Reciprocity failure times

[Paul Corcoran]

Greetings all,

just wondering if anyone had advice on additional exposure times for kodak portra 160NC. I was shooting earlier and as it was quiet dark and i was using a high dof (f22) the meter reading was 1 minute should i add some extra time for an exposure this long?

anybody got a set of guidelines they find work for them so i don't have to go waisting a load of expensive film? it would be much appreciated

Thanks again

[Bob Kerner]

Paul, I think this has been asked here before so you might try a search. I've looked for the same info myself.

Here's what the tech paper says: "Adjustments for Long and Short Exposures
No filter correction or exposure compensation is required for PORTRA 160NC, 160VC, 400NC, 400VC, or 800 Films for exposures from 1⁄10,000 second to 1 second. For critical applications with longer exposure times, make tests under your conditions."

The pdf is here http://www.kodak.com/global/en/profe...4040/e4040.pdf

I think in another thread the consensus was trial and error after one second.

[Paul Corcoran]

Thanks Bob,

I'd seen those pdfs from kodak but they really are of no use, i'm looking for additional time for exposures of 1min and above. i understand the trial and error aspect but film it a little too expensive here to have this luxury.
I had a quick search of the forum but didn't see what i was looking for but on your advice i'll cjeck again, i imagine its a very common problem so hopefully i'll find something

cheers

[Liam:]

I am also interested in this, I spent a while searching this forum and the internet but didn't find much on the subject. This is what I am now going to try using:

4 sec = +0.5 stop
15 sec = +1 stop
30 sec = +1.5 stop
1 min = + 2 stops
2 min = NR

I have not tested these times yet!

[Bruce Watson]

I am also interested in this, I spent a while searching this forum and the internet but didn't find much on the subject. This is what I am now going to try using:

4 sec = +0.5 stop
15 sec = +1 stop
30 sec = +1.5 stop
1 min = + 2 stops
2 min = NR

I have not tested these times yet!

I've used 5x4 160PortraVC out to 15 seconds with no additional time or filtering. Made a beautiful big 143 x 90 cm print from one that's hanging on a dining room wall. Excellent shadow detail, shot at EI 160.

This is what Kodak means when they say to test it yourself. Because YMMV.

[eddie]

I used the Pinhole designer for help with reciprocity. Pretty cool really. It has various films listed and calculates it all. For 1 sec I would and just a bit. Maybe 1.5 sec or 2.

[Noah A]

The Portra films have a ton of overexposure latitude, so if you can't afford extensive testing (and I understand this, believe me!), it's better to err on the side of overexposure.

The films have decent underexposure latitude too, so it's really hard to go wrong.

My exposures obviously depend on what is in the scene. If there are a lot of light sources I may go towards the bottom end of my estimates. If it's, say, a beach scene at night I may go towards the long end or longer, since there will be no real highlights to worry about. The neg films are really good at holding highlight detail though.

Up to 1 sec (metered) I shoot as metered.
5 sec (metered)=10-20 sec
10 sec (metered)=30 sec-1 minute
30 sec or more (metered, though metering gets tricky at such low levels)=5 min or more

[Paul Corcoran]

Thanks for all the replies, i have also been in touch with a photographer i meet last summer that uses long exposures in all of his work and once i get a reply from him i'll post here so that, combined with the guidelines already posted here, we might be able to establish a set of workable guidelines.

[domaz]

Color films are going to have problems with reciprocity varying in different color layers. So your colors could get really weird when you do really long exposures.

[al olson]

As a rule of thumb that I devised 6 or 8 years ago, when I am doing twilight photography, I normally start photographing approximately 40 minutes past sunset. Working with Portra 160 films I set the aperture between f/8 and f/11. The first exposure is 2 minutes, the second is at 4 minutes, and the last is at 10 minutes which coincided roughly with the end of Nautical Twilight.

The purpose of waiting to began exposing film until 40 minutes after sunset is to get richer color in the sky. The doubling of the second exposure is to give it one more EV. And the 10 minute exposure is to double it one more time and to accommodate the fading light.

As I recall, I arrived at the 2 minute exposure by making an incident light reading and comparing it with a spot reading of the sky. I believe that the metered exposure was around 30 seconds. I quadrupled the exposure to account for reciprocity failure.

I wrote a brief guide (http://www.photo-artiste.com/existinglightguide.html) that needs to be updated, but it does have some examples that you may find helpful. If you scroll down the the section, Balancing Ambient Light with Twilight, there is an example showing the three different exposures, for Kodak Ultracolor 160 film which was not very different from Portra 160. As Noah says, you can hardly go wrong with overexposure.

I am not sure where I found the following rule, perhaps in one of the older Kodak film guides: A rule-of-thumb used by many photographers is to increase the aperture by ½ to one EV if the exposure exceeds one second, by one to two EV if it exceeds 10 seconds, and increase the exposure by 2 to 3 EVs if the exposure is over 100 seconds. It is important to check the detailed information on exposure correction for long exposures that can be found in the film’s data sheet. In fact, exposure time can usually be extended for hours under the darkest night conditions without causing undue overexposure.