A strew slide of Amphipleura pellucida, from Berrow, Somerset, UK. Material collected by Klaus Kemp. Slide was prepared by Horace Dall. Dated 1982, shadowed with aluminium in a vacuum. Standard brightfield illumination gives a darkground image with full NA even for a high NA objective. Olympus BHB microscope using 365nm LED light (450nm for the 10x image image). As well as the wider field of view image, I photographed a couple of individual diatoms using 365nm light. 63x Leitz Pl Apo 1.4, oil immersion. Olympus Abbe condenser, oil immersion, brightfield lighting. 2.5x Nikon CF PL photoeyepiece. Monochrome converted Nikon d850 camera. Single unstacked images. One one the striae were measured with a spacing of 286nm. On the other, the puncta were just about visible and had a spacing of about 244nm. The puncta were more visible at a different focus depth to where the striae were most obvious. Measurements were done in ImageJ.
Amphipleura pellucida (Kützing) Kützing 1844. Published in: Kützing, F.T. (1844). Die Kieselschaligen Bacillarien oder Diatomeen. pp. [i-vii], [1]-152, pls 1-30. Nordhausen: zu finden bei W. Köhne. Page 103, Plate 3 Figure 52, Plate 30 Figure 84.
Horace Dall is a bit of a hero of mine as he was an optics genius, and these metal coated slides are really interesting given the ability to use relatively simple imaging to resolve and image really tiny details.