Question

Which illumination technique is this? The observed feature is not observed in the direct pathway of the reflected light. The feature will therefore be observed against a dark non-illuminated background.

MCQ Options:
a. Direct illumination
b. Retroillumination
c. Indirect illumination
d. Specular reflection

Answer 1

The technique described is 'c. Indirect illumination,' also known as dark field illumination, which allows observation of specimens against a dark background by scattering light.

Step-by-step explanation:

The technique described in the question is known as dark field illumination. This method enhances the visibility of specimens against a dark background by scattering light that does not enter the objective lens directly. The observed feature is seen due to light being diffracted or scattered by the specimen, creating a situation where structures with different refractive indexes can be differentiated based on the levels of darkness. This technique is particularly useful for observing unstained, live specimens, as it increases contrast without the need for dyes or stains. The corresponding option from the student's question is 'c. Indirect illumination.'