant in terms of exposure but if you were to add filters you would likely see the multiple reflections of bright sources from the lens front and back of the filter.

0

I really do not know. I'm writing a totally unfundamented answer... but...

I just want to emphasize, the "most outer surface". The light reflected by this layer wil not produce any flare, because will be bounced to the infinite space, not inside the lens, except in the case you have an aditional external filter.

So there is a chance this coatings are more protective, like some anti mostiure, anti fog or something like that.

There is also a chance that this coatings has something to do to reduce some kind of chromathic aberration, filtering some extreme incident beams.

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