Saturday, October 12, 2019

On Chinese ZWB1, ZWB2, ZWB3 filter problems for reflected UV photography

Today about Chinese UV (ZWB1, ZWB2, ZWB3) filters intended for reflected UV photography. Those seem to be attractive, since the offered prices for instance on the portals ebay or Alibaba are far below the prices of such filters made from original SCHOTT or HOYA filter glass, both world renowed glass makers. I bought several ZWB1, ZWB2, ZWB3 filters for testing and two of them showed some effects worth knowing of, which I have never seen with Schott or Hoya filter glass.

[click on image gets you a larger image]

Here some examples shot in reflected ultraviolet (UV) light. UV filter used on my multispectral camera for reflected UV photography was a stack of Schott UG11 + S8612 ionic glass filters. A 365nm UV LED light was the light source. Background was a white 100x100mm Spectralon (R) calibration target.

These both were ZWB2 filter glass which its equivalent is SCHOTT UG1.

82mm ZWB2 filter in reflected UV (365nm)
52mm ZWB2 filter in reflected UV (365nm)
It gets quite visible that some very prominent striae, as defined in the International ISO 10110 Part 4 standard are prominent in these two samples. This in my opinion based on lack of suitable or careful enough Quality Control (QC) of the Chinese glass manufacturer (this maker here unknown) and may possibly occur in all those black glass filters, as it needs special equipment to do QC-checking using transmitted and reflected UV light.

Let me be very clear: I'm not stating that these issues will always be there or how likely these issues will be, as I have no data on this. Just be careful and test out your filters! For my part I will stay with SCHOTT or HOYA filter glass, as I never had any issues like that...

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site