Good (Vis/NIR) microscope optics go up to f/0.56 (NA 0.9) without oil immersion. Granted, such an objective will cost you 3.5k$ [0], but they don't go to these lengths without expecting near-diffraction-limited performance.

[0]: https://www.thorlabs.com/thorproduct.cfm?partnumber=RMS60X-P...