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Dirty optical element - positive meniscus
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PostPosted: Tue Apr 22, 2014 6:59 pm    Post subject: Dirty optical element - positive meniscus Reply with quote
I just purchased Photax f8/500mm for 20€ mounted on Zenit camera with flash. The lens had one dirty element inside but I still think it was a good deal. So I decided to open the lens (it was pretty simple) and to clean the lens but there is a big problem. The dirt is semi-transparent white looking texture and it's invulnerable to almost any chemical I have found around.

Note: I don't know how to name this thing properly because I'm not native speaker as you can see.

Chemicals aren't effective so I decided to use tooth paste to burnish the lens but I can't see any noticable effect (maybe I don't have tooth paste with micro-granules). I thought about purchase of some glass burnishing paste. Maybe for car windshield repair?! I don't know.

It's the first element inside the tube from sensor's side and with wikipedia I could identify it as positive meniscus. Maybe there is an another solution - maybe I can order one element from the internet (with right diameter and FL)?! But how can I acquire enough details to order the right one?

What you can recommend? Did you meet with this before? Any help will be appreciated.

PS: this optical element didn't have any coating layer. It's just glass which I want to make super-shiny before use.


PostPosted: Tue Apr 22, 2014 7:18 pm    Post subject: Reply with quote
if toothpaste didn't get it off I don't know what will, haze is a horrible thing!! I say use the lens as is and if its too bad get something else.


PostPosted: Tue Apr 22, 2014 7:30 pm    Post subject: Re: Dirty optical element - positive meniscus Reply with quote
asfethan wrote:
The dirt is semi-transparent white looking texture and it's invulnerable to almost any chemical I have found around.


Maybe it is not dirt, but a badly polished lens. You know, those cheap lenses never have a good quality control. Try a car polishing paste as a last resort.


PostPosted: Tue Apr 22, 2014 7:38 pm    Post subject: Reply with quote
In the near future I plan to visit drug store to collect some HCl and H2O2. Maybe those two will be a game changers...

Gerald wrote:
Maybe it is not dirt, but a badly polished lens.


How can one achieve this? Btw an element placed before this one in distance about 3-4cm is perfectly clean. I don't understand what happened to this one...

PS: btw I will do everything to save this one because it's 500mm prime and I want to see it in action so much! Smile


PostPosted: Tue Apr 22, 2014 7:58 pm    Post subject: Reply with quote
Your lens looks like the unpolished lens on the left?



PostPosted: Tue Apr 22, 2014 8:09 pm    Post subject: Reply with quote
No, it looks like this:
http://2.bp.blogspot.com/-Hl5VMJ1Yik0/T6a61gMaZQI/AAAAAAAAVxw/HSyubZJKug4/s1600/06-05-2012_06.jpg but with
different barely noticable pattern...


PostPosted: Tue Apr 22, 2014 9:11 pm    Post subject: Reply with quote
My guess is - fungus. But I might be wrong. The marks might be etched in the glass, probably deeper than a rub with any abrasive can remove.


PostPosted: Tue Apr 22, 2014 9:16 pm    Post subject: Reply with quote
asfethan wrote:
No, it looks like this:
http://2.bp.blogspot.com/-Hl5VMJ1Yik0/T6a61gMaZQI/AAAAAAAAVxw/HSyubZJKug4/s1600/06-05-2012_06.jpg but with
different barely noticable pattern...


This definitely does not look dirt. He seems to be scratches on the glass surface. I suspect that someone tried to clean the lens with an abrasive material. I suggest you take the lens to a repair shop for glasses and contact an optical technician. He can probably make a better diagnosis.


PostPosted: Tue Apr 22, 2014 9:19 pm    Post subject: Reply with quote
I'll try. Thanks for advices. I'll keep inform you about my progress.


PostPosted: Tue Apr 22, 2014 9:20 pm    Post subject: Reply with quote
Did you try the lens?
I had some horrible looking glass that performed flawlessly in 90% of the situations (when not pointing them straight into a light source, basically): if your lens performs acceptably, I wouldn't risk making more harm with chemicals or polishing it.
If it performs badly, well, nothing to lose.


PostPosted: Tue Apr 22, 2014 9:25 pm    Post subject: Reply with quote
That haze is decreasing optical quality even in the viewfinder so I didn't try to shoot photos. It's very milky.

I wonder if the optical technician will be able to tell me some details about this element. Maybe I can replace it afterward...


PostPosted: Tue Apr 22, 2014 10:32 pm    Post subject: Reply with quote
I have a very similar situation with my Kaleinar 5N. The lens was unused in it`s original box and kept in a very good place, so I knew it was not fungus. When I took the lens apart and tried cleaning it, the milky stuff wiped of, but the surface of the lens was still uneven under strong light. The image was no longer bad in the VF but I did not test the lens on my NX20. It seems that the coating "went bad" and peeled of or something...


PostPosted: Tue Apr 22, 2014 11:03 pm    Post subject: Reply with quote
This is the rear element and it doesn't look like it ever had coating. So that's better for me. I still didn't give up and I think it's a bit better - microfiber cloth with tooth paste technique but I'm no longer moving with cloth on element surface but element on cloth.

Btw read this - especially part about fungus.

Quote:

There are basically two types of mold and fungus, oxygen loving and non-oxygen loving. Oxygen loving mold typically exudes carbon dioxide as it lives and is relatively harmless to lenses and coatings. But it does exhale water which can cause rust. It generally will not consume plastic, rubber or foam. Mold that thrives in an oxygen deprived environment exudes a very powerful acid. This acid is responsible for coating damage and lens etching. It also dissolves rubber, some plastics and foam. Determining which type of mold inhabits a particular lens or camera is almost impossible for anyone but an expert to do based upon appearance. Mold is like mushrooms and can have a variety of appearances based upon what stage of life it is in. It's usually best to just assume its the worst kind.


http://www.zeisscamera.com/services_lens.shtml

As this specialist mentioned in that artice it's hard to keep lens fungus/mold free if you don't have a special cabinet with controlled humidity and even this can fail.

So I think this is my case and I'm still trying to save this lens on my own. Rolling Eyes


PostPosted: Wed Apr 23, 2014 1:03 am    Post subject: Reply with quote
Recently posted a question here about haze on rear element http://forum.mflenses.com/hazed-lens-elements-do-they-get-worse-with-time-t65641.html ...
I subsequently got the part dismantled (there was another screw-join I'd missed) and the clouding was only on that one, inner, surface.
It lessened, though did not all disappear, with the application of Isopropanol, ROR lens cleaning fluid and a microfibre cloth.
It does seem to be a surface coating that deteriorates.
Having seen this and other glass elements with hazing, I'd say it looks like scratches on yours as well as haze.
With luck, perhaps these scratches are only in the defective coating?
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