Acros Reciprocity

RattyMouse · Aug 20, 2017

What is it about Neopan Acros that gives it such amazing reciprocity characteristics? The photochemical agents are the same in all films so what does Fuji add to make it so good for long exposures?

Prest_400 · Aug 20, 2017

That's a good question. Also, how Fuji has Provia and had Astia and T64 which all were IIRC excellent in reciprocity. Overall also E6 and Acros seems better suited for long exposures than Color Neg.

Maybe the Orthopan spectral response helps in that matter.

If PE chimes in it would be interesting to know about reciprocity.

Photo Engineer · Aug 20, 2017

Reciprocity, raw stock keeping and latent image keeping are all controlled by a family of preservatives including heavy metal complexes and organic chemicals. Each company has a proprietary mix of these. Kodak uses Osmium and Iridium in emulsions at levels of a few milligrams / mole of silver. That is a very tiny amount. They also use phenyl mercapto tetrazole and tetra aza indene. There is some information in the various textbooks on this.

Method of preparation of the raw metal salt and the addition method are both critical in getting them to work.

PE

laser · Aug 20, 2017

Ron is correct. I think the first still camera film to demonstrate the extraordinary reciprocity with heavy metal doping was T-Max (mid 1980's) followed by EKTACHROME 64T (1988) . At long times TMX-100 is faster than TXP320. Ektachrome 64T had the same speed and color balance from 1/10th to 100 seconds exposure. Somewhere I have the demo transparencies that we used to announce the film in the 1988. Similar techniques have been used by Kodak and Fuji in every professional film since.

Added comment: the technology used in Kodak and Fuji films are similar. The film differences are the choices made in the film design and the manufacturing process.

Rudeofus · Aug 20, 2017

I think there are two physical effects which control reciprocity:

how many photons does it need to create a stable silver nucleus?
how quick is the decay of unstable silver nuclei?

The first is addressed by sensitizers, of which Acros seems to use a very modern one, just like all the other advanced emulsions from Kodak and Ilford. The second effect seems to be governed by the preservatives mentioned by Ron. Clearly, Fuji seems to have found something spectacularly good here, because no Kodak or Ilford Emulsion offers reciprocity up to two minutes AFAIK.

Photo Engineer · Aug 20, 2017

Check Bob's answer above Rudi. Kodak has data out to at least 100 seconds. That is close to 2 minutes and it was good. So, if they checked out to 2 minutes.....?

IDK, but this is close enough to me.

PE

Rudeofus · Aug 20, 2017

Ron, if I look at the TMAX 100 data sheet, it says "+1/2 stop at 10s, and +1 stop at 100s", which sounds very different to Fuji's "No exposure compensation is required for exposures at shutter speeds of less than 120 seconds.". Don't get me wrong, TMAX beats older emulsions, even Tri-X hands down, but Neopan Acros is definitely ahead here.

IanBarber · Aug 20, 2017

As Acros sheet film is coming out of production it would be a niche market for Ilford or Kodak to produce something which matches the reciprocity of Acros.

Kevin Caulfield · Aug 20, 2017

So glad I had two rolls of Acros with me for a beautiful sunrise in Robin Hood's Bay two days ago. Not only that but I also had a roll of Neopan 400 with me. Stand by for photos.

RattyMouse · Aug 21, 2017

IanBarber said:
As Acros sheet film is coming out of production it would be a niche market for Ilford or Kodak to produce something which matches the reciprocity of Acros.

That's my concern exactly. I am certain that Acros will be gone in 5 years or less and it would be good if an Ilford film could replace it in this area.

Ian Grant · Aug 21, 2017

Photo Engineer said:
Reciprocity, raw stock keeping and latent image keeping are all controlled by a family of preservatives including heavy metal complexes and organic chemicals. Each company has a proprietary mix of these. Kodak uses Osmium and Iridium in emulsions at levels of a few milligrams / mole of silver. That is a very tiny amount. They also use phenyl mercapto tetrazole and tetra aza indene. There is some information in the various textbooks on this.

Method of preparation of the raw metal salt and the addition method are both critical in getting them to work.

PE

I think you mentioned in the past that Acros probably uses a different gelatin to their other emulsions. The Acros emulsion is particularly prone to issues in Rodinal unless care is taken due to the free Hydroxide it contains. Plenty of reports (& images) of reticulation and emulsion lifting/flaking of the base.

Pre the merger between Agfa and Gevaert (1964) there was no "free Hydroxide" in Rodinal, but it was reformulated after the merger to bring manufacturing costs down. This coincides with the major improvements in film hardening at Agfa-Gevaert and Ilford. FP3 & HP3 had quite soft emulsions, the new emulsions FP4 & HP4 were extremely well hardened.

Fuji use whale gelatin in some emulsions, as whaling is technically banned no photographic company (outside Japan) has used it. Japan allows whaling for "Research" but there won't be large quantities of whale gelatin available. Choice of Gelatin will have an effect on sensitivity and reciprocity as well as the other factors you mentioned.

Ian

lantau · Aug 21, 2017

I'm still a beginner, having developed my first film in autumn 2015. And I haven't used much Acros, nevertheless it is a favourite film of mine. I have developed 3x135 and one 120 roll in Rodinal. And a few in D76. I didn't notice any difference.

Photo Engineer · Aug 21, 2017

Fuji was experimenting with polymers as replacements for all or part of their gelatin. In fact, there are indications that they used it in their color films in the form of polymeric couplers. They have also experimented with fish gelatin.

PE

RattyMouse · Aug 21, 2017

Rudeofus said:
Ron, if I look at the TMAX 100 data sheet, it says "+1/2 stop at 10s, and +1 stop at 100s", which sounds very different to Fuji's "No exposure compensation is required for exposures at shutter speeds of less than 120 seconds.". Don't get me wrong, TMAX beats older emulsions, even Tri-X hands down, but Neopan Acros is definitely ahead here.

Yes, Acros is definitely ahead of Kodak in this property and it will be a shame to lose this film once it goes.

Photo Engineer · Aug 21, 2017

Well, IDK what was sacrificed (or not) in Fuji's gain. This is a problem of pushing on a water balloon. I really don't know.

PE

Acros Reciprocity

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