Moderators: rjlittlefield, ChrisR, Chris S., Pau
Really nothing different from a quality filter you might use on any high quality lens. Flat overall, and with plane-parallel surfaces that have very flat smooth surface qualities. That will minimize image degradation.Charlie, what are we looking for, as far as a pol filter that's more/less likely to work as an analyzer?
... and had it mounted in a frame that provided a flatter surface than I had. So perhaps I was too hasty and strong in my comments about using the Edmund material. The piece I used was not held as "flat" as is possible. I should try it again with a better frame/holder. And it is entirely entirely possible that the optical ("imaging") characteristics from 3D glasses he tried are better than the piece I used.I tried about a dozen different 3D glasses until I found one that had very good clean flat thin plastic lenses.
NaCl is one of the less interesting minerals under cross pol because it belongs to the cubic system, the only one whose crystals aren't birrefringent.DaveBH wrote:Sea salt ...
For those who might be reading this as "lurkers"... you can use a camera "CPL" (circular polarizer) for this, just be sure that it is oriented so the the side that would normally face the subject (away from the camera lens) is the side that is facing the subject on the microscope stage. This is true for both the lower ("polarizer") and upper ("analyzer").Then I put a generic CPL over the light source
Just to add some points:chrismower wrote:On a general note there are two types of polariser lenses that are in common use with cameras, linear and circular polarisation. Linear polarisers were used with film cameras and circular polarizers are used with modern digital cameras.
I have had very good results with both types but they do behave slightly differently when used on a microscope. I find that linear polariser/analyzer combination gives a better extinction. The polarizer film in cinema 3D glasses is, I think, linear pol but I can't guarantee it.
Another thing is that total extinction is not always needed as you can get some very interesting effects when just rotating the bottom polariser if the subject has any polarising characteristics.
Mostly true. In theory, a linear polarizer can also interact badly with the anti-aliasing filter on a digital sensor, since that often uses birefringent materials to spread the light. I don't recall seeing an experimental demonstration of this effect.Pau wrote:- Circular pol were implemented before for AF film cameras. They are linear pol with a quarter wave plate at the camera side because linear polarised light may fool phase AF sensors and circular polarised light does not, nothing directly related to film vs digital.
As a lark, I purchased some polarizing film from a local science store, made a polarizer and analyzer using black card stock and a jar lid. Unfortunately, I didn't know about color neutrality so there's a strong blue cast to all my photos with it - Maybe I'll try it again with the filters you suggest.Charles Krebs wrote:Jim,
Very "doable" with your budget".
If you are looking at microscopes and already know that cross-polarized lighting is a primary interest then it makes sense to keep an eye out for one that allows insertion of a polarizer ("analyzer") somewhere above the objective but before the eyepieces. This is not absolutely essential but it does make cross-polarization easier. Such microscopes are far less common than those without such a provision, but it doesn't hurt to keep it in mind when looking.
I will also strongly recommend Edmund Optics Techspec polarizing film:
http://www.edmundoptics.com/optics/pola ... -film/3435
The color neutrality and extinction ratio are excellent. It seems to provide results as good as my Olympus microscope polarizers. I use it over the base light "port", but not in the image path. In the optical path I stay with an Olympus microscope polarizer. (But I have been meaning to "test" a piece of this material in the optical path. At 0.18mmIt it is pretty thin so it might do better optically than expected. Since it can be easily cut to size, it would often be far easier to implement than a "glass" filter. If I ever do this test I'll add the results to this thread).
