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

[Diana Bloomfield]

Francesco,

I've only used very long exposures with pinhole cameras as well.  Of  
course, there are published reciprocity charts out there.  (Check Eric  
Renner's 'Pinhole Photography: Rediscovering a Historic Technique').   
Although his published charts include only pinhole F-stops, I still  
think you could glean something from them.  And I do think that the  
information that comes with film (or used to?) is fairly accurate-- at  
least for me.

But from my experience, I agree with Gord here that some films "don't  
seem to vary significantly past a certain duration of exposure."   
That's certainly been my experience (and not just with this high  
contrast film).

I will also add that the published reciprocity charts I used never  
seemed to offer all that much help to me.  I typically base my long  
exposures on the type of film, the type of (pinhole) camera I'm using,  
and the available light-- basically calculated guesswork, erring on  
the side of over-exposure.  (Quite scientific!).  But with the right  
development,  I never seemed to have a problem.

Diana

On Jan 19, 2012, at 11:53 PM, Gordon J. Holtslander wrote:

> 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