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Jonnymorris
Tinkerer
Username: Jonnymorris
Post Number: 2
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 18, 2006 - 07:37 am: | 
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Hi! One of the lenses which came with the Praktica I bought has some fogging on the first internal element (looks like a big oily smudge on one side). This lens had one screw hanging out and one screw missing on the mount side, so I'm guessing someone tried to get into it before and failed. The lens is a "Multi Coating Pentacon electric 2.8/29" It appears to be a macro lens, though I'm not entirely sure. Any help / advice would be greatly appreciated! |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 1
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 18, 2006 - 03:05 pm: |
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I've taken apart a 29mm/f2.8 Pentacon with Exakta mount (intended for the RTL1000). I think it's really a Meyer Orestegon.
Assuming yours is basically the same, take out the serial-number trim with a friction tool. Due to the convex front element I used a ring of inner-tube rubber and the open end of a suitably sized jar. The front lens assembly (4 elements) unscrews with the outer slots. The front slotted-ring retains both the front 2 elements separated by a spacer, so be careful when you take them out that they don't fall out together and get damaged. |
Jonnymorris
Tinkerer
Username: Jonnymorris
Post Number: 4
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 19, 2006 - 04:59 am: |
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OK, I got the lens apart and have extracted the offending element, but the smudge on the glass just will not budge. I first tried lens cleaning tissue, rubbing quite hard, then some generic lens cleaning solution with a lens tissue, again rubbing hard, but it doesn't seem to have any effect. Any ideas? The smudge is on the inside side of the element. I don't want to use any harsh chemicals that will destroy coatings or whatever, but I will continue trying with an old t-shirt. |
Steve_s
Tinkerer
Username: Steve_s
Post Number: 4
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 19, 2006 - 02:37 pm: |
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You may have a growth of the dreaded fungus! Try cleaning it with ordinary vinegar, using a cotton-bud (Q-tip). DON'T rub hard with anything or you will scratch the lens!
If this works, check the other elements carefully for more fungus.
If you do a search, you should find quite a bit of info on this forum on cleaning lenses. |
Jonnymorris
Tinkerer
Username: Jonnymorris
Post Number: 6
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 20, 2006 - 03:59 pm: |
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Well, I took the lens element into my local Jessops camera shop and asked their advice, the guy gave it a rub with some special lens cleaner he had (I think he said it was Isopropanol), but it did nothing. Vinegar did nothing, and I'm not convinced it's any kind of fungus. It looks like a smudged thumb print, I suspect it may be some chemical that has been smudged on the glass with a stray thumb, possibly even at manufacture. Any further ideas from anyone are welcome, although it's looking like this lens is going into the spares tray. |
Glenn
Tinkerer
Username: Glenn
Post Number: 57
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 20, 2006 - 08:04 pm: |
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The most likely cause is that the lens has been opened up and a sweaty finger print has etched the coating. Still, I would first try using Acetone on the mark, just in case it is caused by varnish/lacquer.
If the mark is still there and you have definitely proved that it causes image degradation, you could always get out the tooth paste/jewellers rouge. Polish off the mark and all the coating on that particular element surface. You could end up with a usable lens instead of overloading the spares tray. |
Jonnymorris
Tinkerer
Username: Jonnymorris
Post Number: 10
Registered: 09-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 23, 2006 - 07:11 am: |
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Do you mean tooth paste AND jewellers rouge, or just one or the other? Where would I get jewellers rouge from in the UK?
I tried Acetone, negligible effect. It may have taken a bit of the shiney surface off the smudge mark (as well as some of the edge paint!) but it's still clearly visible when looking through the lens. |
Glenn
Tinkerer
Username: Glenn
Post Number: 58
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 23, 2006 - 08:38 pm: |
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No just one or the other. I have had my supply of jewellers rouge for years, came from a lab supply firm - now defunct. Try asking your local independent jeweller for name of his supplier of repair items. |
Eugen_mezei
Tinkerer
Username: Eugen_mezei
Post Number: 10
Registered: 08-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 24, 2006 - 12:53 pm: |
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You will damage more than repair with any abrasive paste (even with tooth paste). Reassemble the lens and use it with the fingerprint on the lens. You will not note it on the images. Use a parasolair, so you dont have reflexions on the thumbmark.
Eugen |
Johnlees45
Tinkerer
Username: Johnlees45
Post Number: 17
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 24, 2006 - 01:17 pm: |
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I bought some jeweller's rouge from a high-class glass and mirror retailer. They use it for getting rid of very, very minor scratches. |
Glenn
Tinkerer
Username: Glenn
Post Number: 60
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 24, 2006 - 08:43 pm: |
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Whilst I have not had the need to use the technique on 'hard' coated lenses, I have repolished a number of soft coated lenses with damaged coatings. In general these lenses have performed no worse than their uncoated brethren, when reassembled properly.
You will also note, I stated this technique should only be used when the 'mark' gives clearly visible image degradation. If the lens is not worth a professional repolish/recoat and is heading for the scrap box - what have you to loose? |
