Polarizing filter delamination?

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mnmyco
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Joined: Tue Aug 28, 2018 11:03 pm

Polarizing filter delamination?

#1 Post by mnmyco » Tue Oct 08, 2019 2:44 am

I recently purchased a AO polarizing condenser, but the filter looks a bit odd.

Image

Is this an issue?

MNMyco

PeteM
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Joined: Tue Dec 06, 2016 6:22 am
Location: N. California

Re: Polarizing filter delamination?

#2 Post by PeteM » Tue Oct 08, 2019 4:54 am

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.

mnmyco
Posts: 144
Joined: Tue Aug 28, 2018 11:03 pm

Re: Polarizing filter delamination?

#3 Post by mnmyco » Tue Oct 08, 2019 5:46 am

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?

MicroBob
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Location: Northern Germany

Re: Polarizing filter delamination?

#4 Post by MicroBob » Tue Oct 08, 2019 11:08 am

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

Hobbyst46
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Re: Polarizing filter delamination?

#5 Post by Hobbyst46 » 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 ?
Zeiss Standard GFL+Canon EOS-M10, Olympus VMZ stereo

MicroBob
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Location: Northern Germany

Re: Polarizing filter delamination?

#6 Post by MicroBob » Tue Oct 08, 2019 1:50 pm

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.

mnmyco
Posts: 144
Joined: Tue Aug 28, 2018 11:03 pm

Re: Polarizing filter delamination?

#7 Post by mnmyco » Tue Oct 08, 2019 5:34 pm

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

MicroBob
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Joined: Sun Dec 25, 2016 9:11 am
Location: Northern Germany

Re: Polarizing filter delamination?

#8 Post by MicroBob » Tue Oct 08, 2019 5:53 pm

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.

PeteM
Posts: 1302
Joined: Tue Dec 06, 2016 6:22 am
Location: N. California

Re: Polarizing filter delamination?

#9 Post by PeteM » Tue Oct 08, 2019 6:12 pm

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.

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