OLYMPUS MPLAN FL N 5X OBJECTIVE
The 5x M Plan FL N which is my first olympus objective has been tested at 5x against 9 other lenses, you can see the test here in Closeuphotography.com:
https://www.closeuphotography.com/5x-lens-test
Also I posted a page with more details and specs on the lens here on the site:
https://www.closeuphotography.com/olympus-5x-plan-semi-apochromat-objective