Podosira Stelligera (?) Gegenüberstellung BF / POL

[sushidelic]

Hallo,

hier ein Proband aus einem Präparat von Anne mit primär rezenten Gyrosigma Balticum, aber auch einigen anderen interessanten Spezies.
Mir fiel diese Diatomee deswegen auf, weil ihr Zentrum bei gekreuzten Polfiltern heftig aufleuchtete.
Aus Interesse schoss ich zweimal einen Stapel, einmal Pol, einmal Hellfeld mit Blaufilter (Schot PIL-1).
Interessant ist der Auflösungsgewinn im Zentrum. Beim Pol-Bild sind quasi nur noch Beugungsartefakte zu sehen, während das Hellfeld mit Balufilterung (ca 460nm?) die Struktur doch plausibel auflöst.
Die Kieselalge hat einen Durchmesser von ca. 57µm. Beide Bilder wurden vor schwarzen Hintergrund gesetzt, beim Pol-Bild war er logischerweise schon vorhanden, beim Hellfeld habe ich ihn einfach heruntergezogen.

Durchlicht:

Pol:


LG Michael

[Rene]

wow, that's great stuff. Podosira stelliger indeed (although a taxonomical name change to Hyalodiscus is to be expected).
It's always tricky to interprete structure at the diffraction limit. I've showed something similar before in the areolar structure of Hyalodiscus scoticus, between BF and DIC: http://www.mikroskopie-forum.de/index.php?topic=27888.msg209073#msg209073

Best wishes, René

[sushidelic]

Hi René,
sure I do remember your comparison that I read with great interest, and which complies with my results for a similar test - even using the DICHR, the maximum resolvable detail was less than with brightfield/oblique lighting. I have to admit, that I didn't have the oiled top lens u-tlo for the condenser, but that was also the case for the brightfield setup. Once I have my U-TLO in the hands (it's on its way from the US), I will dig into it again and repeat your test with maximum aperture:). DIC just looks great though, and is pain in the a.. for stacking.
The pictures in this thread were made using a crude combination, as the only "oil" condenser at my disposition was a BH series phase contrast turret with na 1.25. No clue if that is optically correct in a BX setup, but I was able to achieve Koehler illumination and it fitted into the tray.
Another interesting detail is "cell" structure, that reads really different in Pol and DF.
Apparently, I haven't done justice to the Pol image, as using a blue filter is changing the game. So here's a crossed pol with the blue filter in place. Resolution is better, but still not catching up with the BF.