Question

using the bacterial capsule slide, on 100x, is it easier to see the bacteria when the diaphragm is completely open, or mostly closed?

Answer 1

Diaphragm is a part of microscope and is placed in between that of Stage and Condenser. The purpose of diaphragm is to adjust the amount or the intensity of light that enters the specimen. When the aperture of diaphragm is more open, more light enters the specimen and as the aperture remains less open the intensity of light entering the specimen also decreases.

While observing a bacterial capsule slide using 100 X magnification, it is always good to keep the diaphragm mostly closed. It is because, in capsule staining we actually view the capsule as a clear region around the microbe against a black background, ie., we uses contrast. So, when the aperture of diaphragm is reduced it actually increases the contrast of an image that is focused under higher magnification.

Opening diaphragm under higher magnification reduces the quality of the image.