Some questions about IR contamination

[Deanan]

Wow! That's a lot of IR contamination. Good example.

One thing that's not talked about much is that fabrics (or anything for that matter) can act very much like ND filters do. A black fabric can absorb alot of the visible spectrum and reflect a ton of IR/Far-Red. In that shot, the black fabric becomes a very large IR/Far-Red bounce card.

Things can also get interesting if the fabric has a weave to it. If the light source is causing the fabric to cast a shadow on itself (at the weave level) you can get a higher contrast response from the weave that you'd normally see. (ie. part of the weave will be in shadow from the light, and part will be reflecting alot of IR).

 

[Pawel Achtel]

One thing that's not talked about much is that fabrics (or anything for that matter) can act very much like ND filters do. A black fabric can absorb alot of the visible spectrum and reflect a ton of IR/Far-Red. In that shot, the black fabric becomes a very large IR/Far-Red bounce card.

Things can also get interesting if the fabric has a weave to it. If the light source is causing the fabric to cast a shadow on itself (at the weave level) you can get a higher contrast response from the weave that you'd normally see. (ie. part of the weave will be in shadow from the light, and part will be reflecting alot of IR).

Ideed. I ended up with massive IR contamination when shooting time lapse with Canon EOS 40D, B+W ND3.0 on the beach on a hot day. Interesting effect, but impossible to correct in post. The sand turned dark brown basically. Also green leaves and grass tend to do that.

 

[Ken Robings]

When I worked at Schneider Optics, B + W (owned by Schneider) had a IR/UV cut filter called a 486. It "completely" cuts out IR and UV by coating the filter with something like 27 coats, creating a cliff at either edge of visible light. A typical (and less expensive) UV/IR filter will have a gradual slope to/from visible light. The 486 does away with the slope by the numerous coatings.
It was designed for the goverment to increase performance of CCD's, now available everyone (if they still make it, it's not cheap)

 

[Rob Castiglione]

Yes, B + W still make the 486. I use it on my Nikon lenses with ND screw on filters .9 and upwards. It works very well though it cant be used on wide angle lenses.