What is the "AURA" effect with IR film?

[sanking]

I bought some 4X5 Rollei 400 IR film from Freestyle Sales. On the package there are instructions for development, and a note, "AURA" effect by overexposing.

Sadly, I never heard of the AURA effect. Can someone explain what it is?

Sandy King

[Vaughn]

My guess (and only judging from Kodak's B&W IR film), is that the lack of an anti-halation layer allows for some light in the brightest areas to pass thru the film and then expose it again as the light reflects off of the pressure plate (or film holder on LF cameras) of the camera. Hence the "arua" around the highlights. This why 35mm cameras with patterns on the pressure plate did not work all that well with IR film...the light would bounce off the pressure plate unevenly.

I noticed the same effect with x-ray film in LF cameras(again. no anti-halation layer).

Vaughn

[Brian C. Miller]

Vaughn is correct, the "aura" effect comes from the lack of an anti-halation layer. I never saw the patterns from the pressure plate myself, though.

The halation is most significant on 35mm size film. You will not (of course) get the same area of halation using larger formats. It will look minimal on 120, and almost nonexistant on 4x5. The most halo-ed film was Kodak HIE, RIP.

The minimum filter for this product is Red 29 (B+W 091). I use B+W 092, and Hoya 720 has the same effect. Past that, the film really isn't especially sensitive, and the exposure must be significantly increased. Bracket at ISO 50, and go from there.

[Vaughn]

Vaughn is correct, the "aura" effect comes from the lack of an anti-halation layer. I never saw the patterns from the pressure plate myself, though.

The halation is most significant on 35mm size film. You will not (of course) get the same area of halation using larger formats. It will look minimal on 120, and almost nonexistant on 4x5. The most halo-ed film was Kodak HIE, RIP.

The pressure plate info came from a fellow here at the university who found he had to tape a smooth piece of paper over his pressure plate to avoid the pattern. I have not used IR in 35mm myself.

Is the halation differences in format sizes just due to the enlargement factor? I got some pretty substantial halation on 7x17 using x-ray film.

Vaughn

[Peter Gomena]

Try putting a piece of white paper behind the film. You'll get plenty of aura then!

Peter Gomena

[sanking]

The minimum filter for this product is Red 29 (B+W 091). I use B+W 092, and Hoya 720 has the same effect. Past that, the film really isn't especially sensitive, and the exposure must be significantly increased. Bracket at ISO 50, and go from there.

First, thanks to all for the responses about AURA. That certainly makes sense.

So the film is ASA 400 but only for exposure to visual light? For full IR look you have to use a 92 or 720 filter and increase exposure? I have found this to be aboutr +5 stops for the Ilford SFX. Would that be about right for the Rollei 400 IR with a 92 or 720 filter?

Sandy

[Jim Edmond]

I've just run a roll of IR400 (35mm) with a Hoya R72. 5 stops compensation seems to be correct.

[Brian C. Miller]

Is the halation differences in format sizes just due to the enlargement factor? I got some pretty substantial halation on 7x17 using x-ray film.

YMMV, caveat emptor, everybody uses the stuff differently. Yes, the halo remains the same, but the enlargement is what makes the difference. Of course, a film with an anti-halation layer, like Konica or Ilford SFX or whatever, will have about half the halo. It is also quite easy to expose the film and get good results without exposing for the halo. I have heard other people talk about getting a pressure plate pattern, but I always shot HIE without the sun in the frame, and I didn't expose for radical halation.

So the film is ASA 400 but only for exposure to visual light? For full IR look you have to use a 92 or 720 filter and increase exposure? I have found this to be aboutr +5 stops for the Ilford SFX. Would that be about right for the Rollei 400 IR with a 92 or 720 filter?

Yes, Kodak HIE was the only film that was equally sensitive throughout its entire range. EI 12 sounds about right. However, I can't see or meter in IR so exposure is tricky. One time I was completely in the shade among evergreens, and what I didn't know is that the area was chock full of IR light. The N frame was actually N+1, and my N+2 shots and above were nearly bulletproof. The evergreens looked awesome, though, as good as a deciduous canopy.

One of the things that I really like about HIE is its extended IR sensitivity, so that all the vegetation reflects IR, not just deciduous-type plants. (I don't miss it yet because I have a freezer full) The best images for IR films will come from grass and deciduous trees. Evergreens will range from grey to black, depending on the species. You will have to experiment.

What will be reliable is that everything will look crystaline clear. No haze! I have a photo of a mountain (Mt. Hozomeen) from over 25 miles away, and it is absolutely clear.

[rguinter]

Sandy:

These on HSI 4x5-inch.

I don't know if the blooming effect is significant with 4x5-inch but I sense it is (somewhat) in the highlights.

Your opinion is welcome.

Bob G.

[rguinter]

...The minimum filter for this product is Red 29 (B+W 091). I use B+W 092, and Hoya 720 has the same effect. Past that, the film really isn't especially sensitive, and the exposure must be significantly increased. Bracket at ISO 50, and go from there.

I have quite a bit of this in 120-size that was custom cut from the equivalent Aerochrome.

I shoot it in my Fuji 645 with a red-grad over a Y2 and the effect is quite nice shooting at ASA 50.

See my photo 4, post # 7 in this thread:

http://www.largeformatphotography.in...ad.php?t=68794

Bob G.