Crossed polarisation – variable positions of filters relative to each other.
Comparing plain vs crossed polarisation for various samples – all x3.5 magnification as currently this is only objective I have for this microscope – uses special clamp mechanism so my other objectives won’t fit.
For more information on the LOMO Polam P-113 Polarising Microscope, see a wide range of posts at: http://roslistonastronomy.uk/category/microscopy/equipment-for-microscopy/lomo-polam-p-113-microscope
Permian-floodplain-deposit-Robledo-New-Mexico-LOMO-Polam-P113-Crossed-Polars-120518: Excellent birefringement is shown here, and this can be seen varying between the images as polarised filter rotated (below).
Laminated-mudstone-LOMO-Polam-x3-5-plane-polar-120518: Some birefringence evident where crystals form in both images, more so in bottom as the two polarised filters approach 90 degrees orientation to each other (below).
Fossilised-palm-tree-LOMO-Polam-x3-5-plain-polar-120518: Even here some crystal deposition is evident, as shown by coloured areas of birefringence, more evident in second image where polars are crossed (below).
I had a go today at observing a commercial slide of Hydra spp. through crossed polarisation filters on LOMO Polam P-113 Polarising Microscope. The first picture shows the slide with plain polarisation (effectively bright field). The second is where the one filter is rotated nearly 90 degrees. Initially, I thought the bright dots were some birefringence (small bright dots) from the mountant used on the slide, but now I think they are hot pixels on the camera! The specimen interesting becomes nearly invisible – in fact if I rotated to 90 degrees exactly, it did become invisible – this is a little short of that so that you can see specimen in background. Much longer exposure required.
The following photos are from a slide of Ritland Impactite seen through the LOMO Polam P-113 Polarising Microscope. The four photos show the changing colour of the crystals as the polarising filter in the condenser is turned through 90 degrees. There is another polarising filter in the eyepiece assembly. Hence, this slide is being seen with “Crossed Polarising Filters”.
Information on the LOMO Polam P-113 Polarising Microscope can be found here, http://roslistonastronomy.uk/lomo-p-113-polarising-microscope
The following is a video of the same slide through this microscope – showing effect of rotating the polarising filter in the condenser, rotating the rotating stage, and X-Y movement of the stage.