Infrared Filters: I'm Stumped

[nation_of_pomation]

Hi all,

I've been toying with the idea of shooting IR film and have some laying around (a roll of Kodak HIE I inherited, some Ilford SFX [I know it isn't real IR], and one or two other generic IR films intended for traffic cameras), and so I grabbed up 2 generic IR720 filters off eBay without thinking about it. I'm closer to having an excuse to try shooting some IR, but now I've got a couple of questions I can't seem to Google a straight answer to.

1. Why can I see through the IR720 filter I have in 52mm, but not the one in 40.5mm? I thought they should have the same opacity, but they don't.
2. Was IR720 the right way to go, or should I have picked higher wavelengths?
3. How can I know if my lenses have a hotspot?
4. Also, what is a hotspot, really? I had never heard of the term until I was dearching for answers a few minutes ago.
5. Do IR films all have the same ISO sensitivity or no? Is there a chart or something that would explain it?

Any and all suggestions would be great! IR is a very cool but very intimidating-seeming type of photography, but I really want to try it.

 

[Chris101]

Hiya Nat!

1. no idea. Thickness, coating or maybe just different filter. You said they are no-name filters. I have found that, if I look at a lightbulb, I can just see it dimly through a Wratten 89B, which is my usual filter of choice. A 93 is more IR-like, but the exposure factor is much greater.

2. See above. The IR720 is probably close to an 89b. Without a careful analysis of the transmission curve of each filter you won't know for sure. Just shoot with them and hope for success.

3. look at the pictures. The whole concept of lens hotspots was little known esoterica until digital IR.

4. it's a small, circular shaped bright spot in the center of the image. The high reflectivity of a digital sensor reflecting off the glass of the lens is thought to be the cause. You likely won't see it with film.

5. no. The sensitivity of IR film is based on infrared light, and we can't see that. I shoot SFX at box speed, or pushed one stop. I shoot HIE at iso 500, and then develop it just the same as I do for trix pushed one stop. I live in Arizona, where IR abounds. If it's not so bright where you live (and I think the East coast is not as bright as it is here, then give the film more exposure. It's very much a trial and error thing. Since supplies of IR film are dwindling, bracket like crazy.

 

[Bob Michaels]

I shot a lot of HIE years ago, both 35mm and loved it in 120. I decided a standard red 25A worked best for me. A stronger filter with give you darker skies and lighter foliage but that was all and it got old quickly.

I used different iso's, bracketed and kept notes. I learned that my best exposures were always f8 @ 1/250th. (that was with 25A). Finally I quit being misled by the exposure meter and always shot f8 @ 1/250th. Remember different light meters react differently to the IR part of the spectrum even though they are consistent in the visible portion. So ignore everything having to do with iso and a meter and just find the exposure that works best for your taste, your film and your exposure. Then use the same exposure all the time, tweaking it for subject luminance as needed. Also remember there is no "right" or "wrong" exposure with IR film. You get different looks with different negative densities so you have to find what gives the look you want in your prints.

BTW, you do have to remove HIE from the canister and load into the camera in the dark as Kodak says. Because it has no anti halation layer, the light will travel down the leader tongue into the canister and fog some of the first frames on the roll.

I know nothing about SFX for "generic IR" film. You are on your own there.

 

[nation_of_pomation]

Thanks guys! The generic IR film "for traffic cameras" says it's DIN 27, so I guess I should start like it's ISO 400 and bracket based on that?

 

[Doug Smith]

Like Bob, I've gotten best results with HIE exposing at 1/125th a second at f/11 and using a B&W 092 filter on sunny days. I just have a couple rolls left and will be sad to see it go.

 

[sevo]

Thanks guys! The generic IR film "for traffic cameras" says it's DIN 27, so I guess I should start like it's ISO 400 and bracket based on that?

With IR filters, metering TTL? Sometimes, yes - these "traffic films" have a pretty high nearest IR sensitivity, as their intended purpose is to photograph fast moving cars with a non-blinding deep-red flash. This relative linearity from visible red to nearest infrared implies that TTL through the meter is often close to the mark at nominal speed and without applying correction factors. All that provided that your camera does not have a IR filtered meter sensor - quite a few AF age cameras do...

Metering with a hand-held meter you'd better start off with at least three stops of filter factor to start with, and bracket by several stops from that. Even after you found a working factor, you'll still have to bracket in any case, as the relationship between visible and infrared light is highly variable, depending on invisible factors like the humidity throughout all layers of the atmosphere.

 

[Bob Michaels]

Thanks guys! The generic IR film "for traffic cameras" says it's DIN 27, so I guess I should start like it's ISO 400 and bracket based on that?

Nope, DIN is just like ISO. It is a number your plug into your light meter to take a reading to determine exposure. Same problem exists, the light meter measures visible light and you are exposing your film mostly with light from the IR part of the spectrum.

I know it is counter intuitive to many of you not to start with a light meter to determine exposure. After all, that it the way you do it with film that registers visible light, right? But if you start with a fixed exposure than proceed using that as a base line, you will reach the point of making consistent exposures the way you want them quicker.

 

[ZeissFan]

There are several filters that you can use with Kodak HIE film:

1) Deep red filter, which is commonly available.

2) A very deep red filter, which filters nearly all light. You can see through it, but just barely.

3) A true infrared filter, which blocks all light rays except for infrared. You cannot see through this filter.

With Nos. 2 and 3, these are of limited use on an SLR, because the view is impeded. Here is another case when a rangefinder will work much better.

Also, you should not use Kodak HIE with any autowind camera that uses an LED in the film chamber to position the film. The LED can/will fog Kodak HIE film.

With the newer Rollei-branded infrared film, you want the No. 2 filter mentioned above -- the one that is very deep red and you can barely see through.

With the Rollei-branded film, don't use the visually opaque filter. You'll just get a blank roll. And the normal deep red filter doesn't filter enough of the spectrum to be useful.

The Kodak film should be loaded (and unloaded) in complete darkness. I always do the same with the Rollei film. I think the spec sheet is a bit vague on this. Better safe than sorry.

With the Ilford SFX film, the normal deep red filter is the one to use. It won't give you true infrared effects, because it isn't a true infrared film. I think it was described as producing photos with infrared-like qualities or something along those lines.

 

[ZeissFan]

Kodak HIE with a regular deep red filter:

Nikon F2A, taken in the mid-1980s in the spring. Anything with chlorophyll turns white.

The Rollei film with the nearly opaque, very deep red filter:

Contax IIa with 21mm Biogon.

 

[Roger Hicks]

HIE has a 'green gap', ie. very little sensitization to green light: just blue (residual halide) and red/IR (dye sensitized). You therefore get strong IR effects even with deep yellow filters. All more modern films are green sensitive and therefore require a very deep red filter: T50 695nm or even T50 715nm is ideal (T50 = 50% transmission at the stated wavelength, 695 or 715 nanometres).

Cheers,

R.