General film sensitivity to IR?

[Athiril]

This is something that has been bothering me..

Silver blocks IR right? Shouldnt it then be absorbing the energy?

Is there a level of sensitivity to IR in film? And on colour film?


Got thinking on it, as my home made IR filter for my 12-24 (takes rear gels) gets me something like f/8 ISO1600 30sec in the middle of the day on my 30D - as the IR blocking filter is not removed.

Which got me thinking that it doesnt affect normal pics because of the difference in number of stops of exposure, which also got me thinking that blocking out enough visible light and increasing exposure would image IR on regular film?

 

[keithwms]

Silver blocks IR right? Shouldnt it then be absorbing the energy?

Bulk silver does block many wavelengths, but once you make grains of silver, the transmission is very dependent on particle size. Thin films of silver also have some surprising transmission ranges. Remember film grains are very thin and small and there are many spaces between, so you can certainly get some IR transmission through. Turns out that some very interesting evanescent transmission can happen between grains and at their edges, particularly with silver; this is the basis of subwavelength resolution microscopy with a near-field scanning optical microscope (NSOM), look up the papers by Thomas Ebbesen if you are interested. I will be pissed off of Thomas doesn't get the Nobel pretty soon.

Is there a level of sensitivity to IR in film? And on colour film?

Yes. Bear in mind the purpose of the antihalation layer found in most films. It prevents re-exposure by IR off the pressure plate of the camera. redder photons can go all the way through and bounce back and re-expose the film from the back, not a good thing usually.... unless you like glowy highlights a la HIE

Which got me thinking that it doesnt affect normal pics because of the difference in number of stops of exposure, which also got me thinking that blocking out enough visible light and increasing exposure would image IR on regular film?

Yes, and this is basically Robert Williams Wood's discovery, with UV and IR. He figured out that if you just block the visible light well enough, you can eventually get some 'invisible light' signal recorded. He invented the special blocking filters. But.... 'normal' films, even extended pan ones, have very low sensitivity past 800 nm... it takes special sensitizers to go up past that. Even with IR films like Rollei IR, superpan or the efke stuff, I am routinely looking at ~12 stop filter factors with a relatively low cutoff of the #87 filter!!!! Plus, with whatever meagre IR sensitivity you do have with 'normal' films, you'd very quickly run into massive reciprocity issues. So... the answer is "yes, but..."

 

[Athiril]

So ND's dont effect IR exposure right? They pass IR?

I could use my IR filter + ND to make sure.

Yep.. I think Acros or Astia might be a good bet to try or any other film with excellent reciprocity characteristics, or something high speed.

I do have some HIE and EIR in the fridge.. but I dont want to waste them

 

[keithwms]

NDs will block a good bit of IR as well, and by the way, NDs aren't really neutral, and they become less neutral outside the visible range. The results with IR will vary, you'd have to slap them in a spectrophotometer. Generally I do not think they are a good choice as a vis-blocking/IR-transmitting filter. If desperate, you can use unexposed but developed E6 film, that will work better.

You can eke quite a bit of IR sensitivity out of the pan films if you have the patience and a good filter. But they will really tank well before 800 nm. I am talking near IR. Nothing like HIE.

Try rollei superpan. Marvelous stuff. Colour IR, well, you could do colour sep using the superpan. MY EIR, frozen as it was, seems to have died

 

[Athiril]

Yeah I did the E6 thing with my Sigma 12-24mm for a rear gel, as i couldnt find any IR gels to buy, 1 layer wasnt enough, 3 too much, 2 worked exceptionally well for colour.

I've got an IR filter but hold it up to my eye outdoors and I get redscale after my eye adjusts... though I think it should be fine, have heard of that IR goggles made with colour gels thing

I got 2 rolls of EIR, from Sweden stored in a draw in their cold temp over there, used one roll, but seemed to overdo the first dev step, so very thin, saving the last.

You can get EIR fresh on Ebay in 120, expensive though.

 

[Athiril]

Just made some exposures on Shanghai GP3, an compensating for reciprocity like its FP4 (since I've seen that comparison in regards both to reciprocity and look online), most at EI200, one at EI100.

Time was f/5.6, 1 minute compensated (up from 16 seconds) for EI200, 3 min for EI100.

Calculated it from testing the filter on my 30D @ ISO3200, f/1.4, 1/30th.

Am somewhat hoping the difference in number of stops in sensitivity is around the same. We'll see.

Edit: Okay just finished fixing and washing with photoflo, all exposures look spot on, I dont know how IR my IR filter is, I'll play around with the colour shot I took on my dSLR with it to determine that.

Old IR I did using my home made IR filter:

IR with the bought filter, daylight-balance:

Some digital balancing:

Would be interesting to see it on the 4 layer fuji film.

 

[Athiril]

There were 13 stops of difference between the exposure I used for shots without filter, and with, my EI200 non-filter shots are a tad dense (According to the scanner histogram) so a little over-development, but nothing too bad, and my EI200 IR shots are a bit denser than the non-IR shots, so I would estimate the difference at 12 stops.

Non-IR

IR

Another IR

Cant decide if these are IR results or not, I need different subjects, another test, a b&w conversion from the digital doesnt look different fro the results.. perhaps try some colour film.

