the fact that both Martin and I show pictures of Cyanobacteria under polarized light is pure coincidence.
Since my new scope has POL contrast it is quite understandable that I am playing around with it.
This shows the birefringent cellwalls of a green algae under polarized light. Notice the cyanobacteria sitting on top of it. When I looked at the image I was wondering, why is there no dark background? So I switched the condensor from brightfield to darkfield.
Amazingly now the cyanobactera turned red.
This is a larger cyanobacteria (oscillatoria?) that I accidently crushed.
Of course I had seen pictures of algae fluorescence and this looked familiar. But here we have just a darkfield with POL. This effect is only present with cyanobacteria and there is no red in green algae.
I have tried this with 3 different kinds of cyanobacteria - they turn red. Maybe it is related to the different chlorophyll, I don't know.
Can anybody explain this effect?
I hope you enjoy the pictures as much as I do.
Ecki