Minimum Aperture

[Don Schaeffer]

https://www.youtube.com/watch?v=y-7nfh-6BPg
Today, in examining the mud puddle, I was beset with focus problems. I could see groups of protists with the stereo microscope and the lower-powered objectives, but I couldn't find them with the high-powered objective. It was frustrating. However when I maximized depth of field by minimizing the aperture on the condenser, I managed to get some reasonable pictures, making bacteria visible as well.