Portra 400 long exposures
Sorry if this was talked before.
I will probably need to long expose some Kodak Portra 400 (new one). In it's manual, no adjustment is mentioned < 1 second, and after they say we should "test". I can't make so many tests, take into consideration it will be the first time I will develop C-41 (at home, no processor, only good thermometer and will).
How should I adjust exposure ? (I will shoot maximum 1 minute)
If it were me, I would use the recommendations given for their T-Max films as a starting point.
Try a search. I read a thread recently about it. I don't think a chart has been published though.
Aren't the charts for tmx and tmy completely different?
I'd read that anything more than a couple seconds, doubling the exposure was a good start, triple for really long. Haven't tried it yet as iso 400 was a bit too fast on a sunny day in my pinhole.
This might be of some help:
Also, this film can handle a good deal of overexposure, so I'd err on that side of things.
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There's Figital Revolution, suggesting doubling or tripling exposure times:
Don't guestimate and just increase your exposure willy nilly.
I did that with Konica Centuria and paid the price for it with shitty images.. turns out it has no reciprocity effect until after 10 seconds... even the 1600 & 3200 stuff did too.
One roll test, bracket, bracket, bracket. Most films are decent to 1 second so shoot from widest aperture at 1s to narrowest aperture with the equivalent exposure values (e.g. 1s f/4, 2s f/5.6, 4s f/8, 8s f/11, 16s f/16, 32s f/32, 64s f/64) in the same light. Develop and check the density to see what the reciprocity characteristics are like. If 32s is half as dense and 64s is one quarter as dense you know what you need to do. A test like this is the only way to know for sure.
If you can't do a test roll first then bracket apertures at 60s instead. Shoot f/4 at 60s to f/11 at 60s to be sure you get something. Heck, shoot f/2.8 to f/32 if you have time.
Sorry for the answer, but if the work is important I would go for some material which can better stand long exposures. Maybe you like the palette of Portra better, but if you have to "test" long shutter times it means you are not going to get the colours right easily.
Just as an example, I went and look the technical sheet of Fujifilm Superia Xtra 400:
No exposure or color balance compensation is required
for exposures within a 1/4000 to 2 second shutter speed
range. However, for exposures of 4 seconds or longer,
provide the compensations indicated below.
[They say: 4 seconds: add 1/3EV; 16 seconds: add 2/3 EV; 64 seconds: add 1 EV]
Except for special effects, the normal intensity ratio for
main-to-fill subject lighting should remain within 1:4 limits
In no way I am stating that this film is better or worse than Portra 400. It just seems to me that it might be much less hassle for the job you are planning. Fuji states no compensation filters, as I understand it, up to 64" exposure.
Portra should end up faster.