System 273/373 vs. System 250 Microscopes

What differentiates a System 250 microscope from a System 273/373 microscope?  How do their working distances compare?  Which has greater magnification and greater field-of-view?
Greater working distance
System 273/373 Microscopes have nearly 8" working distance (when used with a 0.5X reducing lens). 

system-273-and-373-vs-250-working-distance-1_edited system-273-and-373-vs-250-working-distance-2_edited
 System 273/373 System 250

Greater magnification
Optical magnification:
    System 273/373: Maximum magnification: 270X
    System 250: Maximum magnification: 225X

Greater field-of-view

system-273-and-373-field-of-view system-250-field-of-view_edited
 System 273/373System 250

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