As the senescent cells will be stained blue you will only need a normal brightfield microscope; phase contrast can be useful, however often even unstained cells can take on a slightly blue tinge because of the refraction, which can make it difficult to differentiate between stained and non-stained cells, so a normal transmission brightfield microscope will do.

There's only one staining technique published / and commercially available for staining of senescence associated beta gal activity which is chromogenic and blue in appearance. Of course you can use either an upright or inverted microscope depending on the vessel you cultured your cells in. The question was whether wide field brightfield or phase contrast microscopy was needed in addition to special filters... Upright or inverted microscopy has nothing to do with illumination technique...

Thanks Axel and Aleksandra, this is very helpful. I will post the images after the experiment.

For reflection, for a specific tissue cells use dye dab heamatoxin to observe the internal structures of the cell if either patients or infected tissue there are other ways to observe the cells