Olympus SC30 User Manual page 40

Appendix I: Microscope settings
Useful
magnification
Empty
magnification
You can determine the total magnification by dividing the length of the object
shown by the set length on the micrometer. The useful magnification of the
optical systems microscope depends on the numerical aperture of the objective
being used (engraved on the objective). The useful magnification is in the range
of 500x to 1,000x the numerical aperture.
A loss of contrast and sharpness is the result if total magnification is larger than
the useful magnification. Check to see if replacing the TV adapter with a 0.5 or
0.63 model sufficiently reduces the total magnification. If this is not possible, you
can also use an objective with the same magnification, but with a higher
numerical aperture.