So I want to run an experiment with yeast. I want to monitor the population as close as possible in regard to its size. I am aware I could use a colorimeter or such, but I can only get a microscope. Is there a way I can estimate the population with a microscope?
Determination of cell concentration using a microscope is usually done by using a hemocytometer, also called counting chamber or Neubauer-counting chamber.
Basically, you count the cells in a defined volume within a specific area. This way you can calculate the concentration in your medium and also the total cell count.
I found a good explanation especially for counting yeast cells here.