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/professional/support/techPubs/e4040/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.

[Paul Corcoran]

Hi All,

So i've heard back from my friend and he uses a similar general rule as mentioned at the end of Al's post basically the general rule he works to goes as follows:

upto 30sec add 1/2 stop
30sec-1min add 1 stop
1min-1 1/2min add 1 1/2 stop
1 1/2 min - 2 min add 2 stops

and so on its basically 1/2 a stop for every thirty seconds you read of your meter.

hope this helps.

[Liam:]

Thanks for reporting back Paul.

I thought reciprocity always increased exponentially...

[Paul Corcoran]

Hi All,

Just got back some negs from my test with the above set of guidelines and thought i'd share the result. I determined the exposure was 2m 15 secs at f22 and so opened up two stops and shot at f11. I'm quite happy with the result, this is the raw scan with no adjustments so i'd say those guidelines are are good starting point for this kinda work.

All the best

Paul

http://www.flickr.com/photos/paulcorcoran/5428403226/

[peter ramm]

So how does this translate to multiflash? Recently, I ran a series of trials and needed 35 x 1000ws pops (but reduced about two stops through a polarizing filter). This gave me proper exposure on 8 x 10 HP4 with a 240mm at almost 1:1, lens polarizer, f35. In this situation, I seem to remember my film plane metering was not sensitive enough to read anything so I got an incident light guide value. Of course, that was less than 10% of what I actually needed.

Factors are close to full bellows extension on the P2 and successive flashes. I can get the bellows factor, but have not found a reciprocity treatment for multiple flashes. In this case, the bellows factor appeared to account for most of the required increase in exposure. I guess each successive flash is less efficient than the one before but how much?

Any guidance?

[Robert Hughes]

So how does this translate to multiflash?
Reciprocity failure (https://secure.wikimedia.org/wikipedia/en/wiki/Reciprocity_%28photography%29) is a consequence of long exposure. Since flash photography is instantaneous, reciprocity failure is not an issue.

Edit: guess not - as bobwysiwyg link shows below.
How short duration is an electronic flash, anyway?

[bobwysiwyg]

It's also a consequence of short exposures.

http://glenstone.sdsmt.edu/My-files/Labs/Reciprocity.pdf

[peter ramm]

As I understand it reciprocity arises because the noise floor eats a proportion of photons in dark areas - however the darkness arises. Can be from low levels of continuous lighting over time, low levels of flash illumination over pops, or short exposures.

My informal observation was that flash reciprocity was less than I expected given that the continuous exposure would have been some minutes. Just wondering if there is a common wisdom about correcting for the use of repeated flashes vs long exposures.

[Eric Bryan]

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.

Good info. I am going to give it a try with Portra 160.

[ataim]

I use this and Its never failed me. I only use Ilford HP5 and Delta

http://www.largeformatphotography.info/forum/showthread.php?80133-Reciprocity-Timer-1-0

[DavyG]

I use this and Its never failed me. I only use Ilford HP5 and Delta

http://www.largeformatphotography.info/forum/showthread.php?80133-Reciprocity-Timer-1-0

+1 ... That is a very excellent app. And it's easier to use than remembering the generic formula which I did before. It also works for colour film.