Colour film - long exposures

[davidgc]

Has anybody tried long exposures using colour negative film, in particular, Kodak Portra 160?
The data sheet says undertake tests for anything longer than i (1?) second.

Can neutral density filters be used in the same way ? I don't see why not, but I understand in digital they can leave a colour cast.

Thanks, David

[Argentum]

the film data sheet should say the normal usage exposure times.

Anything more than 1 sec required will put into reciprocity. How much is dependant on the particular film and will lead to strange colours. Check the datasheet for reciprocity corrections. They may recommend filters to use when using long exposures to correct colours.

edit:

Just looked and datasheet doesn't give you any advice except as you say: test for yourself.

[davidgc]

You would think a company like Kodak would have undertaken some testing to come up with ball park figures or is colour film fairly variable in consistency compared to black and white film?

David

[John King]

I would think that reciprocity failure would be the least of you difficulties!

With long exposures, say several seconds, you will start to get 'crossed curves' where one of the colour layers will expose more or less than another. The resulting image will probably have colour casts all over the place. The longer the exposure, the more pronounced the effect will be

Just think of a colour negative which has been exposed in a room with mixed lighting, tungsten, natural daylight and phosphorescent tubes, as an analogy that is the sort of result you will probably achieve.

Using something like Photoshop you will probably be able to get around it but with conventional printing you are on a hiding for nothing

[davidgc]

Thanks John. That goes some way to explaining why there is no reciprocity values provided in the data sheet, probably for that very reason.

David

[photomi7ch]

I have used colour film with my pinhole camera. It was Fujicolour and it was out of date. There was not any colour shift that I could see with this film, that is not to say that it may happen but not in this case. I used the same reciprocity factor that I normally use with black and white as follows 1- 5 sec x2, 5-50 sec x25, 50 sec plus x12.

[davidgc]

I was going to follow the reciprocity values for Ilford as a starting point and then the values provided by a fellow member determined by Les McLean. But then your formulas seem easier to remember so will given them a try as well.

Thanks, David

[JOReynolds]

Once upon a time there were two film types of Vericolor Professional film, S and L. Type S was balanced for short daylight exposures and electronic flash. Type L was balanced for tungsten - 3200K as I recollect - and long exposures. These were negative (C41) films - there were corresponding Ektachromes (E6). Eastman Kodak published a reciprocity-failure compensation table for Vericolor II type L film, packed with 120 and sheetfilm. They also made recommendations on camera filtration and exposure for long exposures in daylight using Vericolor type S (which was balanced for realistic skin-tones with flash).
I found mention of Fuji 64T Type II, a negative film balanced for 3200K, on the internet and looked up Fuji's published data, which claims 'improved reciprocity characteristics. Enables long exposures to be made under lowlight conditions or when using small diaphragm openings for increased depth-of-field. Under these shooting conditions, any decreases in film speed and changes in color balance are minimal'
These are significant claims. Fuji also publish recommended filtration when using this film for long exposures in daylight.

[davidgc]

Thanks for this.
Up to 64 secs no compensation is required and then only a 1/3 stop and 1/2 stop for 128 and 256 secs.
It does not seem very much, from my inexperienced point of view, but then it is a lot more light when taken over several minutes; I only have Ilford times to compare against.

David

[JOReynolds]

I just looked up some notes I made thirty years ago on image regression - the fading of images between exposure and processing - after discussions with technicians from Kodak, Fuji and Agfa. They were all a bit cagey because there are/were lots of trade secrets in emulsion technology, so this info is incomplete.
Emulsion chemists used to put a pinch of something toxic into their potions to prevent regression. Environmental scientists in Germany traced this stuff (I think it may have been Cadmium) back to photoprocessing labs and pressed film and paper manufacturers to remove it from their products (their Green Party was holding sway). Agfa removed it immediately and the effect was obvious - differences between the beginning and end of a roll of identical publicity prints, because the beginning was the last to be exposed and the end might have been exposed the night before. I was selling processing machines at the time and it was the machine that came under suspicion, so I had to find an answer, double-quick. The client was persuaded to install a voltage stabilizer. I built a chart recorder to log temperature variations and did Ceric oxide titrations every few days to gauge developer activity. The client changed the brand of machine, at a cost of more than ten thousand pounds, but it didn't solve the problem. Eventually the in-house carpenter build a re-reeling rig so that the first to be exposed was now the first to be processed. That worked.
Kodak and Fuji solved the problem of image regression without a fuss - perhaps they were not relying on Cadmium?
Incidentally, the temperature chart recorder is up for grabs - anyone want it? 2cm = 1deg C. Paper rolls difficult to come by.

[KevinAllan]

I have used Portra 160 for studio still life's with exposures of up to 16 seconds and have allowed 1 stop for reciprocity failure and they worked fine. Bear in mind that Portra has a wide exposure latitude which helps. Try bracketing for a test roll and take it from there.