Update October 2018: I had a chance to test the Olympus 5x MPlan FL N against 9 other 5x lenses, you can see the results here in Closeuphotography.com: https://www.closeuphotography.com/5x-lens-test
Olympus MPlan FL N 5x 0.15 Semi-Apochromat Objective
Part Number: 1-U2M522
Official name: Olympus MPLFLN 5x 0.15 Semi-Apochromat Objective
Objective type: Industrial Metallurgical microscope systems
NA, Nominal Aperture, Effective aperture: This lens has a numerical aperture of 0.15, this is a nominal aperture is f/2.7 and an effective aperture of f/16.6
Focal length: 35mm
Parfocal length: 45mm
Working Distance: 20mm
Mounting Threads: RMS Thread
Coverage: Field Number 26.5
Optical system: to use Infinity-corrected olympus objectives for photography, a secondary 180mm (or tube) lens is required for installation.
A detailed test of this objective with side-by-side comparisons of 9 other lenses is available here on Closeuphotography.com: https://www.closeuphotography.com/5x-lens-test
THE BOTTOM LINE
These objectives are available for a little less than the Mitutoyo 5x M Plan APO objectives but I would spend the extra $100 or so for the Mitutoyo and get almost double the working distance and real APO correction.
What I Like
-RMS mounting threads
What I Don’t Like
-Semi-APO correction isn’t anything close to APO correction. Olympus should leave APO out of the model description.
-Not a common tube lens focal length
PRICE AND AVAILABILITY
These objectives are commonly available for about $300-800 on the used market. I paid $300 for a new lens in the box.
MICROSCOPE OBJECTIVE SPECIFICATIONS
Links for More Info
More info at the Olympus USA site: