The Latest Information about SW Filters
Some important information about SW filters (ultraviolet-transmitting visible-absorbing filters) the Hoya U 325C and UL254S.
My company UV SYSTEMS, Inc. has been a customer of Hoya Corporation USA-Optics Division for over twenty-three years. I have worked with more than eight managers during that time and even visited their facilities twice. For all those years I have ordered their U 325C filter in wholesale quantities to obtain the lowest cost.
When Hoya announced in April 2019 that they were not going to take any new orders for their U 325C filters I and many of the FMS members were concerned. Later in October 2019 they changed their minds, and I placed a very larger order for some of those U 325C filters. Then in 2020 Hoya announced that their UL254S filter would replace the U 325C filter. The U 325C filters have always been molded with a nominal thickness of about 4.5 mm thick with one side smooth and one side rough. The new UL254S filters are made a different way (and possibly a new formulation) into a large block and then they cut the filters to the size desired and polish both surfaces. The UL254S filters are only 2.5 mm thick and therefor have a higher initial transmission at 253.7 nm (SW) than the U 325C filters. Based on recent measurements of four U 325C filters they have an average initial transmission of 54.1% at 253.7 nm, while one UL254S had an initial transmission of 70.9%. Since they have a difference manufacturing process and must polish both surfaces of the UL254S Hoya announced that those filters would be more expensive than the U 325C filters. Obviously the larger the quantity of filters ordered the lower the cost per square inch.
UV SYSTEMS is planning on doing a solarization test on the one UL254S filter it has and compare it with four U 325C filters at the same time. No completion date for that test has been scheduled.
In November I sent Hoya a request for quote for wholesale quantities for both the U 325C and the same quantity of UL254S filters to compare the cost per square inch. Here are the figures based on a cost per square inch:
The increase in the U 325C smaller size filter from Oct. 2019 to Nov. 2020 = 23.05%
The increase in the U 325C larger size filter from Oct. 2019 to Nov. 2020 = 21.99%
The increase in the UL254S smaller size filter over the U 325C filter = 226.01%. (3.26 times more)
The increase in the UL254S larger size filter over the U 325C filter = 190.27%. (2.90 times more)
The small size filter is 11 square inches. The large size filter is over 24 square inches.
As far as I know Hoya still has a $300.00 minimum order requirement.