Film speed pulling and reciprocity

[brit]

How do you deal with reciporcity when pulling a film at exposure? Do

you act still on the film data and your actual meter readings, (eg

start adjusting at 0.5 sec or whatever the tech sheet says) or do you

adjust when reciprocity failure for the the nominal speed is reached.

I'll explain that last sweeping statement for you: For example Delta

400 is often rated at 100 for dev in PMK, so in this situation would

you begin to adjust exposure at 1/2 sec at 100 or at 1/125 in

realising its nominally rated (and fairly accurately too so I read)

at 400?

 

Bri

[art_haykin]

According to Ilford, reciprocity failure is not a significantfactor with Delta 400 at shutter speeds from 1/2 second to 1/10,000th. As for rating it at 100, I don't know, but you'dcertainly lose contrast.

[pete_andrews]

Reciprocity failure is caused by exposing a film to very low light levels for long exposure times, or very high levels for very short times. It's the duration of the exposure that matters, not the rated speed. So the compensation still needs to be based on the manufacturer's data; i.e. 1/2 second and longer.<br>Another way of looking at it is that the proposed development doesn't alter the film in any way. Before you develop it, the film doesn't 'know' if it's being rated at 100, 400, or 16000 ISO, and the halide crystals will react to exposure time and intensity in exactly the same way, regardless.

[roger_michel]

i rate my tri-x sheet film at 200, but always use the regular reciprocity figures provided by kodak. i think the above poster must be correct.