Binocular microscope use, diaphragm? I am try to review my scope work, since my proffesor asked me to calibrate all the scopes for an intro class in biology, and it has been awhile since I used one. I googled "Binocular microscope use" and saw a powerpoint as my first link. On page 21 it stated: > The diaphragm should be opened just enough to allow the objective lens to collect all of the light that comes through the sample. Opening the diaphragm too wide, allows some of the light to escape collection by the objective lens. Closing the diaphragm too much, causes aberrations of the image. **But if the diaphragm controls the amount of light passed through, why is "light escaping" a bad thing? Why cant I keep the light as wide as possible?** As an aside, if anyone has any suggestions for review on binoc. compound microscope use, I would appreciate it.

The escaping light causes unnecessary illumination, thus reducing the contrast. This webpage has a couple of photos that demonstrate different microscope setups.