PSA: Dark Bags/Changing Tents may not be IR safe!

[MCB18]

Hello guys!

I just figured I would make this post here, because it might actually save some people quite a bit of grief. While this piece of information may not be news to some people, it was sure news to me!

This was a discovery made while someone was testing Hi-Con IR, because they were loading their sheets in a dark bag, which takes a while. They were having issues where the film would become fogged, they thought it might’ve been their fixer but the fixer was good, they thought it might’ve been the developer, but the developer was still good.

Someone suggested that the dark bag they were using might not be IR safe, so they went into another room where there was no windows, and they made the room as dark as they could. They still used the changing bag as they couldn’t fully light proof the room, but that suddenly fixed the problem anyway.

It has occurred to me that some of the issues that I might have been having with other infrared films, such as severe base fog on 1443 and 2424 on the same rolls as others were having no issues, may have been because I was using a changing bag in a room with a bunch of windows.

I will make another roll of 120 2424 after it defrosts to test this, and let you guys know how that goes. But, I suspect that this may be the issue.

If anyone else here can confirm that this is indeed a thing that happens, and share your experience, I would be very appreciative.

 

[BobUK]

I have read that some cameras with bellows can also fog infra red film through the cloth.

 

[xkaes]

I would assume that a changing bag or a camera bellows would be transparent to IR light unless specifically manufactured not to be. Even a dark slide would be suspect -- unless it were metal. Remember, IR light passes right through the "felt light guard" on 35mm cassettes!

 

[MCB18]

I can’t comment on all camera bellows, obviously, but I can say that the RB67 does use IR opaque bellows.

Speed graphic/crown graphics are also good according to folks I talk to.

Also from friends, a lot of newer view cameras use E-Tone bellows, which seem to also be IR opaque.

 

[Emily Cook]

I haven’t used it for a lot of IR yet but I’ve put a few sheets through my Chamonix 45H-1 as well without any noticeable IR fog

 

[lamerko]

You can test it easily. You need an IR source in the desired range and a digital camera/phone without a strong sensor filter. As a source, there are inexpensive 720 nm IR LEDs, as well as slightly more expensive 940 nm ones. You can also get flashlights directly - 850 nm models are common, but there are also more expensive 940 nm versions. For this purpose, they do not need to be particularly powerful.
Keep in mind that some materials that appear black and opaque to visible light can 'light up' in the IR range - they may actually become transparent. If the black changing bag is made from fabric with nylon fibers, there is a good chance that it provides little or no protection in the IR spectrum.