Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.
The most effective wavelengths for this use are in the UVB and UVC. Most lenses (except the very few ones designed for UV imaging and a handful more) transmit little to no UVA, and no UVB and UVC, so exposing these lenses to UVB and UVC has no effect on fungus located behind the outermost front and rear optical surfaces.
Formaldehyde (gas) is a classic for sterilizing microscopes and, some decades ago, even entire rooms. See for example:
- Suzuki A and Y. Namba, 1982. Sterilization of operating microscope and flexible fiber-optic illuminator by formaldehyde gas. Nagoya J. Med. Sci., 45, 43-48.
- Tayler, A.L. et. al., 1969. Paraformaldehyde for Surface Sterilization and Detoxification. Applied Microbiology, (17)4, 614-618.
Not really effective, unless the objective is optimised for UV. Oly as I'm sure you're aware marks theirs with 340. I might be purchasing a 10x oly apo infested with shrooms, seller quoted $150 and he's happy to test it. Not sure how I'll deal with those pesky shrooms.