EIR hints?

AutumnJazz said:

But the pictures on Flickr that were made with a yellow or orange filter seem to just be too yellow or have a yellow cast, whereas the ones done with a red filter look really interesting.

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Have you also noticed that most of these "interesting" looking pictures also use a Circular Polarizer filter, instead of just the Hoya 25A red? Maybe PE can comment on the effects of a polarizer on EIR, as the Orange filtered pictures do seem to confirm the 2 toned pictures PE describes, with an overall yellow / orange cast, although even these are combined with a CP.

Orange and yellow are similar, just shifting color temperature, but still produce 3 color images. Red filters produce 2 color images, and deep red produce one color images.

Polarizers may only reduce any UV that seeps through the yellow filter, particularly those that "leak" UV or in situations with lots of UV. That is all I can think of. They would also reduce the reflections from water increasing its apparent blackness. Water absorbs IR and should appear black, but reflections can cause light spots.

PE

Photo Engineer said:

EIR and Aerial Ektachrome are functionally identical. In fact, the sale of the "amateur" product or consumer product was probably driven by the sales to the military and to forensic labs. The roll films were therefore driven by the original military and forest service products used in aircraft.

As for speed, IDK. I have not used the military product for years.

PE

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Oh, by sensative I didn't mean speed. I meant to ask if EIR is/was sensative up into 900nm like HIE is/was.

IDK. You would have to compare the spectral sensitivities on an old Kodak data sheet. My personal opinion is "NO" it was not sensitive into the IR as far. That is based on purely technical arguments or assumptions that may be incorrect.

PE

From the technical data sheet: "SPECTRAL SENSITIVITY KODAK AEROCHROME III Infrared Film 1443 is sensitive to ultraviolet, visible, and infrared radiation to approximately 900 nm."

So, yes, its IR sensitivity is *about* the same as HIE. Reproducing the halation effects is a different matter.

See attached graphic with the two spectral sensitivity charts overlayed on each other.

Well then, I was wrong, sorry. But OTOH, see the dip in sensitivity at about 500 - 550 nm. This goes to my post in another thread on quality testing of IR films. This hole allowed dim greenish safelights to be used to examine the film under some conditions. I can verify this if anyone is interested, and probably come up with a sensitizing dye structure FWIW.

PE

Amuderick,

To be precise, from comparing those two spectral charts one can only directly conclude the proportionality in IR response of the two films.

The speed is different in both charts and related to two different aim densities. If I interpolate to neutral-density 1, and I’m not sure whether I just might do so, the HIE would be one stop more sensitive.

EDIT: it schould be `transpolate´ or something like that... I guess you'll get the point.

Polarizers

The effect of polarizers is dependent on wavelength.

It is said to dimish from dark red onwards. Which means that one could use crossed polarizers for IR-filtration. (Well, that would be dependent on the steepness of that loss in effect.)

AgX said:

Amuderick,

To be precise, from comparing those two spectral charts one can only directly conclude the proportionality in IR response of the two films.

The speed is different in both charts and related to two different aim densities. If I interpolate to neutral-density 1, and I’m not sure whether I just might do so, the HIE would be one stop more sensitive.

EDIT: it schould be `transpolate´ or something like that... I guess you'll get the point.

Click to expand...

I know people shoot and develop HIE in many different manners, but I've had best success rating both of these films at ISO200. It must be my HIE development strategy that slows it down? I find that it's too grainy at 400.

Tim

AgX said:

Polarizers

The effect of polarizers is dependent on wavelength.

It is said to dimish from dark red onwards. Which means that one could use crossed polarizers for IR-filtration. (Well, that would be dependent on the steepness of that loss in effect.)

Click to expand...

Polarizers do not shift color balance when used with color film. They are generally considered a "neutral density", but mask surface reflections which vibrate in a given plane. Circular polarizers are unique for digital cameras to assist in eliminating the effects of aliasing due to the linearly lined slits in a regular polarizer. Otherwise both types act alike in removing reflected light from images.

