Pushing & pulling

Rate your film one stop off, then bend the dev time to match.

Bend the chemistry

Push = rate your film faster and develop longer to compensate. Pull = the opposite. Both change contrast and grain.

The numbers

+1 stop   +30% dev time, more contrast
+2 stop   +70% dev time, crunchy, grainy
-1 stop   -20% dev time, softer, flatter

Why bother

Push HP5 to 1600 and shoot a dim bar handheld. Pull when the light's harsh and you want it gentler. Same film, new personality.