MicrobeHunter.com Microscopy Forum

I just recently found a second Nedoptifa microscope and it has a polarizing setup. The lower filter is delaminated and I'd like to restore it. Are these kitted layers of glass or am I looking at something different? Could they be separated and 'rekitted'? I didn't get to the upper filter yet because it's in the tube. It flips in and out of the light path with a lever on the tube. Very convenient.

I know I could use replacements but I'd like to have the scope original and working

Regards,

Peter

Is this a cemented filter or one with an air gap?

I think it was cemented

Just checking to see if the stuff in the middle might possibly be some trapped liquid of some kind, that accidentally got in the air gap. It looks odd for a delamination.
I would test some solvents to see if anything softens what looks like cement along the edge. If you find one, that does, you might try to soften it and separate the two plates, clean them carefully and reassemble them with a new lens cement (available in tubes on ebay).
Try high strength ethyl alcohol, as a start but it is likely a synthetic solvent. Other easily available options are toluene, acetone or acetonitrile .
The cement would have originally been strain free. It will be hard to duplicate that upon re-cementing but you have nothing to lose but your time, since the filter seems trashed anyway. In re-cementing, letting the cement settle on a perfectly level lower surface, for 30 seconds or so, then carefully lowering the top element and settling it with light pressure is the method I use for doublets and with care, should reduce stresses in the cement.
The polarizing grid may present problems. I've not done this , just doublet lenses, so you would be paving the way on it. Good luck
I'd be interested in the results, if you end up attempting a repair. I have a similarly affected filter but not as bad, as the one you show.

If you find you need to replace the polarizer, there is a seller on ebay, who sells polarizing discs fro 8mm to 45mm diameter. http://www.ebay.com/sch/m.html?_odkw=&_ ... g&_sacat=0

Thank you for both suggestions. I might need both in the end. I'll try to soften the cement. I have quite a few solvents around but I don't want to damage the paint in the engravements. The filters are an interesting proposition to get thing working.

Still another question: So there are filters like these with an air gap? It seems unlikely to me some fluid would have got in there... The scope was used in a professional environment and was stored in an attic for a few decades after that.

I couldn't find the lens cement on ebay but I won't need it until parts are seperated. That's not a problem for now.

I'l let you know when I get results (either good or bad).

Regards,

Peter

I recently had the same issue with some polarizing filters on two microscopes I'm restoring (a Reichert Univar and a Wild-Heerbrugg M40). It is indeed delamination of the polarizing film between the two pieces of glass. Why they delaminate like this, I don't know; but you can get the things completely apart by soaking in acetone or Goof-Off for a couple of days.

In all cases, I decided to replace the existing filter with a new one. E.g., the one in the photo was replaced by a 25mm dia, 2mm thick, unmounted laminated glass filter from Edmund Optics (part no.43786), and fit in the old cell (a threaded ring that screwed into the bottom of the condenser filter turret before a 100x IC prism) just fine after enlarging the cell just a tad with a Dremel-like tool and its 240-grit sanding drum. It was glued into the cell with some Elmer's Probond Advanced (this glue was an experiment, but it's water-based, seems strong enough, and excess glue cleaned up rather easily). The Edmund filters are expensive, and aren't AR-coated, but are made in Japan. They have a very thin plastic polarizer sheet between two glass layers. Hopefully optical cements have improved in 45 years!

Since I saved the old glass pieces, I may try recreating one of the filters if I can find some very thin decent polarizing film (the stuff there before was about 1-2 thousandths of an inch thick).

Thank you for your very interesting and informative post. Yes that looks exactly like my filter and I already found that it still works although I can't compare to anything decent and/or modern.

One more question. I have acetone and could soak the complete contraption in that. But I'm hesitating to do that because I think the film in between the glass layers would be sacrificed. Or would you expect the film to survive an acetone bath?

The film may well be ruined by the soak; mine was (the filter for the Wild M40). It came out looking very corrugated and was very weak, so I threw it out. But you may want to replace your film, anyway. Or not, if the polarization is still taking place, and it's just a cosmetic issue, being the polarizer and not the analyzer. You could fit a clean linear polarizer filter for a camera in there, as a substitute, to see if a good filter makes any difference as to evenness of illumination, etc.

For what it's worth, I've successfully separated separated partly delaminated optics by soaking them in sizzling water for an hour or so, without any damage to coatings. The optical cement was Canada balsam.

Not sure about what it would do to the filter but it may be worth a try...

OK, that's a good idea. The heat could soften the balsam. My filter was made in the 50's possibly early 60's so with my little knowledge I'd say balsam is the expected cement.