 

[cmo]

For analog IR photography you really need an IR film. There are a few black-and-white traffic surveillance films (Agfa, llford, relabeled Agfa/Rollei, Kodak Hawkeye) with a little IR sensitivity (up to 750nM) and little IR effect and only one real IR film named Efke IR 820 (820nM) with a strong IR effect. For color film, EIR is the only choice at this time. If you have good results with color films and dense filters show us more and explain how to do it, many will be interested.

 

[Athiril]

For analog IR photography you really need an IR film. There are a few black-and-white traffic surveillance films (Agfa, llford, relabeled Agfa/Rollei, Kodak Hawkeye) with a little IR sensitivity (up to 750nM) and little IR effect and only one real IR film named Efke IR 820 (820nM) with a strong IR effect. For color film, EIR is the only choice at this time. If you have good results with color films and dense filters show us more and explain how to do it, many will be interested.

I have HIE and EIR in the fridge.

I'll do a roll of colour to test and post the results

 

[keithwms]

Athiril those shots in post 7 don't look IR to me at all. Actually, quite the opposite: it looks more like the kind of thing I see with UV photographs- lots of scattered light softening the shadows and lots of haze scattering. Interesting though. Keep up the experiments! Maybe you'll get somethig even more interesting.

RE: colour IR, I think it is a bit of an artistic risk right now, unless you are really good with it. People are taking plain-jane colour photographs and diddling the hue slider in photoshop and presto, all kinds of wacky effects, and it's become a bit of a fad. However I have seen some EIR work that appealed to me greatly. As I recall, it involved only models clad in red. The red is fiercely intense, the models' skin rather porcelain. If I were doing colour IR I'd go straight for that approach and avoid scenes in which the other 'normal' colours play a big role... to my eye the false colours just clash too much with the conventional primaries.

 

[Jerevan]

There is an older thread, which may prove informative, although slightly off-tangent:

(there was a url link here which no longer exists)

 

[Athiril]

keith:

I wasnt convinced about them being part of the IR spectrum, but it looks pretty much the same as when I take the digital colour IR and do a colour b&w conversion, so to me its kinda in-conclusive.

But if the filter let through simply that much visible spectrum, then that would be evident in the digital shot, given that the separation difference between with and without on my digital (due to internal IR blocking filter) is 13-14 stops, and the film is less - 12 or even 11 stops, then one logically concludes if the filter lets through that much visible spectrum at +12 stops it should be more evident in the digital shot and begin to over-expose via visible spectrum on the digital..

Interesting you mention that it could be UV.. Im sure the 30D is less sensitive to it than IR.. definately have to give colour film a go when its daylight again.

There is an older thread, which may prove informative, although slightly off-tangent:

(there was a url link here which no longer exists)

Thanks, will have to look up the various spectral sensitivity for the colour films I have to start with the most sensitive (apart from EIR )

 

[AgX]

Silver blocks IR right? Shouldnt it then be absorbing the energy?

Is there a level of sensitivity to IR in film? And on colour film?

You are mixing up metallic silver and silver halide.

Silver halide is transparent to IR.
Metallic silver is opaque to IR from a certain compactness on (silver filaments versus thick homogeneous silver.

 

[Athiril]

Also found some info on direct sunlight in general.

"Bright sunlight provides an irradiance of about 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared light, 445 watts is visible light, and 32 watts is ultraviolet light."

 

[Maris]

By experiment I have found that the exposure for Tmax 100 behind an IR720 filter (cheap Chinese variety) is 8 minutes at f5,6 for a regular bright sunny day scene.

The resultant positive looks similar to what I get with Tmax 100 behind a familiar #25 red filter.

Conclusion: Tmax 100 is not sensitive to the oodles of infra-red the IR720 filter lets through. Tmax 100 is sensitive to the tiny amount of red that leaks through the IR720 filter away from its main transmission band.

 

[Kirk Keyes]

Conclusion: Tmax 100 is not sensitive to the oodles of infra-red the IR720 filter lets through. Tmax 100 is sensitive to the tiny amount of red that leaks through the IR720 filter away from its main transmission band.

That is an excellent conclusion!

It's not a way to get IR, just a way to get really long visible light exposures.

 

[Photo Engineer]

Remember that color IR is false color with the dyes shifted in the visible and IR spectrum. And so if you try to use color with IR illumination, you do not get what you would with real color IR film. The explanation is long and tedious and has been posted here at least twice AFAIK, so I am not going to repeat it. Basically though you get a Green, Red and IR exposure, but no blue exposure, thus the reason for the red filter or orange filter.

PE

 

[Athiril]

Cheers, I'm about to give it a go, starting a +12 stops on box speed with reciprocity compensation and bracket around that, to see if I get anything useful or interesting for landscapes.

 

[Darkroom317]

What about Tech Pan and infrared?

 

[2F/2F]

Remember that color IR is false color with the dyes shifted in the visible and IR spectrum. And so if you try to use color with IR illumination, you do not get what you would with real color IR film. The explanation is long and tedious and has been posted here at least twice AFAIK, so I am not going to repeat it. Basically though you get a Green, Red and IR exposure, but no blue exposure, thus the reason for the red filter or orange filter.

PE

The EIR data sheet explains it beautifully and briefly, and even has a picture, so you can just direct people to that.