H.S.E Test Slide

Transmitted Darkfield Illumination

Definition/Function:

The Phase Contrast Test Slide is manufactured to test the sensitivity of a phase contrast microscope to a given shift in phase between the direct ray and the diffracted ray paths for a specific configuration of the microscope. This slide is designed to test sensitivity to phase and not the resolution limit or limit of visibility for the microscope. This photograph shows that the groups of groves are clearly visible using a 10X objective, NA 0.25, using darkfield illumination.

Significance in the Environment:

This slide has been represented incorrectly by some as a test of the resolution limit of the microscope in a given configuration. It is evident from this photograph taken with an objective that has a resolution limit of 1.9 micrometers that visibility and resolution are not the same. The first set of lines are below the resolution limit of the 10X objective but even the seventh set of lines is visible using darkfield (dark ground) illumination. Particles only tens of nanometers are visible with the light microscope but if two such particles are side by side only a difference in brightness is seen; the particles themselves can not be resolved.

Characteristic Features:

The pattern on this slide consists of seven bands of twenty lines each. The width of the individual lines range from 1.1 micrometer for the first set to 0.25 micrometers for the seventh set of lines. The depth of each engraved line from which the resin cast is made is approximately one tenth of the line width. The refractive index of the resin used to make the cast is 1.58.

Associated Particles:

References:

LeGuen, J.M.M., T.L. Ogden, T. Shenton-Taylor and J.F. Verrill, The HSE/NPL phase-contrast test slide", Ann. Occup. Hyg., Vol. 28, no. 2, pp. 237-247, 1984

http://www.proscitech.com.au/cataloguex/get_notes.asp?S8084 This reference briefly gives some of the specifics on the design of the test slide.