View Full Version : Infrared Light Source and Film

Michael Kadillak
16-Dec-2005, 22:46
After reading a similar post over at APUG, I began thinking about darkroom work with night vision equipment.

I have been using an infrared monocle for some time in the darkroom and while I was assisting someone in the darkroom get acclimated to it recently, I noticed that there is a small green glow of light about the rear eye piece. On the same subject, my infrared light source on the monocle emits a small red glow as it produces the infrared light. A wall mounted infrared light LED emits the same red glow as well.

I believe that the green stray light from the eyepiece could fog film so I feel that I need to contain this stray light from reaching the film. That is easy enough to do. My question is concerning the red infrared light. Could it also fog film or am I concerned about nothing.

Any physicists out there? I guess I could do some tests but I have been rather busy lately and wanted to try the easier route.

Thanks in advance.

16-Dec-2005, 23:49
Good grief, what does something like this cost?

John Berry ( Roadkill )
17-Dec-2005, 01:47
I have been 6-8 " away from negs as I inspect during DBI for as long as 15 sec, more than once in the same spot during development. Fp-4 in pyrocat. No negative effects. My unit has an LED source on it so it's that close also. I have had no fog from loading film from the green. I keep the reticle right up next to my eye. I would not recommend using glasses with them as it might have the unit out far enough to cause a problem. Just a guess but I would think it might be below threshold anyway. There is no need for glasses as you focus unit anyway. Have you had any thing in your process that gives rise to this concern? Somthing for me to look out for?

Michael Kadillak
17-Dec-2005, 06:52
The cost has dropped to several hundred dollars per unit, but the benefits are many particularly during development by inspection (DBI).

I have not encountered any specific adverse effects John with using these devices, but the engineer in me seems to want to make damn sure that the base fog does not kick up even slightly. I realize that even a low wattage green safelight could have the same effect with the conventional methodology. Assumning a conclusion has its risks and with the cost of ULF film I just want to eliminate any operating variable to the degree possible.

Guess I will run a few sheets of 4x5 with and without and do some density measurements.

The next alternative I will try is to leave the battery power off of the light gatherer and the IR source completely and use an external panel IR source. The monocle works just fine with this external source of IR.


Ralph Barker
17-Dec-2005, 08:16
I don't use one, Michael, but it sounds like the on-board IR source is also emitting some near-IR visible-spectrum light. As such, wouldn't the potential effect of that depend on the film's sensitivity curve? That is, films with extended red sensitivity might show some fogging effect, while other films probably wouldn't.

You might tape a small section of an IR filter gel over the on-board source to reduce that risk.

Leakage from the green glow of the internal display, however, would make me nervous, too, particularly at the distances involved with DBI. Gaffer's tape might work for that, but watch out for your eyebrows. ;-)

Michael Gudzinowicz
17-Dec-2005, 08:33
You might try filtering the IR sources to remove the visible red component. By selecting longer wavelengths outside of the film's spectral sensitivity, brighter illumination with no risk of fogging may be possible. An IR filter or black exposed and developed Ektachome film may be used for a test to see if the night vision unit responds to the attenuated source. If you want to use film for a test, give it a very small pre-exposure to zone 0 or 0.5 to sensitize it without adding significant fogging that could mask a small amount of fogging from the IR source.

Linas Kudzma
17-Dec-2005, 08:54

I have exposed a half open film holder with containing FP4 to the IR light of my nightvison scope for 30 seconds from 1 foot away (I forget the model, but it's likely the one you have - got it from the Ebay seller). No fog whatsoever after development. Most films seem very insensitive to the wavelengths from this IR LED. I also worry about the green from the backside and am careful to keep it covered. Also, I'd be careful about looking into the IR light with my eyes. It's likely very powerful and IR can damage eyesight without us realizing it.