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Polarizing filter delamination?

Posted: Tue Oct 08, 2019 2:44 am
by mnmyco
I recently purchased a AO polarizing condenser, but the filter looks a bit odd.

Image

Is this an issue?

MNMyco

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 4:54 am
by PeteM
Certainly looks delaminated.

Try it - you may be satisfied with the image.

Seems you have three options: 1) Use it as is; 2) Return it; 3) Replace the polarizing element.

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 5:46 am
by mnmyco
Just got it apart. It is in between two glass disks and that is where it has become separated from both. I think this means it should work. Has anyone worked on an issue like this and have advice?

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 11:08 am
by MicroBob
Hi,
as far as I know the polarisator is usually from plastics. So I withstands heat and chemicals only so much.
If it were all glass you could do this:
- gently warming, the cement sometimes bonds again at 60-90°C
- dunking in xylene, adding canada balsam to the xylene, let soak, dry.

With the pol filter it might be less dangerous to just let immersion oil soak into the gap.

Bob

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 11:31 am
by Hobbyst46
There are fairly inexpensive glass polarizers on eBay. For example SVBONY. Diameter 25mm and probably other sizes too. They are sold installed in metal sleeves but the sleeve can be easily dismantled to extract the glass disc.
Would'nt it be possible to replace the delaminated piece in the condenser with a new polarizer ?

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 1:50 pm
by MicroBob
The typical photography polarizer has not quite the quality of a good microscopy polarizer. You get a less perfect extinction in x pol and sometimes a clour cast.

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 5:34 pm
by mnmyco
Hobbyst46 wrote:
Tue Oct 08, 2019 11:31 am
There are fairly inexpensive glass polarizers on eBay. For example SVBONY. Diameter 25mm and probably other sizes too. They are sold installed in metal sleeves but the sleeve can be easily dismantled to extract the glass disc.
Would'nt it be possible to replace the delaminated piece in the condenser with a new polarizer ?
Lots of the camera polarizing filters are circular polarizer and you want linear in most microscope applications.

I think I will dry some gentle heating. I am afraid things like xylene will destroy the plastic filter.

MNMyco

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 5:53 pm
by MicroBob
A circular polarizer is a linear polarizer with a retarder on one side. If you use it from the right side it works like a linear polarizer.

Re: Polarizing filter delamination?

Posted: Tue Oct 08, 2019 6:12 pm
by PeteM
My experience with delaminated polarizers (including some A.O.) is that they will often work well enough, as is, for casual observation and photography -- cool colors etc. Just keep them as far away as possible from a focal plane. I'll be interested if you have luck cleanly separating the three layers and then relaminating. I've been skeptical enough to not try.

I don't know enough about polarizers for chemical/geological identification to know if delamination would affect the paths enough to matter. But given those are typically $$$ scopes, seems spending $ to replace the polarizer would make sense. FWIW, I have one DIC-capable Leica scope with a slightly delaminated analyser and polariser -- and the images are still OK.

It's pretty easy in most cases to find a polarizer of the appropriate diameter to do a replacement if the delamination is severe. There is a huge range of camera polarizers from tiny ones meant to attach to cell phones on up. They can usually easily be removed from their mounts with the appropriate spanner, or have the mount turned down to fit. As MicroBob says, the cheap ones won't go to as dark an extinction and you may have to try reversing a circular polarizer to get the linear side in play. Edmund scientific and various used optical sources will also be a source for polarizers with higher extinctions.