An interesting pair of slides. Pleurosigma formosum var. longissima, single example on each. One is mounted in Styrax, the other Hyrax. Both slides are very thin – about 0.6mm thick. No name, but these are by Samuel Henry Meakin. Olympus BHB microscope using 450nm LED light.
Initially I just imaged both using a 10x Nikon Plan Apo NA 0.45 objective, Olympus Aplanat Achromat condenser, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Single images. Processed the same. The final comparison demonstrates the much more contrastry image with the high refractive index Hyrax mountant, compared with Styrax. Note – Meakin’s handwriting. ‘St’ looks very much like ‘H’…..
Then I imaged the one mounted in Hyrax using a 20x Nikon Plan Apo NA 0.65 objective. Olympus Aplanat Achromat condenser, oblique lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. 41 images stacked in Zerene (Pmax). A nice high contrast image. I also inverted it to give a pseudo-darkground effect. The high contrast original was especially good for this. One big diatom – 614µm long as measured in ImageJ.
Pleurosigma formosum var. longissima Grunow in Cleve & Grunow, 1880. Original description: Cleve, P.T. ; Grunow, A. (1880). Beiträge zur Kenntniss der Arctischen Diatomeen. Kongliga Svenska-Vetenskaps Akademiens Handlingar. 17(2): 121 pp., 7 pls. Page 48.