B+W IR Dark Red (092) filter query

[Ashfaque]

Hello,

Is B+W IR Dark Red (092) filter equivalent to (or, 'read closer to') Heliopan's RG 715 filter (715 nm), or RG 645 (645nm) filter? I'm a bit confused after reading B+W descriptions. I'm guessing it's closer to RG 715, but I just want to make sure.

Also, where does those numbers in bracket (092, 093, etc.) come from? I noticed those numbers are different from Kodak's Wratten ones.

Bests,
Ashfaque

 

[MartinCrabtree]

I think the 092 may mean sensitivity above 920 nm?

 

[DWThomas]

In the case of B+W, I believe the numbers are "just numbers." I have a PDF file of a B+W brochure that says the 092 is approximately equal to an 89B.

"blocks visible light up to 650 nm, and passes only 50% of the radiation just below 700 nm (thus the dark red color). From 730 nm to 2000 nm, transmission is greater than 90%. This makes photographs of pure red and infrared images possible with the best utilization of the relatively low sensitivity of infrared films."

All that description isn't much help because one has to know the definition of "cutoff." However passing 50% is a loose description of how other (electrical signal) filters define cutoff so it sounds as though this would be a 700nm. Elsewhere I've seen the 89B described as a 695nm cutoff, so that would be consistent. (I'd expect it to work pretty well with today's pseudo-IR films.)

 

[Ashfaque]

Thanks a lot for the explanation and reminding me about the handbook, Thomas. I found a B+W file ("BW_Filter_Tip_Infrared_filter_EN.pdf") that suggests that it is a 695 nm filter.

The B+W 092 infrared filter 695 is suitable for use as a universal IR filter and is preferred for use in pictorial photography. It displays a suitable IR effect with most digital cameras. At over 90%, the transmittance from 730 nm to 2000 nm is very high. That makes it possible to take shots of the pure red and IR range. In the latter case, it is possible to fully exploit the digital camera's residual IR sensitisation.

695 is also mentioned in the handbook, which I didn't bother to read properly.

Bests,
Ashfaque