[alt-photo] Re: Ultra Long Exposure Reciprocity Failure?

[Gordon J. Holtslander]

I can't offer any mathematical insights,  however the pinhole camera on 
film work I have done usually involves long exposures.

I started doing pinhole work with large format high contrast contact 
printing film and processed it with Dave Soemarko's LC1 developer mixed 
to minimize contrast in order to get a continuous tone negative.

When used with this developer the film has an effective ASA of 1.  Shots 
taken outside on a cloudy day would need an exposure of 1/2 hour.  I 
also took a series of indoor photos where the exposure time as in the 
range of 6 to 8 hours.  As long as I metered accurately my exposures 
were consistent regardless of the exposure time - from 15 minutes in 
full sun to 8 hours inside.

Used in this way the film (at the time Kodak CGP) did not seem to 
exhibit any reciprocity failure, or perhaps the reciprocity failure did 
not vary in the range of exposure I was working with.

My point is that perhaps with extremely long exposures the sensitivity 
of this film is consistent, and does not vary significantly past a 
certain duration of exposure.

It was possible to get reciprocity compensation data for certain film. 
I don't think is was calculated, but done by empirical testing of each 
type of film.

Try doing some empirical testing and see if your film shows a 
continually increase in reciprocity failure, or if it stops or decreases 
after a certain.

Photograph a grey scale in dim conditions and increase the exposure time 
and see what effect it has.

I also read that when electronic flashes were first used, some films 
suffered from reciprocity failure due to extremely short exposure times.

Hope this helps.

Gord


On 1/19/2012 8:07 PM, Francesco Fragomeni wrote:
> Hi all,
>
> I've been trying to figure something out with this for a while now and my
> guess is that the only real answer is testing but I'm hoping that someone
> here might be able to offer some mathematical insight that I haven't
> thought of or seen elsewhere. I am interested in making some ultra long
> exposures and I am looking for a way to approach calculating the rate of
> change in reciprocity failure as the exposures get longer. I understand
> that reciprocity failure is not linear but logically there should be a way
> to mathematically work out the rate of change of the failure over the
> increase in exposure. I'm probably wrong about that otherwise someone would
> probably have solved for it by now but alas I'll still put the question out
> there.
>
> A few broad questions:
>
> I understand that with Solargraphy, exposures can be made on paper (rather
> then film) for extraordinary long periods of time and reciprocity is not an
> issue partly because paper does not have the same reciprocity failure
> characteristic as film and also because in Solargraphy the latent image is
> actually burned into the emulsion in positive (I believe). For an image to
> be made in this way, must the sun actually be present in the frame and can
> these ultra long exposures be made with the sun out of the composition? I'm
> unsure of whether or not the intensity of the sun plays some role in the
> etching of the image in the paper. To me, it makes sense that these types
> of images can be made with or without the sun in the scene as they seem to
> simply be the result of gross overexposure which effectively prints out on
> the paper. Can someone confirm this or correct me if I am incorrect?
>
> In reference to ultra-long exposures on film, a good example is the work of
> Michael Wesley. I think his work was done on film. This is the basis for my
> wondering how one can make ultra long exposures into months or years using
> a material with a reciprocity failure characteristic like film has. Perhaps
> at such long exposures film behaves like paper and prints out and
> reciprocity is no longer an issue to be concerned with. Somehow I don't
> think thats the case but I suppose its a possibility. Can anyone shed light
> on this?
>
> In the end, I'm primarily concerned with learning if there is a way, an
> equation perhaps, that can be used to determine the rate of change in
> reciprocity failure over the increase in exposure time. There must be a way!
>
> Any insight from you big brains would be very helpful!
>
> Thank you!
>
> -Francesco Fragomeni
> www.francescofragomeni.com
> _______________________________________________
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>


-- 
Gordon J. Holtslander
gjh at shaw.ca