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  #1  
Old 7th September 2020, 01:34 PM
Terry S Terry S is offline
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Default Latent image - info anyone?

I've read a bit and pondered about this for a while now, but still have some unanswered questions.

Mainly, what length of time, will an image remain 'latent', on both photographic film and photographic paper?

It's often said that slower film emulsions should be developed asap after exposure. What would happen if one didn't? Would the image slowing disappear and one could reuse the film again, but this time develop it a bit quicker?

If we compare slow film to photographic paper, with the film having an ISO of 50 for example, and which has latent image fading, then how long can one leave an exposed sheet of paper, which must have a much lower ISO and i.e. presumably it's latent image fades much quicker than film. How long before the paper too loses it's latent image, or will there always be an image there, although much fainter?

As I'm going into the darkroom this afternoon, I think I'll make a couple of test strips on some different papers and then develop them over a week say, and see what difference, if any, time makes.

But in the mean time, is anyone more knowledgeable out there that can chip in with experience of a slow film not being developed soon enough, as an example?

And also, how come we are advised to develop asap, after exposure of a film, yet people often pop up saying that they've just developed, successfully, a film that has been at the back of a draw for 30 - 40 years. This goes totally against what advise we are given by film manufacturers.

Terry S

Last edited by Terry S; 7th September 2020 at 01:38 PM.
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  #2  
Old 7th September 2020, 02:41 PM
Richard Gould Richard Gould is offline
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I don't know much about the latent image, but I think it rather depend's on the film, certainly with Pan F+ if you don't develop within a very few days then the latent image will go, I speak from experience here, I used some for a special project a few years ago,and left the development for a couple of weeks until the project was completed, and only the last 2 had an image on them, all the rest had gone,checked my cameras and nothing wrong, so googled the problem and it seems that it is a feature of this film, develop it straight away or risk losing it all.
Richard
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Old 7th September 2020, 03:10 PM
Mike O'Pray Mike O'Pray is offline
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Terry, I wish you luck with anything resembling a definitive and know to be scientifically correct answer.

The only admission of a problem I have ever seen was that delivered to Photrio several years ago when Simon Galley of Ilford admitted in relatively vague terms that there was a latent image problem with PanF+

At that point he seemed to run out of facts. Is there a period in which Ilford guarantees no issue and if so how long- a week, 2 weeks, a month? Beyond that apparently impossible-to-pin down period what is the period when Ilford can say with a deal of certainty if not absolute certainty that some latent image fade will be present and finally if there a period beyond which Ilford can be certain that there will definitely be image fade and if so what is this?

If the latent image fade is a characteristic of slow films in general then I have never been conscious of such information from the makers nor have I seen threads on the subject other than that pertaining to Pan F+

Even with Pan F+ there always appears someone whose experience of exposing Pan F+ and then leaving it in a drawer for months and months is contrary to the announcement by Ilford.

As far as paper is concerned your experiment can at least be accomplished more quickly and there, at least in the context of pre-flashing, there would seem to be definite evidence of fade in perhaps as short a period as only days.

As pre-flashing tends to be a solution to be used when a print calls for this so is done instantly and the paper then exposed to the negative projection it is not normally subject to long delays

However it might be important should you need to work out how far in advance you can pre-flash paper negs so you don't do more than you will use in X days

Good luck with your experiment

Mike
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Old 7th September 2020, 03:13 PM
JOReynolds JOReynolds is offline
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Default latent image regression

Latent image regression (fading) occurs exponentially from the moment of exposure, fastest in fast (ultra-sensitive) emulsions. It is most noticeable in colour emulsions - the human eye is most sensitive to colour changes.
I was made aware of this in the 1970s when a professional lab was making runs of identical publicity prints on Agfa paper and blamed my equipment for inconsistent results - the first exposures were wound onto the core, so the last to be exposed were on the outside of the roll and therefore first to be processed. The images on each of the three colour-sensitive layers faded at different rates. At first the laboratory manager blamed the temperature control system in the processor (and ignored the paper temperature chart that I waved at him), fading colour filters in the enlarger head, the constant-voltage transformer that supplied the lamp, then the area-calculation device in the replenisher-dispensing system. I proved my point when I got one of the lab staff to rewind a roll so that the last to be exposed was the last to be processed. The two ends of the roll yielded identical prints.
Eventually Agfa explained that they had been using a Cadmium salt to hang onto halide ions released at exposure, but due to Cadmium's toxicity had to omit it from production. All the sensitised goods manufacturers were faced with the same problem and solved it by various means.
If you want to evaluate latent image regression in a paper emulsion, get a densitometer, expose identical, numbered patches at five-minute intervals, process the last as soon as possible after exposure and plot the reflection densities against time. You may measure a difference between the last two but not much thereafter.
Try the same test with films, but don't rely on the shutter or the auto-diaphragm - set the aperture manually and use neutral-density filters and the lens hood to control the exposure. Start with Ilford Pan-F Plus and then progress to Delta 3200 (whose packaging carries the advice to process soon after exposure). Then publish your results! You'll be judged a hero!
Film manufacturers know best. They hire graduate scientists, who carefully devise experiments and carry them out meticulously with research-grade equipment .
By the way, your freezer will help. Captain Scott's photographer Herbert Ponting took some amazing photographs during the ill-fated expedition to the South Pole, as did Scott himself. Some were processed months after exposure - others decades later.

