Pulled film and reciprocity failure calculations

[CharlesDAMorgan]

I ask this question gingerly, mostly through fear of being shown to be horribly wrong, but here goes.

Many of the developers I use give better results with films pulled to a lower EI - so Erik's excellent Tmax400 at 200 in Perceptol 1:2 or many of the PMK Pyro developed films that Chris Crawford gets superlative results from at lower EIs.

When using pinhole or large format I regularly get into reciprocity failure territory (actually I want long exposures with the pinhole - it reduces the risk of my thumb appearing in the exposure operating the shutter). Manufacturers publish reciprocity failure calculations to adjust for this - but to the best of my knowledge and belief all are at box speed.

How would you calculate exposure time where the film has been pulled?

 

[BernardL]

Manufacturers publish reciprocity failure calculations to adjust for this - but to the best of my knowledge and belief all are at box speed.

Exposure times with reciprocity failure are extended times, taking in effect the decreased sensitivity (at the toe) at low illuminations; you may consider them to be at a pulled EI. Probably the very notion of EI loses meaning once you are into reciprocity failure domain.

Bottom line: expose with RLF correction, and develop for pulled development. The reduced development time is not so much motivated by the toe exposure as by the increased contrast caused by RLF. After one or two experiments, you will have the correct numbers for your camera, your film, and your development method.

 

[Chriscrawfordphoto]

I ask this question gingerly, mostly through fear of being shown to be horribly wrong, but here goes.

Many of the developers I use give better results with films pulled to a lower EI - so Erik's excellent Tmax400 at 200 in Perceptol 1:2 or many of the PMK Pyro developed films that Chris Crawford gets superlative results from at lower EIs.

When using pinhole or large format I regularly get into reciprocity failure territory (actually I want long exposures with the pinhole - it reduces the risk of my thumb appearing in the exposure operating the shutter). Manufacturers publish reciprocity failure calculations to adjust for this - but to the best of my knowledge and belief all are at box speed.

How would you calculate exposure time where the film has been pulled?

Pulling or pushing doesn't affect reciprocity failure. you meter at whatever EI you're shooting the film at, then add whatever compensation is needed for the shutter speed you're using.

 

[CharlesDAMorgan]

Simple, clear concise Chris - thanks.