Reciprocity Law Failure

[Stanley Kubrick]

Could somebody explain this to me? I understand what it is, increasing exposure times as film does not react to light in the way it was intended to at longer exposures. I looked at Ilford's chart for calculating this, but I dont understand it. Is it just a case of doubling the stop by what it would normally be? I am planning on shooting 5x4 film at quite a slow speed, so I might have to do longer exposures to what I normally do, depending on the circumstance.

Thank You

[vinny]

https://www.google.com/search?q=reciprocity+failure&ie=UTF-8&oe=UTF-8&hl=en&client=safari
Read first search result under chemical photography. It's explained very clearly.

[Bill Burk]

The exposure required to reach the same result on film is a bowl or bow-shaped curve, where the bottom of the bowl is somewhat flat in the time range the film is designed for... For example between 1/1000 second to 1 second.

As the curve bows up, the necessary exposure goes up logarithmically, so it's not necessarily doubling. Each film has its own reciprocity characteristics, so when you find a chart for your film, it may not apply to other film. (So you may need to draw up a different chart for different films)...

[Ken Lee]

You might find it helpful to search the forum for earlier discussions of this topic.

Here's a graph (http://www.largeformatphotography.info/forum/showthread.php?27798-Reciprocity-calculation-for-Tmax-400&p=263829&viewfull=1#post263829) which shows that up-swept curve, provided by another forum member.

[Ken Lee]

Lately I've been experimenting with dimly lit subjects and generous bellows extension: the exposures get very long, like a minute or more.

I have found this iPhone app very helpful, because it takes everything into consideration: Reciprocity Timer (https://itunes.apple.com/us/app/reciprocity-timer/id459691262?mt=8). It paid for itself with the first few sheets of film it saved.

[rich815]

As others aptly point out you do extend exposure time above and beyond what you would following a standard linear exposure chart however if you consider using Fuji Acros film no adjustment is required for exposures up to 120 seconds, and only +1/2 stop additional for exposures between 120 and 1000 seconds. It's a wonderful film.

[Jerry Bodine]

When I started using Ilford film I noticed that the same exact curve for reciprocity was published for several of their films, so I queried them about that at the time. They responded by saying that they are a small company (compared to Kodak?) and could only provide a rough approximation rather than performing lengthy tests on each film, and a serious worker should perform personal tests on the film of choice. I found in AA's "Negative" book that he referenced Kodak's recommendations, which indicated the need to reduce dev times as the length of exposure grew in order to offset the resulting gain in contrast; AA explained the cause of the contrast increase. I've yet to see any author mention if choice of developer/dilution is a factor. Considering the variables involved, I've concluded that the serious worker who frequently works under reciprocity conditions is better off to go with Acros and keep the testing $ in his pocket to buy more film.

[photobymike]

Lately I've been experimenting with dimly lit subjects and generous bellows extension: the exposures get very long, like a minute or more.

I have found this iPhone app very helpful, because it takes everything into consideration: Reciprocity Timer (https://itunes.apple.com/us/app/reciprocity-timer/id459691262?mt=8). It paid for itself with the first few sheets of film it saved.

Holy Crap ...my iphone is even more useful thanks Ken!!

[David Karp]

I found that for the Ilford films included, the reciprocity chart in Steve Simmons's view camera book work for me (and different than Ilford's recommendations).

[Bill Burk]

You might find it helpful to search the forum for earlier discussions of this topic.

Here's a graph (http://www.largeformatphotography.info/forum/showthread.php?27798-Reciprocity-calculation-for-Tmax-400&p=263829&viewfull=1#post263829) which shows that up-swept curve, provided by another forum member.

Thanks Ken,

A piece of paper with a curve. That's what I need, since I don't have an intelligent phone...

[Ken Lee]

That curve matches the Kodak tech pubs datasheet (http://www.kodak.com/global/en/professional/support/techPubs/f4016/f4016.pdf) for TMAX films (see page 20).

Perhaps the author figured out the exponential function which matches the numbers given by Kodak.

[Nathan Everett]

I printed and cut out the little reciprocity failure tables that the film manufacturers give in their data/specifications pdf's and laminated them, they are quite small at about 3x4" and I keep them in my light meter case for easy access. Generally they give corrected times for up to about 2 mins, after this it's trial and error or use tables developed from other people's experiments.

[Heroique]

Could somebody explain Reciprocity Law Failure to me? ...Is it just a case of doubling the stop by what it would normally be?

“What it is” is one thing – what to do about it is another.

Here’s a starter’s chart that might be helpful.

It’s for times under 2 minutes for traditional b/w films (not T-grain), until one becomes more familiar w/ personal equipment & film, darkroom processing habits (such as “N-1” or “N-2”), and preferred results. As you learn more, adjust to your taste:


• Metered 2 sec. – use 4 sec (2x)
• 4 sec – use 12 sec (3x)
• 8 sec – use 32 sec (4x)
• 15 sec – use 75 sec (5x)
• 30 sec – use 3 min (6x)
• 60 sec – use 7 min (7x)
• 120 sec – use 16 min (8x)

Over time, my personal reciprocity charts for various films depart more and more from the chart above, and from manufacturing suggestions, but not by a very significant amount.

-----
Master’s note :D:
“This is commonly known as ‘failure of the reciprocity law’,” AA says in his book, The Negative, “but I prefer the term reciprocity effect as it is not actually a ‘failure.’ ”

[Stanley Kubrick]

Thats great, thanks for all the charts and info, I have more of an idea now. Im not going to be doing anything longer than two seconds, and mostly B=W, so it shouldnt prove too much of an issue. Iv heard Ektar film (Colour) performs quite well for this also, so long as its not too long.

[Bill Burk]

... Im not going to be doing anything longer than two seconds, and mostly B+W, so it shouldnt prove too much of an issue....

That's what I thought too before I started reading this thread (couple seconds at most), but maybe I will shoot some shots at several minutes in the future...

[Andrew O'Neill]

Perhaps the author figured out the exponential function which matches the numbers given by Kodak.

Ken, if you are referring to my chart which you linked to, I actually ran the tests myself, and then read the curves and plotted them by hand. I do this for all films that I use as I find that the manufacturer's data usually calls for too much compensation.


if you consider using Fuji Acros film no adjustment is required for exposures up to 120 seconds, and only +1/2 stop additional for exposures between 120 and 1000 seconds

Seriously? I'll have to test this one. I've never used this film as it's bloody expensive up here and hard to get...I mainly work in 8x10. I'll see if I can get my hands on some 4x5.

[Light Guru]

Could somebody explain this to me? I understand what it is, increasing exposure times as film does not react to light in the way it was intended to at longer exposures. I looked at Ilford's chart for calculating this, but I dont understand it. Is it just a case of doubling the stop by what it would normally be? I am planning on shooting 5x4 film at quite a slow speed, so I might have to do longer exposures to what I normally do, depending on the circumstance.

Thank You

If you have an iPhone check out the app Reciprocity Timer it calculates the adjusted exposure for you factoring in reciprocity, filters, bellows extension etc.