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Steve_s
Tinkerer
Username: Steve_s
Post Number: 31
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 20, 2007 - 02:00 pm: | 
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Apologies for posting a non-camera question, but as it involves a lens fault, maybe it is slightly relevant!
Recently I bought a nice old pair of Wray binoculars. The lenses are coated, so they're post-war, but not later than the early '50s I would guess. The right-hand eyepiece was so cloudy you really could not see through it. Assembled, it looked exactly like a heavy coating of internal condensation. After dismantling it turns out that one surface of the second element (of 3) has the appearance of ground glass. It is quite uniform, apart from a small clearish patch near the edge, and it is clear at the edge where it has been masked by the mountings.
I have tried lighter fluid, vinegar, and ammonia, but nothing touches it and I have to assume it is a fault with the coating. I'm sure it isn't fungus, and none of the other elements have a trace of it. Has anyone else met this sort of defect on a lens, and is there anything I can try, other than attempting to polish the coating off? |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 239
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, April 20, 2007 - 05:41 pm: |
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i've seen something like this a few times: the front element of an Agfa Super Silette, the front element of a Jupiter-9, and the rear element of an old Rapid Rectilinear. The first 2 were coated, but obviously the RR was not; the Jupiter had the appearance of a random pattern of strings of bubbles across the surface, the other 2 looked more like a pattern of fine surface cracks. I don't have any idea what the cause (or causes) would have been.
I also had a 200mm Kowa tele lens that had an internal layer of coating that had become milky. In this particular case I tried to polish it off and discovered that the coating was extremely hard: I managed to polish out most of the haze without removing any detectable amount of the coating. In other lenses I've seen internal coatings so soft that the slightest touch would ruin them and they could be easily polished off of the glass.... so there's a tremendous degree of variability in this respect from one lens to another. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 32
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 21, 2007 - 07:57 am: |
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Thanks Rick. It looks as though I'll have to give polishing a try - at least there is nothing to lose. I have some "Fine Rouge Powder" I haven't tried out yet, though I'm not sure whether it is fine enough. It came from a clockmakers' supplies company, so it is presumably intended for cosmetic polishing rather than optical. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 240
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 21, 2007 - 11:10 am: |
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I don't know if there is any really good advice for polishing a lens ... any measurable removal of material can only harm the optics. Having said that, I have used Simichrome to remove haze and soft coatings with good success.
Hopefully the problem is confined to the coating, and the coating is soft enough to be removed. If so, you can use the coating itself as a guide: the coating is visible because of its thickness, which is 1/4 wavelength of light per layer - something as early as your binoculars will only have one layer of about 130nm (.00013mm) thickness - if you stop as soon as the purplish color disappears, you will not have changed the contour much. |
Wernerjb
Tinkerer
Username: Wernerjb
Post Number: 120
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 21, 2007 - 12:28 pm: |
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Hi Steve, just because it comes as a supply for watchmakers the powder you have is right as it is for grinding extra hard glass surfaces of premium divers' watches! I have used the same stuff ("white/grey/red emery powder") for repolishing scratched surfaces of otherwise lost lenses. But please note, this may be the last straw, and it may ruin a lens forever if you grind it down too much, W. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 33
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 21, 2007 - 02:07 pm: |
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Thanks for the information. Hopefully I'll be able to try the rouge powder on a scrap lens element tomorrow. What would be the best thing for applying the polish? (It is mixed with water to make a paste, according to the instructions). The job will obviously need more pressure, applied over a longer period, than normal cleaning/de-fungusing operations, with a much greater risk of scratching. |
Wernerjb
Tinkerer
Username: Wernerjb
Post Number: 121
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 22, 2007 - 03:32 am: |
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Steve, I used a soft cotton cloth to which I applied the paste in very small quantities, I had to add more water during the procedure. Be careful, your fingernails and everything that gets into contact with that red stuff with take on that nasty colour! I also tried wet cotton swabs which I then only dipped into the powder, ("red") has the finest grain in my case. My test objects were hazy ond/or scratched lenses (old Agfas, Petris, Olympus 35 RCs, Yashicas, etc).
The coating of front lenses, although harder than the one on internal lenses, will be gone after only slight rubbing. One of the Oly lenses was so heavily scratched that picture taking was no longer possible. For experimental purposes I separated the front lens from the camera and mounted it to a makeshift polishing seat and focefully grinded it down so that only one major scatch was left, BUT then the lens was no longer sharp and it was not possible to correct that by readjusting the infinity point, in other words, repolishing lenses certainly has its limitations. For taking off traces of fungus I have tried cigarette ash, but this also is a borderline case, (cf. the following thread: https://kyp.hauslendale.com/classics/forum/messages/3/2166.html , W. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 34
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 22, 2007 - 06:33 am: |
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Thanks for the tips, Werner. I have had a couple of tries on my scrap element, but I think it is a bad choice as a test piece because I suspect it is very hard coated (and probably multi-coated). It came from a fairly late Japanese lens.
I used one of those soft cleaning cloths they give you when you buy a pair of spectacles. For the first attempt I tried quite heavy pressure. The colour of the coating polished off but the surface remaining was not smooth. I tried on a different area with much lighter pressure, but got the same result. Further polishing improved this (so possibly the uneven surface was a second coating) but there are lots of tiny "lumps" of coating remaining which seem too hard to polish off.
I think I will have a go at the binocular lens next (hoping the coating is soft), but I will take it very slowly and spread the job out so that I don't get bored and careless. I will report back here any result for the record, but don't hold your breath, it may take a while! |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 243
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 22, 2007 - 08:56 am: |
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getting it off evenly is more important than getting it off quickly: the coating layer is your only guide to the amount of material you've removed, so as you see the color start to change in one area move to another so that you keep it equal all over. once you can't see the coating any more, stop as soon as possible to avoid changing the contour of the surface. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 35
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 29, 2007 - 05:35 am: |
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Well, the coating disappeared in the first 5 minutes, but unfortunately the fault was on the glass, like Rick's Rapid Rectilinear, though the fault appears as a mass of tiny pits. I carried on polishing, and have done a total of maybe 4 hours, and the lens is almost completely clear, but of course it is optically rubbish! I had a vague idea that maybe in a pair of binoculars the human brain might be capable of resolving the errors(!), but I've stripped the other eyepiece, and I find that the same element is showing the same problem, to a lesser degree, so there is really no point in going any further. The cause is obviously something to do with the type of glass used for this particular element.
On the plus side, I'm very impressed with the effect of the rouge powder, which certainly seems to be fine enough. I have a couple of lenses with badly scratched coatings which would almost certainly be better off with the coating removed, and the rouge should do this very well. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 259
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, April 29, 2007 - 07:35 am: |
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Don't necessarily assume that a lens with scratched coating would be better off without the coating. The scratches tend to negate the coating's beneficial effect, but it would take quite a bit of it to make it worse than not having the coating at all. Of course, it will look better for display, but it may not deliver a better image. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 36
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, May 20, 2007 - 06:42 am: |
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I reassembled everything, just to get the parts out of the way, and found that the result didn't look that bad. I hate to throw anything away, so I did a bit more polishing on the faulty element, and did the same on the cloudy element in the other half. The rest of the optics cleaned up quite nicely, and I now have a fairly usable pair of binoculars! There is still a little cloudiness, but I've seen worse, and there is no distortion or loss of definition that I can detect.
Certainly the amount of glass I have had to polish away would make a camera lens scrap, but for binoculars there does seem to be more leeway. |
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