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Steve Hall
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Votes: 0 (Vote!) | | Posted on Friday, February 11, 2005 - 02:33 pm: | 
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I am trying to restore a Nikkor 500mm F8 mirror lens that suffered some water damage (before I got it). The mount area got pretty wet and the rear filter was completely covered with a red rusty coating. I have cleaned the front element and the mirror and gotten everything else in good shape except the rear element which has a rusty streak across an edge. I have tried the usual Ronsonol, denatured alcohol, Windex, water, white vinegar and very briefly some kitchen cleaner (no abrasives) with barely noticeable results. I was tempted to try CLR but was afraid it might do more harm than good. Has anyone tackled this kind of problem before? Is there any hope? I would really like to get this very nice lens going again. Thanks in advance for your help. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 05:01 am: |
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Hi,
Is the rear element out of it's metal mount?On old uncoated glass I have used a solution of either OXALIC acid or PHOSPHORIC acid with great results.Oxalic acid is crystalline and poisonous,so take care if you get some.Try a 25% solution max.
Otherwise here in UK,our local supermarket sells a liquid stain remover,this item is found in the laundry dept.The label says 'Removes rust and grass stains'etc,I guess it must be biological from other label details,but I have used it to remove rust staining from satin chromed steel very sucessfully.Sorry Icannot be more helpfull,but if lens is unusableas is what have you got to loose?
On the topic of useful household cleaners for restoration use,here in UK there is new liquid spray called CILLIT BANG {were do they find these names} which removes lime scale etc.The TV add shows copper coins being soaked and coming out bright.I have just used it to slightly cleanup the brasswork on an unknown wholeplate camera.Used a cloth dampened with the stuff.Results amazing brasswork clean,but not overly so and camera now has an old well- cared -for look.Also did same on old brass bound bible my wife got via ebay,again results gave a good patina.I shall keep a supply on my bench.
The funny thing is that some years ago I built a test rig that reproduced rust staining on glass and painted surfaces-research into cleaning rail stock in days of castiron brake blocks.Could reproduce your problem now on coated lens and give you the definitive answer,but would take approx 6 weeks!You just dump 1ib iron filings in water and let water drip onto the lens,presto rust stained lens! |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, February 14, 2005 - 08:15 am: |
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Further to my last message.Just done small test whilst I was out with dog.Using Canon SSC optics,placed drop of 15% oxalic,10% phosphoric and proprietary kettle descaler on coated surface.Left to stand whilst out.Just examined under microscope-did not see any damage.Do not try automotive rust removers,they contain not only phosphoric but sulphuric and hydrchloric acids also;a no no on optical coatings.
Please note however that the previously mentioned research showed that the rust stain was attached at molecular level to substrate.Proved by electron microscopy,so even if red stain removed the surface may still show faint marks.
Still I have a 180mm/2.8 Sonnar that internally looks full of fog.Iuse it at 2.8 with pushed Tri-X and the film grain is the limiting factor,not the optics.Have had superb 20x16 but would never use for colour slides!So you may end up with a very useable lens,just know the limitations of the equipment. |
Steve Hall
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, February 15, 2005 - 07:20 pm: |
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Thanks Glenn for the information. The lens in question was soaking in flood waters with the mount end in the water, apparently at an angle from the position of the stain. The rust came from the steel retaining ring on the rear filter. I removed the filter and got it cleaned up OK with just soap and water but the rear element stain has been very stubborn. The rear element is still in the mount which complicates things; I don't want to start eating away at the aluminun mount. I had considered trying a descaler marketed here as CLR (calcium, lime, rust) but was afraid it might be too aggressive. I will try to find a stain remover for laundry and see what that does. If that fails I will probably try the Oxalic/Phosphoric acid. You're right, the lens doesn't have to be perfect to be usable. But I would like to get it as right as possible. Thanks again for you help. |
Glenn Middleton
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, February 16, 2005 - 07:51 am: |
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Steve,If still in mount do not use phosphoric except at low conc. ie 3-5%-just wet old lens cloth or tissue and keep wiping.Using fresh area or tissue for each wipe.Oxalic method the same,again start with low conc 3-5%.As I said my main experience is with old uncoated glass lenses and research I did in removing castiron brake-block dust stains from rail stock and cars carried by rail.Years ago here in UK we had a night motorrail service-drove your car onto wagon,you slept in sleeping car and you travelled from London to North of Scotland overnight.Started your holiday bright and fresh!Cars got covered in cast iron dust that bonded to paintwork-Only removed by acid,Oxalic in the end.That is nothing to do with cameras,but give it to you as evidence that I am fully aware of all aspects of this problem,but as stated have only quickly tested on Canon SSC coatings,
The stain remover in laundry section is yellow crystals with what looked like grains of detergent in it.It could be an organic acid.Will Regards Glennbuy another little bottle tomorrow and have a look.Might even be able to post you some,if substance is permitted in post.It is not expensive.Keep me informed |
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