What are the parameters to choose a good objective
What is the strehl ratio?
Screw type
RMS (Royal Microscopical Society objective thread)
M25 (metric 25-millimeter objective thread)
M32 (metric 32-millimeter objective thread).
Less common or older
M27 x0.75
M27x1.0
Working distance
Immersion
Numerical aperture
Optical Correction
Transittance
Others
Tubelength
Adjustment