difficultdiatoms are resolved without the need for toxic mountants. Using light microscopy, almost all diatoms are better visualized using oblique or DIC(NIC) illumination, although darkground and phase contrast can also help in some cases. In order to get the results shown below, the user must understand how to properly adjust the condenser, aperture diaphragm, field diaphragm, and orientation of off-axis (oblique) illumination. The following images are enlarged to show details and they are not all the same scale. They were all taken with a Amscope 5.1 MP model MU503 camera using Amscope software.
DIATOM | OBJECTIVE ILLUMINATION | STRIAE RESOLVED | PUNCTA RESOLVED | COMMENTS |
G.balticum | 20X oblique | DISTINCT | WELL | Good Diatom for 20X |
N.lyra | 20X oblique | FAIRLY WELL | POOR | Striking diatom at 40X |
40X oblique or DIC | DISTINCT | DISTINCT | ||
S. phoenicenteron | 20X | DETECTED | POOR | Difficult striae at 20X but striae and puncta resolved at 40X. |
40X Oblique Illum. or DIC | DISTINCT | DISTINCT | ||
N.Sigma | 20X Oblique Illum. | POOR-just barely seen | ABSENT | The striae of this diatom are not visible at 20X and are fairly resolved with proper DIC illumination at 40X as are the puncta; oblique illumination at 40X worked also, but not as well as DIC. This is a diatom where the visual resolution was clearly better than the photograph. |
40X Oblique Illum. | FAIR | GOOD | ||
40X NIC | FAIR TO GOOD | GOOD | ||
100X | GOOD | DISTINCT | ||
S.gemma | 20X | NONE | NONE | The striae of this diatom are not visible at 20X. Striae can be resolved at 40X. Puncta require 100X. |
40X | GOOD | NONE | ||
100X DIC OR OBLIQUE | DISTINCT | DISTINCT | ||
P. angularum | 40X | DISTINCT | DISTINCT | Pleurosigma angularum has long been a favorite diatom of users of the microscope. It is not resolved at low powers. At 40X both the striae and puncta are clearly resolved, but not at 20X. 100X objectives reveal the walls of the puncta. |
100X | DISTINCT | DISTINCT | ||
F. rhomboides | 40X | DISTINCT | NONE | F. rhomboides reveals striae at 40X but puncta require 100X. |
100X | DISTINCT | DISTINCT | ||
A. Pellucida | 40X | NONE | NONE | The most difficult to resolve diatom on the Kemp slide and cannot be resolved without 100X and even then requires both mounting on the coverslip and very high refractive index mountant (refractive index over 2) along with extremely oblique illumination and/or DIC. |
100X | GOOD ONLY IF MOUNTED ON COVERGLASS | NONE | ||
100X WITH VERY HIGH R.I. MOUNTANT(OVER 2.0), WITH COMBINED OBLIQUE AND DIC ILLUMINATION | GOOD* | FAIR* |
OBJECTIVE | SUGGESTED | MORE DIFFICULT |
20X S-plan n.a.0.46 | G. balticum Puncta | S. phoencenteron Striae, N. Sigma Striae. |
40X S-plan n.a. 0.70 | N. lyra & S. phoenceteron Puncta | S. gemma Striae, N. sigma puncta |
100X S-plan Apo n.a. 1.35 | Puncta of S. gemma & F. rhomboides | Striae and Puncta A. Pellucida* |