If a given polarizer has no absorption in the UV or IR, then it is ineffective in those regions, but we cannot see that visually. A spectrum would have to be obtained in order to exactly predict the effects on a given film. In fact though, polarizers have no UV absorption to speak of, and so it is normal to use a polarizer and a UV filter. IDK about the IR region.

PE

PE,

At this link you'll find a graphic showing the spectral effect of two polarizers crossed:
http://www.anchoroptics.com/catalog/product.cfm?id=285

Such a filter would yield the steepness needed for a photographic IR-filter, but in contrast to dye-IR-filters it would the same time allow to variate the transmission within the visible spectrum.

Photo Engineer said:

Polarizers do not shift color balance when used with color film. They are generally considered a "neutral density", but mask surface reflections which vibrate in a given plane. Circular polarizers are unique for digital cameras to assist in eliminating the effects of aliasing due to the linearly lined slits in a regular polarizer. Otherwise both types act alike in removing reflected light from images.

Click to expand...

I've been wrong about things before, but I thought circular polarisers predated digital cameras and the reason for their existence was not aliasing owing to linearly aligned slits, although maybe that's a help.

I was under the impression that a circular polarizer was necessary for any camera which used mirrors to bounce light around - i.e. pretty much any modern camera with TTL metering/autofocus which uses half-silvered mirrors. If you use a linear polarizer the angle of polarisation of the incoming light will alter how the light is reflected by the assorted mirrors (Brewster's angle and all that) and throw off the metering.



Anyway, ignoring that, an on-topic question; anyone know if EIR is suitable for astro-photography? The wife has a telescope which I've been meaning to hook the camera up to for a while and thought EIR might be interesting; I'm not sure how to attach a filter in that scenario though. And I presume if the fillm is blue-sensitive all over, there's probably still quite a lot of blue in the night sky. Hmm...

In case you could not use a filter in front of the lens you can try to install a film filter just in front of the film plane.

More explanation is needed here.

If you look at the spectrogram referenced by AgX, you will see transmission of a crossed polarizer out to 1000 nm. What is not clear is that to get this deep blocking of light, you need to cross two of them (of the exact same type). This blocks no deep red, it is blocking all visible light and allows deep IR. The filter is visibly neutral but virtually wide open in the IR. If you use one of them to control reflections, you get an overall blocking of reflected light and little blocking of UV or IR.

In fact, the filter has about than 50% transmission at 900 nm, which is IR. This is not red. In fact, you will only lose about 1/2 of the light at 900 nm and have complete transmission at 1000 nm. That is a lot of light. Actually, I used a cross polarizer to block visible light with a digital camera and take quite good IR photos with it. If you partially block the visible spectrum, you then can get an EIR type effect combining color and IR using digital.

So, a pair of polarizers can be set to achieve any density neutral density you wish when crossed but be open in the IR region, and a single one is the normal type used on cameras which just merely blocks out unwanted reflections.

With sincere apologies, since EIR is not available I have shot the following:

Left picture, crossed circular polarizers

Middle picture WR IR filter (deep red - #87)

The rightmost photo is the normal (digital) version.

Both shot with a Nikon D70 to illustrate this situation more clearly. It probably belongs on the hybrid forum and if so, demote me and banish the post.

BTW, the circularly polarized filter was not invented for the digital camera, but came into its biggest use there due to problems with linear polarization.

With apologies.

PE

Sorry, in case I was not clear concerning those polarizers. I only referred to them concerning any possible filtration to the effect a coloured filter would have, not to the effect of controlling polarized reflection (which is commonly linked to polarizers).

Two polarizers combined are known to yield a neutral filter of variable density by twisting them. This effect is what I referred to, with the exception that those filters are no longer neutral but yield a selective effect if applied to a spectrum including IR (in this case if the film is IR sensitive too.) By this gaining the effect a couloured (IR) filter would have, added by a variabilty of its opacity.
PE finally made this perfectly clear.



This all is true for polarizers we commonly have access too.
However, if you want to control reflection due to their degree of polarisation (the classical application of polarizers), there are special polarizers that control polarisation in the IR-range too. I doubt whether those have ever been applied to pictorial photography though.