Nikon analyser

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photomicro
Posts: 207
Joined: Thu Aug 03, 2017 10:28 am
Location: UK

Nikon analyser

#1 Post by photomicro » Sun Feb 11, 2018 10:49 am

My query concerns an analyser I acquired recently, made for a modern Nikon microscope, and as such, does not fit my Nikon stand, despite having a very similar dovetail. It is just a few mm out, which means the bottom bit is too big to fit the stand, and therefore the top too small for the binocular head. With such a small difference you wonder why they changed…oh well.

Anyway, during my cursing period at such bad luck, I marvelled at how thin the polarising material seemed to be, and investigated the degree of extinction with an existing piece of polarising material. I found the extinction to be excellent, but only one way ! By this I mean that if the polariser is put in front of it one way and turned, you get full extinction, but from the other side, you get nothing.

I have to admit to neither understanding how this can be so, nor why it should need to be a feature of the device.

Can anyone shed any light on this?

The device is a Nikon Y-ISA model 'A' analyser, and is said to fit (!) Eclipse 200 and 400 stands I think. (Mine are Optiphot and Labophot 2)

Mike

MichaelG.
Posts: 3980
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: Nikon analyser

#2 Post by MichaelG. » Sun Feb 11, 2018 11:24 am

Mike,

As I understand it [i.e. not very much] many Polarisers exhibit this unexpected characteristic: They act as circular polarisers in one direction and linear polarisers in the other. To get extinction with crossed polars they obviously need to be linear.

I did see a good note on the subject ... if I can find it, I will post it later.

MichaelG.
.
Edit: http://www.ray-optics.com/Polarization_Tutorial.pdf
.
Edit: some of these video demonstations are relevant too:
https://ocw.mit.edu/resources/res-6-006 ... al-optics/
Too many 'projects'

photomicro
Posts: 207
Joined: Thu Aug 03, 2017 10:28 am
Location: UK

Re: Nikon analyser

#3 Post by photomicro » Sun Feb 11, 2018 7:17 pm

MichaelG. wrote:Mike,

As I understand it [i.e. not very much] many Polarisers exhibit this unexpected characteristic: They act as circular polarisers in one direction and linear polarisers in the other. To get extinction with crossed polars they obviously need to be linear.

I did see a good note on the subject ... if I can find it, I will post it later.

MichaelG.
.
Edit: http://www.ray-optics.com/Polarization_Tutorial.pdf
.
Edit: some of these video demonstations are relevant too:
https://ocw.mit.edu/resources/res-6-006 ... al-optics/
Thanks Michael, I had seen your earlier comment, but not that you had been back and added the URL. I shall have a look now, but in the meantime, a friend has come up with an explanation, which is this;

The device incorporates on one side a quarter lambda plate which 'converts' plane pol. light to circularly pol. light which is not extinguished by the second polar.
If you arrange the polars such that the incoming unpolarised light meets the quarter lambda plate first it then does emerge from the polar as plane pol. light to be extinguished by the second polar in the crossed orientation.

This all seems to make sense, but am still unclear why it needs to be. Hopefully looking at these two refs. will help.

Thanks again for your input.

Mike

Hobbyst46
Posts: 4277
Joined: Mon Aug 21, 2017 9:02 pm

Re: Nikon analyser

#4 Post by Hobbyst46 » Sun Feb 11, 2018 7:33 pm

Perhaps you might like to check Wikipedia as well.

Citation:

Polarizing filter (photography)
(From Wikipedia, the free encyclopedia)

Circular polarizer/linear analyzer[1] filtering unpolarized light and then circularly polarizing the result.

A polarizing filter or polarising filter (see spelling differences) is often placed in front of the camera lens in photography in order to darken skies, manage reflections, or suppress glare from the surface of lakes or the sea. Since reflections (and sky-light) tend to be at least partially linearly-polarized, a linear polarizer can be used to change the balance of the light in the photograph. The rotational orientation of the filter is adjusted for the preferred artistic effect. For modern cameras, a circular polarizer (product labeling abbreviation: CPL) is typically used; this comprises firstly a linear polarizer which performs the artistic function just described, followed by a quarter-wave plate which further transforms the now-linearly polarized light into circularly-polarised light before entering the camera. This additional step avoids problems with auto-focus and light-metering sensors within some cameras, which otherwise may not function reliably with a simple linear polariser.

abednego1995
Posts: 137
Joined: Thu Dec 15, 2016 6:32 am

Re: Nikon analyser

#5 Post by abednego1995 » Sat Mar 24, 2018 9:54 am

There's a depolarizer layer above the polarizer layer (I mean, in the analyzer...) that scrambles the polarization of light in modern microscope analyzers. Since polarizers are not effective for all wavelengths, if you have beamsplitters, prisms above the analyzer you'll have problems because reflective optics are sensitive to the state of polarization. (i.e. slight differences in color at the photo-port compared with the eyepieces.)

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