Diatoms

[Macro_Cosmos]

99 of these put in a circle!
Cross polarised, Dmap, 10x oly.

[Pau]

...
Cross polarised, Dmap, 10x oly.

The image doesn't look cross pol at all, it seems like bright field, could you clarify your technique, please? (partial crossed pol, Xpol with 1/4 plate...)

Excellent slide and very well imaged, BTW

[Macro_Cosmos]

...
Cross polarised, Dmap, 10x oly.

The image doesn't look cross pol at all, it seems like bright field, could you clarify your technique, please? (partial crossed pol, Xpol with 1/4 plate...)

Excellent slide and very well imaged, BTW

Weak polarisation but I can assure you that it's cross polarised. I suppose that's the partial cross polarisation you refer to? With normal brightfield, I've found out that the colours aren't as vibrant.
I'm using an EO glass polariser placed behind the nosepiece and film polariser for the condenser, Saul's 3D printed holder holds it in place and allows adjustments.

[Pau]

Weak polarisation but I can assure you that it's cross polarised. I suppose that's the partial cross polarisation you refer to?

Yes, this seems what is called partially crossed pol. Crossed refers to the maximum extinction of light with no sample, period
Parallel polarizers is at 90º of crossed, any position in between are partially crossed

Diatoms silica sells are amorphous so in most cases they show no birrefringence and under crossed polars they look just black

[Macro_Cosmos]

Weak polarisation but I can assure you that it's cross polarised. I suppose that's the partial cross polarisation you refer to?

Yes, this seems what is called partially crossed pol. Crossed refers to the maximum extinction of light with no sample, period
Parallel polarizers is at 90º of crossed, any position in between are partially crossed

Diatoms silica sells are amorphous so in most cases they show no birrefringence and under crossed polars they look just black

That does make sense actually. However generally I see the use of 2 polarisers being called "polarised light", I suppose it doesn't necessarily imply full XPL at maximum extinction.
At maximum extinction which is only 100:1 for my economic glass polarisers, simply increasing the exposure as expected show colours, but the result is weird. Colours are off and disturbing to me. Without the polarisers, the colours don't look as nice. Maybe it's the colour shift brought in by my cheap polarisers creating this effect.

I have high quality ones coming, stuck in the warehouse due to the second wave of covid. I'll spare everyone from my rant on incompetent government policies...

Hope my 20x shipped using DHL comes to me soon. At 10x, I'm wasting at least 80% megapixels for this arrangement.

[Pau]

...However generally I see the use of 2 polarisers being called "polarised light", I suppose it doesn't necessarily imply full XPL at maximum extinction.

Just to clarify some concepts:
- With just one polarizer you have polarized light. With two you can play with the angle of the analizer relative to the polarizer.
- Again, crossed are crossed only when crossed, with the polarization plane of the light of both filters perpendicular. This is not my opinion but a well established principle.

With a 20X you can expect more resolution (if its NA is bigger than the 10X, of course) and smaller field but when you increase resolution the interference colors of the diatom shells tend to disappear, typically with a 40X all are gone

[Lou Jost]

Very micely done. I wish I could find "big" diatoms like those. Mine are barely visible even at 50x.

[Macro_Cosmos]

...However generally I see the use of 2 polarisers being called "polarised light", I suppose it doesn't necessarily imply full XPL at maximum extinction.

Just to clarify some concepts:
- With just one polarizer you have polarized light. With two you can play with the angle of the analizer relative to the polarizer.
- Again, crossed are crossed only when crossed, with the polarization plane of the light of both filters perpendicular. This is not my opinion but a well established principle.

With a 20X you can expect more resolution (if its NA is bigger than the 10X, of course) and smaller field but when you increase resolution the interference colors of the diatom shells tend to disappear, typically with a 40X all are gone

Yep, all colours are void at 40x, so might as well use a green interference filter for the best image quality.

I have a shot at 100x too, the interference colours are pretty much desaturated, B&W ends up looking better.

Very micely done. I wish I could find "big" diatoms like those. Mine are barely visible even at 50x.

I heard it really depends on location. There are some places with rather large diatoms, I've even heard claims of ones covering a fullframe sensor at 10x, which implies the thing is around 2.4mm! Now that's visible to the human eye for sure.

I'm gonna consult some diatomists on equipment necessary to make these slides. For starters, I think I'll need a somewhat decent centrifuge and a "clean room" kind of benchtop setup to make high quality slides. Even Klauss' slides contain dust and fibres. Some very high quality vintage slides are however (expensive) very clean. If someone in 1900 can do it, so can I.

[Lou Jost]

Do you know what kind of environment these diatoms come from? Are they aquatic or terrestrial? Maybe that has something to do with size.

[hkv]

That is a very nice set of diatoms! Always amazing to see how much variety there is among diatoms.

[Macro_Cosmos]

Do you know what kind of environment these diatoms come from? Are they aquatic or terrestrial? Maybe that has something to do with size.

Unfortunately not. Maybe someone can identify those diatoms. They are prepared for rather "artistic" purposes.
Stefano from diatomlabs sell prepared slides where the diatoms are mounted directly under the coverslip for the best image quality.
http://www.diatomshop.com/buy-now.html
He does provide ID and origin for these diatoms. All I know is that diatoms come in nice shapes, and they are important, and they can survive even the worst environments.

Actinoptychus heliopelta from Dunkirk, Maryland, USA, for example can be rather large. I'm going to buy some slides from him for photomicrography in the future.

[Lou Jost]

Actinoptychus heliopelta from Dunkirk, Maryland, USA, for example can be rather large.

Do you know if that would be a terrestrial one or an aquatic one?