Microscope focusing problem?

she should adjust the diaphragm setting. the diaphragm is located under the stage (some microscopes have a condenser lens mounted above the diaphragm, visible through the hole in the stage where the light comes through from the light source)

usually she would have to close down the diaphragm to diminish the volume of light that is being transmitted to the specimen being viewed. by closing down the light there is a better contrast of light passing through the cellular components.

she should also have prepared the onion root tip with a stain( iodine or methylene blueare ideal). these stains would have enhanced certain cellular components(such as membranes and nuclear material) as they would have differentially absorbed the stain thereby enabling the observer to discern them

It sounds like the irus diaphram was not open sufficiently. You often close it down when working at low power but you have to open it when working at high magnification, to let enough light through. There could be such a diaphram located on the illuminator, and/or one located in the condenser just below the stage. Another cause of the problem could be the condenser being too far below the stage. Also, some condensers have an additional swing-in element that is swung out for broader illumination at low power, but has to be swung back in for high power illumination. Also make sure there are no filters in the light path like neutral density filters or polarizers.

The magnification of the compound microscope is the product of the magnifications produced by the objective lens and the eye lens. In the normal adjustment the final image is formed at the least distance of distinct vision D ( from the eye lens) which is 25 cm for a normal eye. M = Me x Mo As the eye piece acts as a simple magnifying glass , its magnifying power is Me = ( 1 + D / fe ) fe = 8.4 cm D = 25 cm If v and u are the image and object distances from the objective lens, the magnification produced by it is Mo = v / u 1/ v + 1 u = 1 / fo Mo = v / u = (v / fo ) - 1 M = ( 1 + D / fe ) ( v / fo - 1 ) fo = 3.3 cm v can be calculated as v = ( L - D fe / (D + fe )) L = 25.5 cm is the separation between the objective and the eye lens. v = 19.2 cm M = 19.43

maybe it's all about the light source. she must be sure that she gathered enough light so it would be clear. or the problem might be on the microscope.