8

I have been gifted an old Sigma lens from around the early 90s, but as is common with the soft-touch rubberised coating on lenses of this age, the material has started to degrade and has become sticky.

As a number of plastic formulae can be carcinogenic when they break down, I'm reluctant to use the lens until I can do something about it.

I have read a lot of information on how to remove the coating, and it seems that isopropyl alcohol will do the trick, so long as it's sufficiently pure.

I have enough 99% IPA to do the job, but this would mean removing all the lining and lettering on the barrel, which I would rather avoid.

As an alternative, I'm considering sealing the material with a transparent layer of varnish, and it has been suggested in a number of threads on various sites that polyurethane might do the job.

Although this has been suggested in many places, nobody has reported back with any detail about their success.

I'd be keen to know if anybody on here has been able to seal the rubberized coatings on a lens with polyurethane or another similar clear coating.

The lens elements themselves are intact and pristine, so I'd like to save the lens if at all possible. I'd expect that a water-based clear coat would be the best solution as anything with a harsh solvent would probably just dissolve the coating further.

2

As an update, I have resolved the issue with the attitude that I have some excellent optics sitting around unused, and that is simply not good enough.

The plan of using a clear varnish was abandoned as I don't know what effect the solvents in the acrylic clear coat will have on the remaining rubberised coating, and cannot find any information on the specific plastic recipe to confirm this.

As the end goal was to be able to use this lens, I've taken the messy and utilitarian approach of covering it in clear tape.

The degrading coating can't get on my hands or anything else in the camera bag, and the lens works beautifully on my f60.

As I have no intention of selling it and am not bothered by the ragged appearance of it, it's a perfectly usable solution which retains the printing on the barrel and around the aperture ring.

It looks dog rough, but works.

1

The previous owners of lenses, which have rubberized coatings that are degrading into sticky messes, were probably regular users of hand lotions and sun block. Many lotions are petroleum products that act as solvents that gradually dissolve rubberized coatings over years. To avoid the problem, wash hands with soap before using rubberized camera equipment.

Avoid using acetone to clean camera equipment because it would destroy other plastic components and lens coatings, which could make the lens useless. Alcohol seems fairly safe, but doesn't work very well. Since the sticky mess is a non-polar, carbon-based residue, a concentrated degreaser, such as "LA's Totally Awesome", can be used to remove the residue. Follow by wiping down with 70% alcohol, then again with distilled water, to remove any left over chemicals.

If there is any lettering you wish to preserve, you can lightly wipe the area with alcohol to clean it. Then coat with clear nail polish before degreasing. Remove and clean rubber grips separately from the rest of the lens.

When I've used degreaser, it seemed to only affect residues that could be rubbed away or scratched off. Metals, harder plastics, rubber grips, and lens elements did not appear to be harmed in the short term. However, it is prudent to avoid exposing lens coatings to degreaser.

0

Work in progress, will extend answer... some things might be specific to the 75-300 AF APO I am restoring right now...

At least some Sigma lenses from that era are actually of all metal body construction and have a tidy looking, anodized finish under the sticky soft coating. That coating can be stripped off completely with acetone and paper towels. Avoid getting any acetone on plastic parts or paint you do not want destroyed (eg the focusing scale window) - acetone is even more aggressive than nitro paint thinner. Obviously, you want none on the lens coatings either. The markings will obviously be gone.

If you never handled acetone: Noxious stuff. Flammable. Do not attempt to apply with a synthetic sponge or brush. If you must get any on your hands working with it, grease your hands afterwards.

What remains to be solved is how to deal with or replace the rubber "jackets", since they tend to develop some stickyness too...

  • I'd avoid acetone b/c risk damaging lens coatings. I've used concentrated degreaser (LA's Totally Awesome). I removed and cleaned the grips separately with degreaser on cotton swabs. The degreaser seemed to affect only residues that could be rubbed around or scratched off. I followed by wiping everything down with 70% alcohol, then again with distilled water. – xiota Feb 4 at 3:28
  • Does the degreaser actually remove the paint/rubber (which will become sticky again no matter how you clean it) down to the metal? – rackandboneman Feb 4 at 9:29
  • On a Sigma zoom lens, degreaser removed the residue down to the underlying metal, but took multiple passes. It wasn't as easy as I'd expect acetone to be, but the lens coatings were relatively safer. For some non-photographic items, it removed residue that had degraded to stickiness, but rubberized surfaces that hadn't yet degraded were left behind. With more effort, scrubbing, they could be removed, but I decided to leave it alone. The underlying material is a hard plastic, so acetone would have damaged it, while degreaser did not. – xiota Feb 4 at 12:01
  • This is actually a 70 - 210 AF APO, and does have the metal body with the zen soft touch coating. What I was trying to find out is whether the marking on the lens (specifically, the scale printed on the lens barrel itself) is printed on the metal, or on the coating. If the scale is printed directly on the barrel, I'll start tackling it with some IPA and elbow grease to clean it up once the weather improves enough to work on it outside. – Alex Feb 4 at 13:53
  • On the lens I had (different model from yours), the coating was over the lettering, but the lettering wasn't durable, so partially rubbed away along with the coating. – xiota Feb 4 at 15:33
-3

That is a great lens! I have dealt with this before. Alcohol is a quick fix, but it is likely to dry it out that will lead to cracks. I've used cornstarch, but that is just a band-aid. Do yourself a favor and get a good camera guy/person. That lens needs an overhaul. It will probably cost about $50 U.S. Once they get gummy like that there is no quick fix. Good luck.

  • I'm not expecting a quick fix in this case, just something that will make it workable. The overall appearance of the lens doesn't bother me too much, but I'd like to coat it with something that will provide a more durable finish, so long as it doesn't damage the coating further. – Alex Apr 3 '18 at 14:21
  • 1
    "That is a great lens!" How do you know this? The question only mentions "an old Sigma lens from around the early 90s" which could be anything. – Gerhardh Apr 4 '18 at 8:08
  • 1
    @David Carr - To be clear here, the optics are fine. If I was to take the lens for an overhaul, what would be done? Would the coating be removed and replaced? To do that would require the lens being stripped down, the coating removed, a new one applied, reprinting of the markings and reassembly. That's about 16 hours, at about £15 per hour for skilled work as a rough estimate. I did specify that I want to coat the lens to stop the coating degrading further, not spend fart more than it's worth getting it reconditioned. The rubber mix is wrong, it's breaking down. This is just damage control. – Alex Apr 4 '18 at 9:42
  • It doesn't have to be that dramatic. When I say "overhaul" I wasn't talking about the entire lens. I have a camera guy that would just replace the degrading rubber parts. Don't mess with the optics. That rubber does need to be replaced or you will have a mess on your hands. I could probably have that lens refurbished for around $30-$45. – David Carr Apr 4 '18 at 15:55
  • The entire coating is degrading across the whole lens. The quotes i’ve had for repair are greater than the cost of replacing the lens. I’m going to seal it with an acrylic solution and see how it goes, and if it’s no good, i’ll just stick some clear tape over it. – Alex Apr 4 '18 at 16:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.