I was working on some images on Capture One pro and then I had a thought. How about looking at the infrared (IR) suppression capabilities of some of the UV-pass filters I have. I do have the Baader U 2011 version, the latest 2013 Baader U version which is said to have better IR suppression than the previous models. Also, I thought I would test my U340 1mm + S8612 1.5mm stack for comparison.
Camera: full spectrum Olympus OMD EM-5
Lens: Coastal Optics 60mm F4 APO
Settings: ISO 200, 1/100 sec, F4 or F11 aperture
UV-blocking/IR-passing filter: 3mm thick RG665
Light source: Quantum X2D 1/1 power
Subject: Sintered PTFE disc
Anyway, here are the results:
For reference, this is what my highly UV & IR-reflective subject lit by 1/32 power Quantum X2D looks like (5.0 EV less light required compared to the f11 IR-suppression test images)
Baader U 2011
1) The latest Baader U 2013 version has more IR-suppression than the other two filters. The f4 image just about shows a tiny part of the sintered PTFE lit by IR.
2) At the settings needed to produce the reference UV image ISO 200 f11, there was no visible IR leak seen with any of these filters even when lit by an extra 5 EV of IR-light from the Quantum X2D (compared to the reference image).
3) Latest Baader U performed best for IR suppression, followed by the Baader U 2011 and then the U340 1mm + S8612 1.5mm UV stack.
So those who say there is IR-leak in their images taken with the filters tested above need to look again, as this should not be visible in real life situations (unless you are specifically testing for it). Hence they should be useful for UV-imaging, assuming your equipment are up to it. Clearly if you have a poor UV-transmitting lens coupled with a camera with poor sensitivity to UV but great IR sensitivity, then perhaps the Baader U 2013 would be your safest bet for UV-imaging.