None of this has anything to do with pictorial photography.
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Old 7th September 2020, 05:58 PM
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skellum skellum is offline
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I wonder if we'll ever put this to bed?
Unlike Richard I've never seen such rapid image degradation on PanF.
I've had rolls of film in the camera for weeks at a time, and when processed frames 1 and 12, exposed some time apart, looked just the same. A couple of years ago I processed some 20+ year old PanF which retained a very faint and unprintable ghost image on the film.
There are a few possible variables- freshness of the film when loaded, and storage after expsure for example.

I think we all process our film as promptly as we can- I can't imagine anyone here choosing to delay development.
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Old 7th September 2020, 06:34 PM
Mike O'Pray Mike O'Pray is offline
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Jo so slow films like Pan F+ should exhibit the least latent image fade compared to D3200 and certainly there should be a noticeable difference even between HP5+ and Pan F+?

How long post exposure would Terry need before he would notice the difference between the two films?

There has been a recent thread on Photrio where a member asked about the latent image fade of HP5+ and the consensus seemed to be that HP5+ had no latent image problems to speak of and that this lay with Pan F+ which as I said even Simon Galley admitted to

In your test between say Pan F + and D3200 did your research/experience indicate how much worse a fast film like D3200 was compared to Pan F+

I take it there is no formula that helps illustrate this or is there?

Thanks

pentaxuser
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Old 8th September 2020, 03:06 PM
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photomi7ch photomi7ch is offline
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The link below shows what happens to a print that has not been fixed the results surprised me.

Fading face
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Mitch

http://photomi7ch.blogspot.com/

If you eliminate the impossible whatever remains no matter how improbable must be the truth.
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Old 8th September 2020, 05:03 PM
Lostlabours Lostlabours is offline
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Quote:
Originally Posted by skellum View Post
I wonder if we'll ever put this to bed?
Unlike Richard I've never seen such rapid image degradation on PanF.
I've had rolls of film in the camera for weeks at a time, and when processed frames 1 and 12, exposed some time apart, looked just the same. A couple of years ago I processed some 20+ year old PanF which retained a very faint and unprintable ghost image on the film.
There are a few possible variables- freshness of the film when loaded, and storage after expsure for example.

I think we all process our film as promptly as we can- I can't imagine anyone here choosing to delay development.
Pan F is the only film I've had an issue with, and it was my own fault. I put a roll through my Micrord, and then used half a second, I intended to finish the film off and process both together, a year later I realised I hadn't. Both film were toast but then there weren't any images I'd any plans for.

Agfa AP25 then later APX25 had a chemical in its emulsion that helped tame the contrast as well as the latent image issue, when this chemical became unavailable it was too expensive to re-formulate the emulsion as sales were so low.

Current Pan F Plus datasheets suggest developing within a reasonable time, there's nothing like that in a 1982 Pan F datasheet.

Ilfod
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Old 8th September 2020, 06:14 PM
Mike O'Pray Mike O'Pray is offline
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I had a look today at the Ilford specs on D3200, HP5+ and Pan F+

On D3200 I found a reference to its greater susceptibility to airport scanner damage and on both this film and HP5+ Ilford advises process as soon as possible but is not more specific than this that I can find. While I haven't checked other Ilford film specs, I suspect that "process as soon as possible" is a catch-all added to all its films

The exception to this is Pan F+ where it mentions specifically latent image fade and to my surprise it mentions a time of within 3 months

So I take back some of my assertions that Ilford were numb and vague about a specific period within which to process for Pan F+

Certainly 3 months is quite a long period as a safety margin. So not a matter of a few weeks at least

Mike
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Old 8th September 2020, 06:55 PM
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skellum skellum is offline
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Hi Ian-
Agfapan 25 was a really beaufiful film. I had always been a PanF user, and only chanced on the Agfa film when I couldn't find any PanF. It was so good I was tempted to switch, only for Agfa to discontinue it! It was easier to print than PanF, and had a gorgeous tonality.
Happily I now have a 'recipe' for PanF which manages the contrast without drama.
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