UV transmission filter

Though an UV filter which has transmission shorter than 300nm is not common
for ground-based telescopes, an inquiry about such "UV transmission filter" from
astronomers who are involved in space astronomy are nowadays increasing,
e.g. for the ULTRASAT in Israel or the STAR-X in the United States.

It is technically very hard for any vendors to coat an UV filter that has transmission
below 300nm and blocking ~ 1000nm simultaneously due to the property of UV
coating material.

Asahi succeeded in producing the optical blind UV filter for the PETREL ordered
by Tokyo Institute of Technology in 2021.
Maximum 180mm diameter UV filter is currently available.
figure optical blind UV filter for PETREL