A different look at some plankton subjects

[Charles Krebs]

Dragged the plankton net again. I haven't found anything very different yet, so I decided to take a different "look" at some of the more common subjects collected.

The planktonic mollusk larvae really show nicely under polarization.

For this first one I did not cross the polarizers to extinction, which left the background a dark charcoal gray. (It would have been easy to pull this down to black in post, but I sort of prefer the dark gray). These shells are so tiny, yet they look very much like their much larger relatives. Photographed at 42X on sensor.




These bivalves (below) make a nice abstract pattern. The polarizers are fully crossed, so the background has gone completely black The polarized light provides nice colors along the edges. Photographed at 82X on sensor.



If you want a real recipe for frustration, try photographing live diatoms with an oiled darkfield condenser and an oiled 100X objective... when your condenser carrier has gotten a little loose and it slowly drifts down.
(gonna have to tend to that tomorrow!)

There's so little DOF, and the non-focused areas go hugely blurred. But is can make for an "other-worldly" look. The next three were photographed at 208x on sensor.

There are no scale bars included, but the field size represented in each shot is 0.0043 x 0.0028 inches (0.11 x 0.07mm)





This last shot shows some interesting detail on the surface of a dinoflagellate. Don't know the species but it was a deep red/orange color. The specimen was intact, the orange "cloud" to the right is simply a result of the subject color and the out of focus effect you often get with high NA darkfield illumination.

[Franz Neidl]

Hello Charles,
an interesting experiment. I like the first picture and I have two questions:

1. When you make pictures with polarization you keep the Wollaston-Prisma (from DIC) in the microscope? Or are you using exclusively polarisation filters (linear or circular)?
2.

Dragged the plankton net again. I haven't found anything very different yet,

Are you still using the plankton net with 153 micron mesh or have you allready one with 60 micron mesh? (Sorry for this indeescrete question, but with a 60 micron net probably you will find more...).

Franz

[Charles Krebs]

Franz,

Very basic polarization. I use the polarizer (linear) built into the DIC condenser, turret is in normal brightfield position (the DIC prism is not in the light path). I use a linear polarizer in the upper piece (instead of the DIC slider).

I still use the 153 micron mesh. I would like to try a smaller mesh. The thing is, I get so much now (mostly two or three species of diatoms) that it is very hard to look through it! There likely are interesting specimens in there, but it's like looking for a needle in a haystack. And I suppose some interesting creatures do slip through the 153 micron mesh. I probably need to develop better pipettiing skills, use the "search" stereo at a higher magnification, and try some other geographical locations with the net.

[Franz Neidl]

Hello Charles,
thank you for your answer. I am always learning from you. Thank you for sharing your experience!

but it's like looking for a needle in a haystack. And I suppose some interesting creatures do slip through the 153 micron mesh. I probably need to develop better pipettiing skills, use the "search" stereo at a higher magnification

I dont have a stereo microscope (and a 153 micron net) therefore I use other methods to concentrate the sample (to reduce the "haystack").
Currently I use a tea-filter. Personally I like it very much, because it works very fast.
Before I used a champagne glas. For the sedimantation I had to wait longer.

Franz