Let's set the story straight. The maximum magnification you can get on a standard light microscope is about 1250x to 1400x. This is viewing through the eyepiece with the naked eye which will also give you the finest detail you can see. This detail is termed resolution. Useful magnification is a function of resolution.
Resolution is the limit up to which two small objects are still seen separately.
It is used as a measure of the resolving power of a microscope. A 100x oil objective typically can have a numerical aperture of 1.3. When a microscope is sold based on some ultimate magnification factor like 8,000x or 30,000x, this is simply related to the physical image size that appears on the video monitor. For example, a red blood cell is 7 to 8 microns in diameter. So a I inch red blood cell on the video monitor is magnified 3175x.