Reciprocity correction for B&W films

[Terrence Brennan]

I am looking for a table of approximate reciprocity correction for B&W films. The one I have is from an old and very tattered Kodak publication, and has a nifty graph to go along with it.

I cannot find it at Kodak's web site, or on the web, although there are many references to general reciprocity correction information. Do any APUGers know where I might find this table/info?

 

[Anon Ymous]

You can find data for reciprocity correction for each film, although charts are probably generic.

 

[Lee L]

(there was a url link here which no longer exists)
is the most thorough discussion here on APUG.

A more recent one is here, with some fits to a Foma film.
(there was a url link here which no longer exists)

There is no single answer. The generic curves/corrections from Kodak are decades old, and typically call for more correction than necessary with more modern emulsions. The first thread mentioned has some information on 5 films that were tested carefully by Howard Bond.

There are several ways to calculate corrections, all can be within a fraction of a stop of each other.

Lee

 

[Bruce Watson]

I am looking for a table of approximate reciprocity correction for B&W films. The one I have is from an old and very tattered Kodak publication, and has a nifty graph to go along with it.

I cannot find it at Kodak's web site, or on the web, although there are many references to general reciprocity correction information. Do any APUGers know where I might find this table/info?

The problem I have with these tables is that they imply that the entire film goes into reciprocity failure at once. Generally this is not the case. In general, only the shadow areas of the image are in reciprocity failure while the rest of the image is fine. In the shadows the film isn't seeing enough photons to create a latent image -- it's more of a threshold failure.

What the tables teach you is to increase exposure. You have to do this so that the shadows see enough photons to cross the threshold and create a latent image. Of course areas of the film that are not in reciprocity failure get the same increase in exposure and are therefore over exposed. Thus the recommendation to decrease development time -- to try to keep the highlights from getting too dense.

The reality is that reciprocity tables are an attempt to offer a one-size-fits-all solution to a problem with a huge range of "sizes" if you will. With roll film this may perhaps be a reasonable compromise, IDK. With sheet film the answer is to think about what you are doing and treat each film individually.

Also, I suspect that for each individual film stock, processing for reciprocity failure may depend on workflow -- particularly on developer choice and agitation style. But I've never made the effort myself to chart this, nor have I found any such research by others.

I'm just sayin' that the tables are a very rough place to start and that you'll likely have to do a fair amount of tuning to get results you are pleased with.

 

[Lee L]

The problem I have with these tables is that they imply that the entire film goes into reciprocity failure at once. Generally this is not the case. In general, only the shadow areas of the image are in reciprocity failure while the rest of the image is fine. In the shadows the film isn't seeing enough photons to create a latent image -- it's more of a threshold failure.

This is more true of older formulations that of new ones. See:
http://www.phototechmag.com/articles/articles/200705/0403Bond_Reciprocity2.pdf

He found that several of the newer formulations he tested in 2003 didn't have increased contrast, i.e. they have equal (or nearly equal enough) reciprocity failure across the typical tonal scale, from shadows through highlights.

Lee

 

[JOSarff]

Here's a table I found. You may need to adjust.

 

[Bruce Watson]

This is more true of older formulations that of new ones. See:
http://www.phototechmag.com/articles/articles/200705/0403Bond_Reciprocity2.pdf

He found that several of the newer formulations he tested in 2003 didn't have increased contrast, i.e. they have equal (or nearly equal enough) reciprocity failure across the typical tonal scale, from shadows through highlights.

Lee

It's true that more modern films have more linear characteristics in departure from reciprocity. So what Bond says makes some level of sense if the whole scene is experiencing a departure from reciprocity. Then the increased exposure wouldn't much matter to the higher values.

But if the highlight values are *not* experiencing a departure from reciprocity, then increased exposure (needed to hold shadow detail) will give you increased highlight density. Has to if reciprocity holds, which it does in this case.

I seldom shoot at night or even much at dusk or dawn anymore. But with 5x4 I often see exposures that are in the one second range. When I was shooting Tri-X I would either get loss of shadow detail or too much highlight density (I found it difficult to control at any rate). When I switched to 400Tmax this problem largely just vanished. From a practical point of view 400Tmax has considerably better reciprocity failure characteristics which means that I don't bother to compensate any more unless the indicated exposure is longer than about 4 seconds. Even then the film's response is much more linear.

 

[Lee L]

Here's a table I found. You may need to adjust.

Much of the data on that graph is from generic curves that no longer apply. Note that the (non-ortho) Ilford films all have the same corrections. That bears no relation to any of the test data I've seen over the last decade from people like Howard Bond and astrophotographers who systematically test films. Nice table, but a lot of it is garbage in, garbage out, the 'garbage in' being about 3 decade old general recommendations. If you can find specific data from a single film's technical information sheet that is a departure from the old "standard recommendation", then you might be looking at something you can work with. Otherwise you can safely assume that it could be pretty far off.

See if you can find a book on astrophotography written after 1995 or so. Michael Covington and Robert Reeves are good places to start, and they'll have much more realistic recommendations for specific films based on tests of more recent films.

Lee