Maximum resolving power and depth of focus for a visual microscope

objective focal length (mm) numerical aperture (N.A.) maximum useful magnification in compound microscope maximum resolution on object (mm) objective depth of focus (mm)

32 0.10 100× 0.0025 0.025

16 0.25 250× 0.001 0.0038

8 0.50 500× 0.0005 0.00086

4 0.95 1,000× 0.00026 0.00024

3 1.38 1,500× (oil immersion) 0.00018 0.00010