Does Lens Coating Fade Over Time?

[snegron]

I am curious to know if the coating used for lenses fades over time or not, especially on the interior elements? Lens coating seems to be one of the most closely guarded secrets of camera manufacturers, so other than the praise they all say about the benifits of multi coating, no one seems to mention how long it lasts.

I have several old Nikon lenses that appear to still have their coating intact (except of course for the exterior front element which has probably worn out in time due to wiping smudges and dust). However, I noticed that on a really old Nikon lens I had (a 50mm 1.4 for my S2 Rangefinder) the images did not look as color saturated and contrasty as they did with my Nikon 50mm 1.4 newer AIS lenses. lso, the colors were very bland despite the fact that I used the same film and shot the same subjects at the same time with different cameras.

It would be nice to know how long the coating lasts, especially if one is considering buying an old lens. Also, are there places that re-coat lenses? Would it be cost efficient, even worth it?

 

[glbeas]

The newer lenses use better coating and types of glass so the better saturation and contrast is not surprising. If the coating is not abraded theres no reason it won't last the life of the lens. Old uncoated glass will sometimes develop a coating from oxidizing of the surface and perform better than when new.
As for recoating a lens, it's cheaper to buy a new one than to have anything major done to the less expensive ones. Theres no way to pinch pennies with quality glass.

 

[snegron]

I wonder if UV light has any effect on the coating? One of the reasons I thought about the idea of getting a lens re-coated was because some lenses are no longer made, especially the ones for rangefinders. The lens I had was in near perfect condition except for the rather unsaturated images it produced. I no longer own that lens or the S2 rangefinder, so it's not a big issue now. However, I would like to get older Nikon lenses for my F's and would like to know if it's worth it to buy them cheap and spend the money getting them recoated? I know I can use newer lenses with my F's, but I like the look and build quality of the older lenses.

 

[David A. Goldfarb]

I don't think coating deteriorates over time as long as it's not attacked by fungus, but it can be worn down or scratched from cleaning or exposure to the elements, so it might make sense to recoat the front surface of an old lens. Focal Point Lens in Colorado offers this service, and it runs around $150-200 per lens surface (usually just one surface).

 

[Monophoto]

If the coating process were a dye, then I would be concerned about the possibility of fading.

But the process is actually a metallic deposition process - a microscopically thin coating of metal is applied to the glass by exposure to a vapor. Absent abrasion, its there for the duration.

Of course, if you insist on scrubbing you lenses - tissues, cloths, and perhaps with lens cleaning solutions - that can remove the coating. That's why the preferred way to clean lenses is to use a bulb blower to blast off any dust, and use a brush only if you must.

 

[keithwms]

David's answer strikes me as reasonable.

At least, as far as I know, modern coatings themselves won't deteriorate, but the glass itself might well. There is the famous "yellowing" in certain glass formulas and the tendency for less pronounced things to happen over time; I can imagine that some surface deterioration might cause the coating to lose uniformity. In the lab, UV really screws with any surface- our problem isn't so much an issue of the glass itself going south, as much as an issue of UV light pulverizing various particles onto the glass surface in such a way that it cannot be cleaned. But I guess the powers I'm thinking about are way beyond anything you get from daylight, so forget that! Routine abrasion would seem a much larger issue to me.

David, I was speculating on RFF whether a coating service might be able to apply a hot mirror coating to Leica M lenses (preferably one interior element) thus obviating the (in)famous purple blacks problem with the M8. So far nobody wants to cough up an M lens to let me see if it will work.

 

[snegron]

If the coating process were a dye, then I would be concerned about the possibility of fading.

But the process is actually a metallic deposition process - a microscopically thin coating of metal is applied to the glass by exposure to a vapor. Absent abrasion, its there for the duration.

Of course, if you insist on scrubbing you lenses - tissues, cloths, and perhaps with lens cleaning solutions - that can remove the coating. That's why the preferred way to clean lenses is to use a bulb blower to blast off any dust, and use a brush only if you must.

I guess that in theory it would be best then when buying a brand new lens or one that has been re-coated to immediately protect it with a brand new clear or UV filter before using it for the first time. For some reason, no matter how careful I am, I always manage to get a small smudge or finger print on the front element! I can get rid of the dust with a bulb brush, but the smudges can only be removed by wiping them with something.

An interesting note on lens coating; I was looking at some old post-war pictures in Brian Long's book, "Nikon, A Celebration", and they showed how coating was applied on Nikon lenses back in the old days. It looks like the glass elements were placed in a very large glass jar after being cut and ground. It looks like some type of gas process, not sure.

 

[Tom Hoskinson]

I guess that in theory it would be best then when buying a brand new lens or one that has been re-coated to immediately protect it with a brand new clear or UV filter before using it for the first time. For some reason, no matter how careful I am, I always manage to get a small smudge or finger print on the front element! I can get rid of the dust with a bulb brush, but the smudges can only be removed by wiping them with something.

An interesting note on lens coating; I was looking at some old post-war pictures in Brian Long's book, "Nikon, A Celebration", and they showed how coating was applied on Nikon lenses back in the old days. It looks like the glass elements were placed in a very large glass jar after being cut and ground. It looks like some type of gas process, not sure.

The large glass jar was probably a the Bell Jar - of a vacuum chamber - implying a vacuum deposition process. Back in the 1960s I used a Bell jar vacuum chamber system and metal sputtering to resurface the SLR mirror in my 4x5 RB Graflex.

 

[Dan Fromm]

Snegron, as has been pointed out earlier in the thread, coatings don't fade but they can be abraded.

What afflicted you, though, sounds like the consequences of (a) a slow shutter in your RF Nikon, causing overexposure, or (b) a thin film of lubricant on some of the suspect lens' inner surfaces or (c) your usual fears of making a bad mistake. Older lenses that get a bad rap because of (b) are often miraculously improved by a good cleaning. Shutters can be overhauled too. I'm not sure we can do to make you worry less, though.

Cheers,

Dan

 

[snegron]

Snegron, as has been pointed out earlier in the thread, coatings don't fade but they can be abraded.

What afflicted you, though, sounds like the consequences of (a) a slow shutter in your RF Nikon, causing overexposure, or (b) a thin film of lubricant on some of the suspect lens' inner surfaces or (c) your usual fears of making a bad mistake. Older lenses that get a bad rap because of (b) are often miraculously improved by a good cleaning. Shutters can be overhauled too. I'm not sure we can do to make you worry less, though.

Cheers,

Dan

Thank you Dan. I must point out however that;

a) the shutter speeds were accurate because the all the images were well exposed at different speeds and aperture settings. Indoor and outdoor shots looked just as pale and lacked contrast, kind of what they look like when I use my RB67 with the 90mm lens; virtually no color saturation at all.

b) the lens was perfectly clear and the images were all sharp. If it had some type of "thin film of lubricant" the images would have appeared to be soft. All the details in the images were tack sharp, even the strands of hair on subjects. I experimented with "soft focus" filters many years ago, both home made and actual filters, even shot many times on the beach where the salt water air causes a thin layer of smeary salt to form on the front element, so I can tell when there is a film coating. This lens had no lubricant smear or film whatsoever.

c) I never worry. I am worried now that you think I'm worried though...

 

[thuggins]

There is no "closely guarded secret" to lens coating. It is a common process; Monophoto's description gets at the crux of it. There is no problem with cleaning a coated lens. The coating is harder than the glass. That's why they apply coatings to eyeglass lenses, cell phone displays and numerous other transparent plastic items now, that would otherwise get scratched to heck in no time. Just be careful to blow off any sand or dirt before you wipe the lens.